Household secondary attack rate in mild COVID-19.

Background: The coronavirus disease 2019 (COVID-19) pandemic has reached a staggering number of almost 280 million cases worldwide, with over 5.4 million deaths as of 29 December 2021. A further understanding of the factors related to the household spread of the infection might help to bring about specific protocols to curb such transmission. Objective: This study aims to find the secondary attack rate (SAR) and factors affecting SAR among the households of mild COVID-19 cases. Methods: An observational study was designed where data of patients admitted at All India Institute of Medical Sciences, New Delhi due to mild COVID-19 were collected, and outcome was noted after the discharge of the patient. Index cases who were the first in the household to have a positive infection only were included. Based on these data, the overall household SAR, factors related to the index case and contacts that affected transmissibility were noted. Results: A total of 60 index cases having contacts with 184 household members were included in the present study. The household SAR was measured to be 41.85%. At least one positive case was present in 51.67% households. Children below 18 years old had lower odds of getting a secondary infection compared to adults and elderly [odds ratio (OR) = 0.46, 95%CI = 0.22-0.94, p = 0.0383). An exposure period of more than a week was significantly associated with a higher risk of infection (p = 0.029). The rate of transmissibility drastically declined with effective quarantine measures adopted by the index case (OR = 0.13, 95%CI = 0.06-0.26, p < 0.00001). Symptomatic index cases contributed more to the SAR than asymptomatic primaries (OR = 4.74, 95%CI = 1.03-21.82, P = 0.045). Healthcare worker index cases had lower rates of spread (OR = 0.29, 95%CI = 0.15-0.58, P = 0.0003). Conclusion: The high SAR shows the household is a potential high-risk unit for transmissibility of COVID-19. Proper quarantine measures of all those exposed to the index case can mitigate such spread and lead to reduction of risk of COVID-19 within a household.

Impact of Influenza in South-East Asia

Influenza infection is asymptomatic in up to 75% of cases, but outbreaks result in significant morbidity. Reports found that severe influenza complications tend to occur among the very young (<5 years) and very old (>65 years), especially those with underlying co-morbidities like diabetes mellitus and heart disease. Even with no co-morbidity, some older persons with severe influenza may require hospitalisation or intensive care, with increased risk of myocardial infarction and stroke. In South-East Asia, influenza was often seen as a mild problem and was not deemed notifiable until the appearance of the Influenza A(H1N1) pandemic in 2009. For decades the data made available were based on extrapolated estimates collected mainly from paediatric populations, resulting in inconsistent findings. Following expanded surveillance across the region using national surveillance systems for influenza-like illness (ILI) and severe acute respiratory illness (SARI), and better diagnostic methods, improved estimates of disease burden was achieved in South-East Asia. However, two studies conducted in 2008-2010 reported findings ranging from 2-3% to 11%. With regards to increased risk of complications, the estimated global annual attack rates for influenza were 5-10% in adults and 20-30% in children, resulting in 3-5 million cases of severe illness and 290,000-650,000 deaths. A study In Singapore reported that influenza is associated with annual excess mortality rates (EMR) of 11-14.8 per 100 000 person-years, especially affecting the elderly;these rates are comparable to that of the USA. As for hospitalisation rates of children under 5 years with seasonal influenza, the USA estimated a rate of 1.4 per 100,000. Comparable rates were reported in Singapore (0.7-0.9), Thailand (2.4), Viet Nam (3.9-4.7), and the Philippines (4.7). In 2018, an updated study reported a mean annual influenza-associated respiratory EMR of 4.0-8.8 per 100 000 individuals, with South-East Asia showing a high mortality rate of 3.5-9.2 per 100,000 individuals. It was already estimated in Thailand in 2004 that influenza resulted in USD23-63 million in economic costs, with the main contribution from lost productivity due to missed workdays. Thus, comparable to countries in temperate climate, the clinical and socioeconomic impact of influenza in South-East Asia appear to be just as substantial. With the emergence of the COVID-19 pandemic in 2020, global influenza incidence dropped dramatically. In South-East Asia, the trend in influenza detections was similar to the rest of the world, with numbers slightly higher than average in early 2020, followed by a quick drop-off by the end of April 2020. After April 2020, the detection rate remained low until late July 2020, when Influenza A(H3N2) predominated in Cambodia, Malaysia, the Philippines, Singapore, Thailand and Timor-Leste;influenza B in Lao People's Democratic Republic but with an upsurge in A(H3N2) activity. Following a two-year hiatus, influenza outbreaks began to re-emerge significantly since early 2022. From February through August 2022, influenza activity in the southern hemisphere remained lower than in pre-COVID-19 pandemic years, but was at the highest level compared to similar periods since the start of the COVID-19 pandemic. Reasons for the reduction during the COVID-19 pandemic include non-pharmaceutical interventions (NPIs), reduced population mixing and reduced travel, and possibly viral interference between SARS-CoV-2 and influenza virus in the same host. In general, the reduction in influenza detections however does not appear to be associated with lack of testing. The World Health Organisation (WHO) continues to recommend that vaccination is the most effective way to prevent infection and severe outcomes caused by influenza viruses. Although influenza vaccine is not commonly used in most countries in South-East Asia, its burden is similar in other parts of the world where influenza vaccine is now routinely used. Currently, the countries in South-East Asia that are providing free influenza vacc na ion for those at high risk include Thailand, Singapore, the Philippines and Lao People's Democratic Republic.Copyright © 2023

Prevalence of Covid 19 among Returning Pilgrims at Islamabad International Airport, Pakistan, a Retrospective Cohort Study

Intro: Mass gathering events (MGEs) are associated with the transmission of COVID-19. The world's largest mass gathering hajj pilgrimage 2022 was held after two years of major disruption caused by the COVID pandemic, with one million pilgrims of different ages, health statuses, hygiene sophistication and close contact. This study aimed to estimate the Prevalence of COVID-19 among returning Pakistani pilgrims at Islamabad International Airport, its association with these MGEs and to quantify the potential risk factors associated. Method(s): A retrospective cohort study was carried out at Islamabad International Airport from 14th July to 13th August 2022. A representative sample of 1100 people with potential exposure at Hajj 2022 was surveyed by a questionnaire to obtain information about attendance at hajj and COVID-19 disease. In addition, Rapid antigen testing (RAT) against SARS-Cov-2 was implemented. Statistical analysis was done using Epi info version 7. Finding(s): A total of 1100 subjects participated in the questionnaire survey and underwent rapid antigen testing. The mean age was 49.7+/-10.4. Almost 17.9% of the respondents experienced Covid-like symptoms with sore throat and fever as the most frequent symptoms. Three cases were detected by RAT with an attack rate (AR) of 0.3%;79.7% were female. Considering MGE exposure, AR was 0.2 %. All participants were fully vaccinated with 86.5% boosted with one dose. A dose- response relationship was found between MGE attendance and the disease, (adjusted relative risk [ARR] = 3.4- 5% confidence interval [CI] 2.25-3.5). Associated risk factors with the incidence were co-morbidity (RR=5.2) and non- use of face masks (RR=9). Conclusion(s): The study highlights the significance of MGEs in COVID-19 transmission. Vaccination and booster shots significantly reduced the risk of Covid-19 transmission among the returning pilgrims. With surveillance, screening and Rapid antigen testing at Points of entry, risk of future pandemics is significantly reduced.Copyright © 2023

How Will Demographic Change Affect the Disease Burden of Future Epidemics?

Intro: The burden of infectious diseases is influenced by the structure of the population at risk. Population ageing may have implications for the disease burden of future epidemics. Moreover, changing household structures induced by population ageing may influence the dynamics of disease transmission and burden of infections transmitted via close contact interactions. We aim to investigate the impact of demographic change on the disease transmission dynamics and future disease burden and illustrate this for COVID-19 and influenza-like illness (ILI). Method(s): We simulate the Belgian population between 2020 and 2050 using an individual-based model with census data. The simulated population structures were used as input for an infectious disease model that distinguishes between exposure to infection in the household versus exposure in the community at large. We mimicked outbreaks of COVID-19 and ILI of varying total final size. Finding(s): The simulated population ages between 2020 and 2050, which also affects household size and composition. As the proportion of elderly people in the population increases, the overall attack rate slightly decreases because older age groups have fewer contacts and are therefore less likely to incur and transmit infections. Despite the lower per-person attack rate, the estimated disease burden increases as morbidity and mortality increases with the age at infection. Conclusion(s): The demographic changes induced by population ageing have an impact on the burden of future outbreaks of COVID-19 and ILI in Belgium. The shifting age distribution implies that the elderly, a population group with increased morbidity and mortality in case of infection, make up an increasing proportion of the total population. Population ageing also leads to an increasing proportion of single-person households and collective households (e.g. nursing homes) in the population. Since the household attack rate varies by household size and composition, the living arrangements of the elderly population influences the disease burden of future epidemics to some extent.Copyright © 2023

Incidence of COVID-19 Infection in Nurses and their Families: A Prospective Cohort Study in Lahore

Background: Nurses, as frontline workers, are at a higher risk of contracting COVID19 and serve as a potential source of transmitting this infection to their family members. Estimating risk in this population is critical for controlling the rate of secondary attack rate among their families.Objective: To measure the incidence of COVID-19 in nurses and their families with associated risk factors for transmission of infection.Methods: A prospective cohort study was conducted in Akhtar Saeed Medical and Dental college, Lahore and associated three hospitals. A cohort of 176 nurses was identified in March 2020 by using non-probability convenience sampling technique and was followed till September 2021. During this tenure of one and a half year, incidence was observed by following the cohort and using a self-structured questionnaire. With SPSS 23, Chi square test was applied and p value of < 0.05 was considered significant.Results: In a cohort of 176 nurses, followed for one and a half year, incidence of COVID-19 was 37(21%). Secondary attack rate among household members of these nurses was 3%. A significant association was observed between the nursing staff and exposure to their family members (p = 0.002). Vaccination rate in nurses at the start of the study was only 26%. Nurses who worked directly with COVID-19 patients reported high incidence (p = 0.009). Nurses who used Personal protective equipment (PPE) were less affected (p = 0.003). Nurses with comorbidities showed higher incidence (p =0.02). Rate of psychological distress was high (p =0.007).Conclusion: Incidence of COVID-19 among nurses was 21% with secondary attack rate of 3% in families. Protective use of N 95 mask and comorbidities were associated with incidence.

Infection-Induced Immunity Is Associated With Protection Against Severe Acute Respiratory Syndrome Coronavirus 2 Infection and Decreased Infectivity.

BACKGROUND: The impact of infection-induced immunity on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission has not been well established. Here we estimate the effects of prior infection induced immunity in adults and children on SARS-CoV-2 transmission in households. METHODS: We conducted a household cohort study from March 2020-November 2022 in Managua, Nicaragua; following a housheold SARS-CoV-2 infection, household members are closely monitored for infection. We estimate the association of time period, age, symptoms, and prior infection with secondary attack risk. RESULTS: Overall, transmission occurred in 70.2% of households, 40.9% of household contacts were infected, and the secondary attack risk ranged from 8.1% to 13.9% depending on the time period. Symptomatic infected individuals were more infectious (rate ratio [RR] 21.2, 95% confidence interval [CI]: 7.4-60.7) and participants with a prior infection were half as likely to be infected compared to naïve individuals (RR 0.52, 95% CI:.38-.70). In models stratified by age, prior infection was associated with decreased infectivity in adults and adolescents (secondary attack risk [SAR] 12.3, 95% CI: 10.3, 14.8 vs 17.5, 95% CI: 14.8, 20.7). However, although young children were less likely to transmit, neither prior infection nor symptom presentation was associated with infectivity. During the Omicron era, infection-induced immunity remained protective against infection. CONCLUSIONS: Infection-induced immunity is associated with decreased infectivity for adults and adolescents. Although young children are less infectious, prior infection and asymptomatic presentation did not reduce their infectivity as was seen in adults. As SARS-CoV-2 transitions to endemicity, children may become more important in transmission dynamics.

Active Monitoring of Persons Exposed to Patients with Confirmed COVID-19 in South of Iran

Background: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) can be transmitted through direct, indirect, or close contact with infected people by contaminated respiratory droplets or saliva. This study aimed to investigate the epidemiology of coronavirus disease 2019 (COVID-19) and the secondary attack rate (SAR) in the cases' close contact. Methods: A total of 431 confirmed COVID-19 patients were randomly selected using systematic random sampling from 15 May to 13 June 2020. The required data were extracted from the CORONALAB database of the Center for Disease Control and Prevention (CDC) at Shiraz University of Medical Sciences. Detection of COVID-19 was performed using Real-Time Polymerase Chain Reaction (RT-PCR) and nasopharyngeal swabs. SAR was also calculated for different groups. Results: Among the index cases, 64.27% were male, 24.80% were public sector employees, and 4.87% were admitted to the intensive care unit. In addition, most of them aged 30-39 years. The SAR was 11.56% (95% CI: 9.86% to 13.25%) in the close contacts. Accordingly, the highest SAR was observed among the friends, 19.05% (95% CI: 7.17% to 30.92%), followed by the spouses of COVID-19 cases, 16.67% (95% CI: 10.81% to 22.51%). Furthermore, diabetes (6.03%) and cardiovascular disease (5.1%) were the most common comorbidities among the index cases. Conclusion: The findings suggested that the SAR was relatively lower among the close contacts. Considering the familial and non-familial relationships between the index cases and their close contacts were the major causes of disease transmission. Therefore, it is crucial to conduct tracing for COVID-19 contacts in all cases with whom patients have had close contact. © 2023 Authors. All rights reserved.

Household Secondary Attack Rate of COVID-19 among Healthcare Workers and Related Factors

Background: The risk for transmission of COVID-19 to people in close contact with infected people, especially healthcare workers, has not been well estimated. Therefore the present study was conducted to assess the household secondary attack rate (SAR) of COVID-19 among healthcare workers and related factors. Material(s) and Method(s): The present prospective case-ascertained study was conducted on 202 healthcare workers with confirmed COVID-19 in Hamadan, diagnosed from March 1, 2020, to August 20, 2020. For households with close contact with the index case, RT-PCR was performed regardless of symptoms. We defined SAR as the proportion of secondary cases from the total contacts that live in the index case household. SAR was reported as a percentage and 95% confidence interval (CI). Multiple logistic regression was performed to explore the predictors of COVID-19 transmission of index cases to their households. Result(s): We found 36 secondary cases out of 391 household contacts with laboratory confirmation (RT-PCR), representing a household SAR of 9.2% (95% CI: 6.3, 12.1). Among factors related to the family member, female gender (OR: 2.9, 95% CI: 1.2, 6.9), being the patient's spouse (OR: 2.2, 95% CI: 1.0, 4.6), and living in the apartment (OR: 2.78, 95% CI: 1.24, 6.23), and among factors related to index cases, hospitalization (OR: 5.9, 95% CI: 1.3, 26.9) and caught (OR: 2.4, 95% CI: 1.1, 5.2) were the significant predictors of disease transmission to other family members (P<0.05). Conclusion(s): The findings of this study suggest that the SAR is remarkable in household contacts of infected healthcare workers. Some characteristics of family members of the index case, including female gender, being the patient's spouse, and living in the apartment, and some characteristics of the index case, including hospitalization and caught, were associated with the increased SAR.Copyright © 2022 NRITLD, National Research Institute of Tuberculosis and Lung Disease, Iran.

Risk Factors Associated with the Spatiotemporal Spread of the SARS-CoV-2 Omicron BA.2 Variant - Shanghai Municipality, China, 2022.

What is already known about this topic?: Previous studies have explored the spatial transmission patterns of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and have assessed the associated risk factors. However, none of these studies have quantitatively described the spatiotemporal transmission patterns and risk factors for Omicron BA.2 at the micro (within-city) scale. What is added by this report?: This study highlights the heterogeneous spread of the 2022 Omicron BA.2 epidemic in Shanghai, and identifies associations between different metrics of spatial spread at the subdistrict level and demographic and socioeconomic characteristics of the population, human mobility patterns, and adopted interventions. What are the implications for public health practice?: Disentangling different risk factors might contribute to a deeper understanding of the transmission dynamics and ecology of coronavirus disease 2019 and an effective design of monitoring and management strategies.

Household transmission dynamics of COVID-19 among residents of Delhi, India: a prospective case-ascertained study.

Objective: The aim of this study was to observe the secondary infection rate and transmission dynamics of COVID-19 among household contacts, and their associations with various factors across four dimensions of interaction. Methods: This was a case-ascertained study among unvaccinated household contacts of a laboratory-confirmed COVID-19 case in New Delhi between December 2020 and July 2021. For this study, 99 index cases and their 316 household contacts were interviewed and sampled (blood and oro-nasal swab) on days 1, 7, 14, and 28. Results: The secondary infection rate among unvaccinated household contacts was 44.6% (95% confidence interval (CI) 39.1-50.1). The predictors of secondary infection among individual contact levels were: being female (odds ratio (OR) 2.13), increasing age (OR 1.01), symptoms at baseline (OR 3.39), and symptoms during follow-up (OR 3.18). Among index cases, age of the primary case (OR 1.03) and symptoms during follow-up (OR 6.29) were significantly associated with secondary infection. Among household-level and contact patterns, having more rooms (OR 4.44) and taking care of the index case (OR 2.02) were significantly associated with secondary infection. Conclusion: A high secondary infection rate highlights the need to adopt strict measures and advocate COVID-19-appropriate behaviors. A targeted approach for higher-risk household contacts would efficiently limit infections among susceptible contacts.

COVID-19 Outbreak during Summer Courses at an Elementary School.

Due to the COVID-19 emergency, face-to-face classes were suspended. After the vaccination of teachers and to mitigate educational backwardness, the schools have begun to reopen with protocols established by the government. Here, we investigated the COVID-19 outbreak in summer courses during the reopening of a private elementary school in July 2021. We report confirmed cases of COVID-19 in staff members, students, and their families. A total community of 290 people was part of this study, and we built the contact network. The clinical features of all cases are described. We used the methodology of cases and contacts. The index case was identified by epidemiological tracking, and containment measures were activated, as well as further infection chains in the setting. We estimate the attack rate for staff members at 15.68% (95% CI 7.0-28.6), students at 12.24% (95% CI 4.6-24.8), and family members at 2.6% (95% CI 0.8-6.0). An incubation period of 48-72 h was determined. A student-teacher-student-family transmission sequence was identified. The area where the infection was identified was the school swimming pool, an area where face masks are not worn or, in some cases, inadequately used. Finally, we continue with intermittent staff testing and early detection actions, reinforcing prevention measures, environmental control, cleaning, and educational interventions with students regarding the implementation of preventive measures through classes led by school health staff.

An early return-to-work program for COVID-19 close contacts in healthcare during the Omicron wave in Japan

During the coronavirus disease 2019 (COVID-19) pandemic, maintaining adequate staffing in healthcare facilities is important to provide a safe work environment for healthcare workers (HCWs). Japan's early return-to-work (RTW) program may be a rational strategy at a time when there is an increased demand for the services of HCWs. We assessed whether the early RTW program for HCWs who have been in close contact with a COVID-19 case in our hospital was justified. Close contacts were identified according to the guidance document of the World Health Organization. HCWs who met all of the following conditions were eligible to apply to an early RTW program: (1) difficult to replace with another HCW, (2) received the third dose of a COVID-19 mRNA vaccine, (3) a negative COVID-19 antigen test before each work shift, and (4) consent from relevant HCWs and their managers to participate in the program. Between January and March 2022, 256 HCWs were identified as close contacts (median age, 35 years;192 female). Thirty-seven (14%) secondary attack cases of COVID-19 were detected. Among 141 HCWs (55%) who applied to the early RTW program, nurses and physicians comprised about three-quarters of participants, with a higher participation rate by physicians (78%) than nurses (59%). Eighteen HCWs tested positive for COVID-19 by the sixth day after starting the early RTW program. No COVID-19 infection clusters were reported during the observation period. These findings suggest that the early RTW program for COVID-19 close contacts was a reasonable strategy for HCWs during the Omicron wave. © 2022 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases

Limited role of children in transmission of SARS-CoV-2 virus in households-Immunological analysis of 26 familial clusters.

BACKGROUND: The impact of children on the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains uncertain. This study provides an insight into distinct patterns of SARS-CoV-2 household transmission in case of pediatric and adult index cases as well as age-dependent susceptibility to SARS-CoV-2 infection. METHODS: Immune analysis, medical interviewing, and contact tracing of 26 families with confirmed SARS-CoV-2 infection cases have been conducted. Blood samples were analyzed serologically with the use of a SARS-CoV-2-specific IgG assay and virus neutralization test (VNT). Uni- and multivariable linear regression and mixed effect logistic regression models were used to describe potential risk factors for higher contagiousness and susceptibility to SARS-CoV-2 infection. RESULTS: SARS-CoV-2 infection could be confirmed in 67 of 124 family members. Fourteen children and 11 adults could be defined as index cases in their households. Forty of 82 exposed family members were defined as secondarily infected. The mean secondary attack rate in households was 0.48 and was significantly higher in households with adult than with pediatric index cases (0.85 vs 0.19; p < 0.0001). The age (grouped into child and adult) of index case, severity of disease, and occurrence of lower respiratory symptoms in index cases were significantly associated with secondary transmission rates in households. Children seem to be equally susceptible to acquire a SARS-CoV-2 infection as adults, but they suffer milder courses of the disease or remain asymptomatic. CONCLUSION: SARS-CoV-2 transmission from infected children to other household members occurred rarely in the first wave of the pandemic, despite close physical contact and the lack of hygienic measures.

Evaluating SARS-CoV-2 Surveillance Strategies at the United States Naval Academy: A Comparison of Saliva and Dried Blood Spot Serosurveillance Against Molecular-Confirmed Case Detection

Background. Congregate military populations remain at risk of SARS-CoV-2 outbreaks and the optimal surveillance approach in such settings remains unclear. We enrolled midshipmen at the United States Naval Academy (USNA) in a setting of frequent PCR screening use of prevention strategies. Methods. Dried blood spots (DBS) and saliva were collected in August 2020, December 2020, February 2021 (saliva only) and April/May 2021 to measure anti-SARS-CoV-2 spike (S) and nucleoprotein (NP) IgG. COVID-19 vaccine history and records of SARS-CoV-2 PCR tests and routine asymptomatic screening assays were obtained from the USNA Brigade Medical Clinic. Attack rates were compared with cumulative frequencies of infections. Concordance of saliva and DBS anti-NP and anti-S IgG positivity was determined using Cohen's kappa coefficient. Results. The study enrolled 181 midshipmen. COVID-19 vaccinations were administered in March/April 2021. Samples were collected for 101 participants in August, 73 in December, 57 in February (saliva only), and 63 in April/May. In August, 17 (17%) participants showed evidence of SARS-CoV-2 infection based on anti-S IgG values from DBS and/or saliva. By December 2020, anti-S seroconversion was observed for 5 more based on DBS and/or saliva. By May 2021, 100% of participants were anti-S IgG seropositive after vaccination based on DBS and/or saliva;48% of participants had seroconverted to anti-NP IgG. Among participants with both DBS and saliva samples, a coefficient of 0.64 showed substantial agreement between anti-S IgG results in August and perfect agreement in December (Table 1). DBS and saliva results for anti-NP IgG were in perfect agreement through December and in substantial agreement in May (0.68, Table 2). Prior to vaccination in March/April 2021, 4/48 of participants had at least one documented SARS-CoV-2 PCR positive result (Table 3). Cumulative PCR test positivity concordance with DBS seroconversion was 37.5% and 60% for anti-S IgG and anti-NP IgG, respectively. Conclusion. There was a substantive SARS-CoV-2 attack rate before vaccination;all vaccinees mounted an anti-S IgG response in blood. We note high agreement between DBS and saliva for IgG measurement. Serology-based surveillance identified substantially more SARS-CoV-2 infections than PCR screening.

Association Between Population-Level Factors and Household Secondary Attack Rate of SARS-CoV-2: A Systematic Review and Meta-analysis.

Background: Accurate estimation of household secondary attack rate (SAR) is crucial to understand the transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The impact of population-level factors, such as transmission intensity in the community, on SAR estimates is rarely explored. Methods: In this study, we included articles with original data to compute the household SAR. To determine the impact of transmission intensity in the community on household SAR estimates, we explored the association between SAR estimates and the incidence rate of cases by country during the study period. Results: We identified 163 studies to extract data on SARs from 326 031 cases and 2 009 859 household contacts. The correlation between the incidence rate of cases during the study period and SAR estimates was 0.37 (95% CI, 0.24-0.49). We found that doubling the incidence rate of cases during the study period was associated with a 1.2% (95% CI, 0.5%-1.8%) higher household SAR. Conclusions: Our findings suggest that the incidence rate of cases during the study period is associated with higher SAR. Ignoring this factor may overestimate SARs, especially for regions with high incidences, which further impacts control policies and epidemiological characterization of emerging variants.

Lower transmissibility of SARS-CoV-2 among asymptomatic cases: evidence from contact tracing data in Oslo, Norway.

BACKGROUND: Asymptomatic COVID-19 cases have complicated the surveillance and tracking of the pandemic. Previous studies have estimated that 15-25% of all infectees remain asymptomatic. METHODS: Based on contact tracing data from Oslo, Norway, we estimated transmission and susceptibility dynamics among symptomatic and asymptomatic cases and their contacts as identified by manual contact tracing between September 1, 2020, and September 1, 2021. RESULTS: Among 27,473 indexes and 164,153 registered contacts, the secondary attack rate (SAR-14) was estimated to be 28% lower through asymptomatic exposure (13%) compared to symptomatic exposure (18%). Furthermore, those infected by asymptomatic cases were almost three times more likely to be asymptomatic compared to those infected by symptomatic cases. CONCLUSIONS: Symptomatic cases spread the virus to a greater extent than asymptomatic, and infectees are more likely to be asymptomatic if their assumed infector was asymptomatic.

Reasons for SARS-CoV-2 infection in children and their role in the transmission of infection according to age: a case-control study.

BACKGROUND: The locations where children get exposed to SARS-CoV-2 infection and their contribution in spreading the infection are still not fully understood. Aim of the article is to verify the most frequent reasons for SARS-CoV-2 infection in children and their role in the secondary transmission of the infection. METHODS: A case-control study was performed in all SARS-CoV-2 positive children (n = 81) and an equal number of age- and sex- matched controls who were referred to the S. Camillo-Forlanini Pediatric Walk-in Center of Rome. The results of all SARS-CoV-2 nasopharyngeal swabs performed in children aged < 18 years from October 16 to December 19, 2020 were analyzed. RESULTS: School contacts were more frequent in controls than in cases (OR 0.49; 95% CI: 0.3-0.9), while household contacts were higher in cases (OR 5.09; 95% CI: 2.2-12.0). In both cases and controls, school contacts were significantly less frequent, while on the contrary household contacts seemed to be more frequent in nursery school children compared to primary school or middle/high school children. A multivariate logistic regression showed that the probability of being positive to SARS-CoV-2 was significantly lower in children who had school contacts or who had flu symptoms compared to children who had household contacts. Results showed a 30.6% secondary attack rate for household contacts. CONCLUSION: In our study population, the two most frequent reasons for SARS-CoV-2 infection were school and home contacts. The risk of being positive was 5 times lower in children who had school contacts than in children who had household contacts.

Year-to-year variation in attack rates could result in underpowered respiratory syncytial virus vaccine efficacy trials.

OBJECTIVES: Year-to-year variation in respiratory viruses may result in lower attack rates than expected. We aimed to illustrate the impact of year-to-year variation in attack rates on the likelihood of demonstrating vaccine efficacy (VE). STUDY DESIGN AND SETTING: We considered an individually randomized maternal vaccine trial against respiratory syncytial virus (RSV)-associated hospitalizations. For 10 RSV-associated hospitalizations per 1,000 infants, sample size to have 80% power for true VE of 50% and 70% was 9,846 and 4,424 participants. We reported power to show VE for varying attack rates, selected to reflect realistic year-to-year variation using observational studies. Eight scenarios including varying number of countries and seasons were developed to assess the influence of these trial parameters. RESULTS: Including up to three seasons decreased the width of the interquartile range for power. Including more seasons concentrated statistical power closer to 80%. Least powered trials had higher statistical power with more seasons. In all scenarios, at least half of the trials had <80% power. For three-season trials, increasing the sample size by 10% reduced the percentage of underpowered trials to less than one-quarter of trials. CONCLUSION: Year-to-year variation in RSV attack rates should be accounted for during trial design. Mitigation strategies include recruiting over more seasons, or adaptive trial designs.

Symptomatic survey of COVID-19 in the rural health and demographic surveillance site of Maharashtra, India.

Introduction: The COVID-19 epidemic is fast-evolving and restrictions to contain it changes quickly. The secondary attack rate (SAR) indicates the infectiousness at the household level, and it provides a clue of load of infections in the community. Rapid implementation of a large scale, but brief survey provides a nationally representative view of the pandemic's progression and impact as well as the effect of the measures taken to control the spread. Materials and Methods: This cross-sectional study was done for a period of 2 months July-August 2020, in one of the rural health and demographic surveillance system (HDSS) site in India among 11,507 households having 46,571 individuals with the objective to determine the prevalence of the COVID-19 infection and to estimate the family SAR. The data were collected using the mobile phone by calling the head of the households registered under the HDSS. The research tool was created using questions based on the guidelines provided by the Ministry of Health and Family Welfare, India. The interviewers were first trained in data collection. Results: The households of 33,780 individuals were contacted and 33 patients were diagnosed as COVID positive, prevalence rate of 0.1% was thus documented through telephonic survey. The mean age of COVID patients was found to be 37 ± 16 years, and 63% of the diagnosed patients were males, majority of them belonged to above poverty line households. During the survey, 46 individuals reported to have the symptoms suggestive of COVID, fever and cough were the most commonly reported symptoms. The family SAR of 17.2% was documented. Conclusion: Thus to conclude a low COVID-19 prevalence rate of 0.1%, a higher family SAR of 17.2% was reported in the current study. Timely diagnosis and quarantine of close contacts should be continued to be implemented rigorously to prevent the spread of the COVID-19 virus. These efforts will be useful to contain the epidemic before it reaches an alarming level in the rural areas.

Résumé Introduction: L'épidémie de COVID-19 évolue rapidement et les restrictions pour la contenir changent rapidement. Le taux d'attaque secondaire (SAR) indique l'infectiosité au niveau du ménage et fournit un indice de la charge d'infections dans la communauté. La mise en œuvre rapide d'une enquête à grande échelle mais brève fournit une vue représentative à l'échelle nationale de la progression et de l'impact de la pandémie ainsi que de l'effet des mesures prises pour contrôler la propagation. Matériels et Méthodes: cette étude transversale a été réalisée sur une période de 2 mois de juillet à août 2020, dans l'un des sites du système de surveillance sanitaire et démographique en milieu rural (HDSS) en Inde auprès de 11 507 ménages comptant 46 571 individus dans le but de déterminer prévalence de l'infection au COVID-19 et d'estimer le DAS familial. Les données ont été collectées à l'aide du téléphone mobile en appelant le chef de ménage inscrit au HDSS. L'outil de recherche a été créé à l'aide de questions basées sur les directives fournies par le ministère indien de la Santé et du Bien-être familial. Les enquêteurs ont d'abord été formés à la collecte de données. Résultats: les ménages de 33 780 individus ont été contactés et 33 patients ont été diagnostiqués positifs au COVID, un taux de prévalence de 0,1 % a ainsi été documenté par une enquête téléphonique. L'âge moyen des patients COVID était de 37 ± 16 ans, et 63 % des patients diagnostiqués étaient des hommes, la majorité d'entre eux appartenant à des ménages au-dessus du seuil de pauvreté. Au cours de l'enquête, 46 personnes ont déclaré avoir des symptômes évocateurs de COVID, la fièvre et la toux étaient les symptômes les plus fréquemment signalés. Le SAR familial de 17,2 % a été documenté. Conclusion: Ainsi, pour conclure à un faible taux de prévalence de la COVID-19 de 0,1 %, un DAS familial supérieur de 17,2 % a été rapporté dans la présente étude. Le diagnostic rapide et la mise en quarantaine des contacts étroits doivent être poursuivis et mis en œuvre de manière rigoureuse pour empêcher la propagation du virus COVID-19. Ces efforts seront utiles pour contenir l'épidémie avant qu'elle n'atteigne un niveau alarmant dans les zones rurales. Mots-clés: COVID 19, système de surveillance sanitaire et démographique, téléphone portable, prévalence, milieu rural, taux d'attaque secondaire.

SARS-CoV-2 antibody dynamics in blood donors and COVID-19 epidemiology in eight Brazilian state capitals: A serial cross-sectional study.

Background: The COVID-19 situation in Brazil is complex due to large differences in the shape and size of regional epidemics. Understanding these patterns is crucial to understand future outbreaks of SARS-CoV-2 or other respiratory pathogens in the country. Methods: We tested 97,950 blood donation samples for IgG antibodies from March 2020 to March 2021 in 8 of Brazil's most populous cities. Residential postal codes were used to obtain representative samples. Weekly age- and sex-specific seroprevalence were estimated by correcting the crude seroprevalence by test sensitivity, specificity, and antibody waning. Results: The inferred attack rate of SARS-CoV-2 in December 2020, before the Gamma variant of concern (VOC) was dominant, ranged from 19.3% (95% credible interval [CrI] 17.5-21.2%) in Curitiba to 75.0% (95% CrI 70.8-80.3%) in Manaus. Seroprevalence was consistently smaller in women and donors older than 55 years. The age-specific infection fatality rate (IFR) differed between cities and consistently increased with age. The infection hospitalisation rate increased significantly during the Gamma-dominated second wave in Manaus, suggesting increased morbidity of the Gamma VOC compared to previous variants circulating in Manaus. The higher disease penetrance associated with the health system's collapse increased the overall IFR by a minimum factor of 2.91 (95% CrI 2.43-3.53). Conclusions: These results highlight the utility of blood donor serosurveillance to track epidemic maturity and demonstrate demographic and spatial heterogeneity in SARS-CoV-2 spread. Funding: This work was supported by Itaú Unibanco 'Todos pela Saude' program; FAPESP (grants 18/14389-0, 2019/21585-0); Wellcome Trust and Royal Society Sir Henry Dale Fellowship 204311/Z/16/Z; the Gates Foundation (INV- 034540 and INV-034652); REDS-IV-P (grant HHSN268201100007I); the UK Medical Research Council (MR/S0195/1, MR/V038109/1); CAPES; CNPq (304714/2018-6); Fundação Faculdade de Medicina; Programa Inova Fiocruz-CE/Funcap - Edital 01/2020 Number: FIO-0167-00065.01.00/20 SPU N°06531047/2020; JBS - Fazer o bem faz bem.