Serial Intervals and Incubation Periods of SARS-CoV-2 Omicron and Delta Variants, Singapore.

We compared serial intervals and incubation periods for SARS-CoV-2 Omicron BA.1 and BA.2 subvariants and Delta variants in Singapore. Median incubation period was 3 days for BA.1 versus 4 days for Delta. Serial interval was 2 days for BA.1 and 3 days for BA.2 but 4 days for Delta.

Exploring theory-based behavioral interventions promoting COVID-19 prevention and healthcare-seeking for migrant worker men in Singapore: a qualitative study.

BACKGROUND: The first wave of COVID-19 during April to July 2020 in Singapore largely affected the migrant workers living in residential dormitories. A government taskforce working with dormitory operators, employers and non-government agencies came together to deliver behavioral interventions and health care services for migrant worker as dorms were imposed movement restrictions. To fill the research gap in understanding movement restriction experiences of migrant workers, this research seeks to describe dormitory contexts and explore behavior change related to both prevention of transmission as well as healthcare seeking for COVID-19 among male migrant workers. METHODS: With social constructivism as the foundation for this study, 23 telephone interviews were conducted with Bangladeshi and Indian migrant workers. A theory-informed, data-driven conceptual framework, characterized by the "Four Ss": Sensitization, Surveillance, Self-preservation, and Segregation was first generated and later used to frame second-stage, more in-depth, thematic analyses. An effective multipronged approach was documented, persuading migrant workers in our case-study to improve hygiene and follow some safe distancing measures, and adhere to help-seeking when symptomatic. RESULTS: Rapid collective adaptation was demonstrated; it was propped up by effective harnessing of infrastructure and technology. While technology and digital platforms were central to shaping Sensitization for prevention-related behaviors, interpersonal communication, especially peer-sharing, was key to normalizing and accepting healthcare delivery and norms about healthcare seeking. Interpersonal factors particularly supported successful implementation of case-detection Surveillance, stimulating Self-preserving and acceptance of rules, and was found helpful to those Segregated in recovery facilities. In contrast, encouraging prevention-related behaviors relied more heavily on multiple online-platforms, phone-based e-learning/knowledge testing, e-monitoring of behavior, as well as interpersonal exchanges. CONCLUSION: Overall, the findings showed that the conception of the Four Ss helped inform intervention strategies. Anchoring these towards optimal use of technology and harnessing of interpersonal communication for prevention and promotion of healthcare seeking in the planning of future Infectious Disease outbreaks in closed institutional settings is recommended.

Viral Load of SARS-CoV-2 in Respiratory Aerosols Emitted by COVID-19 Patients while Breathing, Talking, and Singing

BackgroundMultiple SARS-CoV-2 superspreading events suggest that aerosols play an important role in driving the COVID-19 pandemic. However, the detailed roles of coarse (>5m) and fine ([≤]5m) respiratory aerosols produced when breathing, talking, and singing are not well-understood. MethodsUsing a G-II exhaled breath collector, we measured viral RNA in coarse and fine respiratory aerosols emitted by COVID-19 patients during 30 minutes of breathing, 15 minutes of talking, and 15 minutes of singing. ResultsAmong the 22 study participants, 13 (59%) emitted detectable levels of SARS-CoV-2 RNA in respiratory aerosols, including 3 asymptomatic patients and 1 presymptomatic patient. Viral loads ranged from 63-5,821 N gene copies per expiratory activity per patient. Patients earlier in illness were more likely to emit detectable RNA, and loads differed significantly between breathing, talking, and singing. The largest proportion of SARS-CoV-2 RNA copies was emitted by singing (53%), followed by talking (41%) and breathing (6%). Overall, fine aerosols constituted 85% of the viral load detected in our study. Virus cultures were negative. ConclusionsFine aerosols produced by talking and singing contain more SARS-CoV-2 copies than coarse aerosols and may play a significant role in the transmission of SARS-CoV-2. Exposure to fine aerosols should be mitigated, especially in indoor environments where airborne transmission of SARS-CoV-2 is likely to occur. Isolating viable SARS-CoV-2 from respiratory aerosol samples remains challenging, and whether this can be more easily accomplished for emerging SARS-CoV-2 variants is an important enquiry for future studies. Key PointsWe sampled respiratory aerosols emitted by COVID-19 patients and discovered that fine aerosols ([≤]5m) generated during talking and singing contain more SARS-CoV-2 copies than coarse aerosols (>5m) and may play a significant role in the transmission of SARS-CoV-2.

Identifying COVID-19 cases in primary care settings

Case identification is an ongoing issue for the COVID-19 epidemic, in particular for outpatient care where physicians must decide which patients to prioritise for further testing. This paper reports tools to classify patients based on symptom profiles based on 236 SARS-CoV-2 positive cases and 564 controls, accounting for the time course of illness at point of assessment. Clinical differentiators of cases and controls were used to derive model-based risk scores. Significant symptoms included abdominal pain, cough, diarrhea, fever, headache, muscle ache, runny nose, sore throat, temperature between 37.5{degrees}C and 37.9{degrees}C, and temperature above 38{degrees}C, but their importance varied by day of illness at assessment. With a high percentile threshold for specificity at 0.95, the baseline model had reasonable sensitivity at 0.67. To further evaluate accuracy of model predictions, we firstly used leave-one-out cross-validation, which confirmed high classification accuracy with an area under the receiver operating characteristic curve of 0.92. For the baseline model, sensitivity decreased to 0.56. Secondly, in a separate ongoing prospective study of 237 COVID-19 and 346 primary care patients presenting with symptoms of acute respiratory infection, the baseline model had a sensitivity of 0.57 and specificity of 0.89, and in retrospective notes review of 100 COVID-19 cases diagnosed in primary care, sensitivity was 0.56. A web-app based tool has been developed for easy implementation as an adjunct to laboratory testing to differentiate COVID-19 positive cases among patients presenting in outpatient settings.

Estimating number of global importations of COVID-19 from Wuhan, risk of transmission outside mainland China and COVID-19 introduction index between countries outside mainland China

BackgroundThe emergence of a novel coronavirus (SARS-CoV-2) in Wuhan, China in early December 2019 has caused widespread transmission within the country, with over 1,000 deaths reported to date. Other countries have since reported coronavirus disease 2019 (COVID-19) importation from China, with some experiencing local transmission and even case importation from countries outside China. We aim to estimate the number of cases imported from Wuhan to each country or territory outside mainland China, and with these estimates assess the risk of onward local transmission and the relative potential of case importation between countries outside China. MethodsWe used the reported number of cases imported from Wuhan and flight data to generate an uncertainty distribution for the estimated number of imported cases from Wuhan to each location outside mainland China. This uncertainty was propagated to quantify the local outbreak risk using a branching process model. A COVID-19 introduction index was derived for each pair of donor and recipient countries, accounting for the local outbreak risk in the donor country and the between- country connectivity. ResultsWe identified 13 countries or territories outside mainland China that may have under-detected COVID-19 importation from Wuhan, such as Thailand and Indonesia. In addition, 16 countries had a local outbreak risk estimate exceeding 50%, including four outside Asia. The COVID-19 introduction index highlights potential locations outside mainland China from which cases may be imported to each recipient country. ConclusionsAs SARS-CoV-2 continues to spread globally, more epicentres may emerge outside China. Hence, it is important for countries to remain alert for the possibilities of viral introduction from other countries outside China, even before local transmission in a source country becomes known.

Do antibody responses to the influenza vaccine persist year-round in the elderly? A systematic review and meta-analysis.

INTRODUCTION: The influenza vaccine is less immunogenic in older than younger adults, and the duration of protection is unclear. Determining if protection persists beyond a typical seasonal epidemic is important for climates where influenza virus activity is year-round. METHODS: A systematic review protocol was developed and registered with PROSPERO [CRD42015023847]. Electronic databases were searched systematically for studies reporting haemagglutination-inhibition (HI) titres 180-360days following vaccination with inactivated trivalent seasonal influenza vaccine, in adults aged ⩾65years. Geometric mean titre (GMT) and seroprotection (HI titre ⩾1:40) at each time point was extracted. A Bayesian model was developed of titre trajectories from pre-vaccination to Day 360. In the meta-analysis, studies were aggregated using a random-effects model to compare pre-vaccination with post-vaccination HI titres at Day 21-42 ('seroconversion'), Day 180 and Day 360. Potential sources of bias were systematically assessed, and heterogeneity explored. RESULTS: 2864 articles were identified in the literature search, of which nineteen met study inclusion/exclusion criteria. Sixteen studies contained analysable data from 2565 subjects. In the Bayesian model, the proportion of subjects seroprotected increased from 41-51% pre-vaccination to 75-78% at seroconversion. Seroprotection subsequently fell below 60% for all serotypes by Day 360: A/H1 42% (95% CI 38-46), A/H3 59% (54-63), B 47% (42-52). The Bayesian model of GMT trajectories revealed a similar pattern. By Day 360, titres were similar to pre-vaccination levels. In the meta-analysis, no significant difference in proportion of subjects seroprotected, 0 (-0.11, 0.11) or in log2GMT 0.30 (-0.02, 0.63) was identified by Day 360 compared with pre-vaccination. The quality of this evidence was limited to moderate on account of significant participant dropout. CONCLUSIONS: The review found consistent evidence that HI antibody responses following influenza vaccination do not reliably persist year-round in older adults. Alternative vaccination strategies could provide clinical benefits in regions where year-round protection is important.

Influenza B outbreak among influenza-vaccinated welfare home residents in Singapore

<p><b>INTRODUCTION</b>Outbreaks of acute respiratory illness occur commonly in long-term care facilities (LTCF), due to the close proximity of residents. Most influenza outbreak reports have been from temperate countries. This study reports an outbreak of influenza B among a highly immunised resident population in a welfare home in tropical Singapore, and discusses vaccine efficacy and the role of acute respiratory illness surveillance for outbreak prevention and control.</p><p><b>MATERIALS AND METHODS</b>During the period from 16 to 21 March 2007, outbreak investigations and active case finding were carried out among residents and nursing staff at the welfare home. Interviews and medical notes review were conducted to obtain epidemiological and clinical data. Hospitalised patients were tested for respiratory pathogens. Further genetic studies were also carried out on positive respiratory samples.</p><p><b>RESULTS</b>The overall clinical attack rate was 9.4% (17/180) in residents and 6.7% (2/30) in staff. All infected residents and staff had received influenza immunisation. Fifteen residents were hospitalised, with 2 developing severe complications. Genetic sequencing revealed that the outbreak strain had an 8.2% amino acid difference from B/Malaysia/2506/2004, the 2006 southern hemisphere influenza vaccine strain, which the residents and staff had earlier received.</p><p><b>CONCLUSIONS</b>A mismatch between the vaccine and circulating influenza virus strains can result in an outbreak in a highly immunised LTCF resident population. Active surveillance for acute respiratory illness in LTCFs could be implemented for rapid detection of antigenic drift. Enhanced infection control and other preventive measures can then be deployed in a timely manner to mitigate the effect of any outbreaks.</p>