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1.
Infect Disord Drug Targets ; 22(4): e170122200309, 2022.
Article in English | MEDLINE | ID: covidwho-1892489

ABSTRACT

Herd immunity can only be achieved when it is extended to the population level. When a sufficiently significant fraction of immune individuals exists in a group, it confers indirect protection from infection to vulnerable individuals. This population-level effect is frequently considered in the context of vaccination programs, which attempt to build herd immunity so that people who cannot be vaccinated, such as the very young or those with impaired immune systems, are nonetheless protected from disease. Clinical signs are at times poor predictor of transmissibility for some infections, such as COVID-19, because asymptomatic hosts can be extremely infectious and contribute to the spread of the virus. COVID-19 is a quickly evolving issue that has been widely spread throughout the world. This article elaborates the idea and goal of herd immunity, the necessary conditions for realizing herd immunity, the restrictive requirements for applying herd immunity, and the obstacles experienced in achieving herd immunity in the context of COVID-19. This mini-article explains the concept and purpose of herd immunization in the context of COVID-19.


Subject(s)
COVID-19 , Immunity, Herd , COVID-19/prevention & control , Humans , Immunization Programs , SARS-CoV-2 , Vaccination
2.
J Econ Theory ; 204: 105501, 2022 Sep.
Article in English | MEDLINE | ID: covidwho-1885904

ABSTRACT

This paper considers a susceptible-infected-recovered type model of infectious diseases, such as COVID-19 or swine flu, in which costly treatment or vaccination confers immunity on recovered individuals. Once immune, individuals indirectly protect the remaining susceptibles, who benefit from a measure of herd immunity. Treatment and vaccination directly induce such herd immunity, which builds up over time. Optimal treatment is shown to involve intervention at early stages of the epidemic, while optimal vaccination may defer intervention to intermediate stages. Thus, while treatment and vaccination have superficial similarities, their effects and desirability at different stages of the epidemic are different. Equilibrium vaccination is qualitatively similar to socially optimal vaccination, while equilibrium treatment differs in nature from socially optimal treatment. The optimal policies are compared to traditional non-economic public health interventions which rely on herd immunity thresholds.

3.
Public Health Challenges ; 1(2):e7, 2022.
Article in English | Wiley | ID: covidwho-1881450

ABSTRACT

The COVID-19 outbreak has had a great impact on the social, economic, and health systems of Thailand. A variety of measures to curb the spread of the disease were implemented since the beginning of the pandemic, including a strict national lockdown protocol. The Thai government aimed to achieve herd immunity through an efficient vaccination programme. Initially, vaccine supply shortage and a lack of vaccine options plagued the health system, but this has since been improved. Continuous monitoring of the situation through research is being carried out to assess the level of immunity among the population whereby the current general recommendation is presently a fourth booster dose for adults. Hurdles towards achieving herd immunity remain. One such issue is the low level of vaccine literacy among those that are unvaccinated or inadequately vaccinated. Another obstacle is the sizeable rate of hesitancy towards getting booster doses. Achieving herd immunity in the Thai population would require multilateral cooperation, improved health promotion to target population groups, such as older adults, and a developed distribution system for those with limited access, such as those in the rural areas.

4.
General Medicine ; 23(6):33-36, 2021.
Article in Bulgarian | EMBASE | ID: covidwho-1880704

ABSTRACT

In order to overcome the challenge of the COVID pandemic, 70% of the population has to develop individual protection, which is formed after getting through the disease or vaccinating oneself. According to sociologists, about 28-30% would like to vaccinate themselves. The purpose of the survey was to analyze the awareness of citizens with regard to vaccination. The methods used are documentary as well as sociological. 420 vaccinated people took part in the opinion poll. Results: 65.8% considers themselves informed about the vaccination, using the media (56.2%) and doctors (45.3%) as their sources. About half of them think that information on the media is not sufficient (55.5%). Almost all (88%) are convinced that measures should be implemented to increase awareness through more information which is specific and provided by experts. Conclusion: In order to reach that number of people (about 3.5 million) in the country which is necessary for creating a protective shield of herd immunity against COVID-19, continuous and purposeful educational and information activities of a greater scope should be carried out among the population.

5.
Nature Communications ; 13(1), 2022.
Article in English | ProQuest Central | ID: covidwho-1877451

ABSTRACT

Determining the duration of immunity induced by booster doses of CoronaVac is crucial for informing recommendations for booster regimens and adjusting immunization strategies. In two single-centre, double-blind, randomised, placebo-controlled phase 2 clinical trials, immunogenicity and safety of four immunization regimens are assessed in adults aged 18 to 59 years and one immunization regimen in adults aged 60 years and older, respectively. Serious adverse events occurring within 6 months after booster doses are recorded as pre-specified secondary endpoints, geometric mean titres (GMTs) of neutralising antibodies one year after the 3-dose schedule immunization and 6 months after the booster doses are assessed as pre-specified exploratory endpoints, GMT fold-decreases in neutralization titres are assessed as post-hoc analyses. Neutralising antibody titres decline approximately 4-fold and 2.5-fold from day 28 to day 180 after third doses in adults aged 18–59 years of age and in adults aged 60 years and older, respectively. No safety concerns are identified during the follow-up period. There are increases in the magnitude and duration of humoral response with homologous booster doses of CoronaVac given 8 months after a primary two-dose immunization series, which could prolong protection and contribute to building our wall of population immunity. Trial number: NCT04352608 and NCT04383574.Following a booster dose of CoronaVac in two single-centre phase 2 clinical trials, the authors show that neutralising antibody titres decline approximately 4-fold and 2.5-fold from day 28 to day 180 in adults aged 18-59 years and in adults aged 60 years and older, respectively.

6.
Euro Surveill ; 27(21)2022 May.
Article in English | MEDLINE | ID: covidwho-1875326

ABSTRACT

BackgroundSARS-CoV-2 emergence was a threat for armed forces. A COVID-19 outbreak occurred on the French aircraft carrier Charles de Gaulle from mid-March to mid-April 2020.AimTo understand how the virus was introduced, circulated then stopped circulation, risk factors for infection and severity, and effectiveness of preventive measures.MethodsWe considered the entire crew as a cohort and collected personal, clinical, biological, and epidemiological data. We performed viral genome sequencing and searched for SARS-CoV-2 in the environment.ResultsThe attack rate was 65% (1,148/1,767); 1,568 (89%) were included. The male:female ratio was 6.9, and median age was 29 years (IQR: 24-36). We examined four clinical profiles: asymptomatic (13.0%), non-specific symptomatic (8.1%), specific symptomatic (76.3%), and severe (i.e. requiring oxygen therapy, 2.6%). Active smoking was not associated with severe COVID-19; age and obesity were risk factors. The instantaneous reproduction rate (Rt) and viral sequencing suggested several introductions of the virus with 4 of 5 introduced strains from within France, with an acceleration of Rt when lifting preventive measures. Physical distancing prevented infection (adjusted OR: 0.55; 95% CI: 0.40-0.76). Transmission may have stopped when the proportion of infected personnel was large enough to prevent circulation (65%; 95% CI: 62-68).ConclusionNon-specific clinical pictures of COVID-19 delayed detection of the outbreak. The lack of an isolation ward made it difficult to manage transmission; the outbreak spread until a protective threshold was reached. Physical distancing was effective when applied. Early surveillance with adapted prevention measures should prevent such an outbreak.


Subject(s)
COVID-19 , Adult , Aircraft , COVID-19/epidemiology , Disease Outbreaks , Female , Humans , Male , Retrospective Studies , SARS-CoV-2/genetics
7.
Ciencia & Saude Coletiva ; 27(5):1843-1848, 2022.
Article in English | Web of Science | ID: covidwho-1869238

ABSTRACT

Although communicable diseases affect our bodies, they occur in a society that interprets and gives them meaning. Herd immunity provides the body protection;however, long-term protection requires shifts in the way people interpret and respond to disease, cultural transformation that enables the development of the knowledge, habits and skills that make herd immunity feasible and sustainable. Herd culture allows individuals to protect themselves and restrict their liberty in order to protect others;it is a form of exercising positive liberty and a necessary complement to herd immunity in a democratic society.

8.
Rheumatology (United Kingdom) ; 61(SUPPL 1):i54, 2022.
Article in English | EMBASE | ID: covidwho-1868380

ABSTRACT

Background/Aims According to newspaper Bernama, 6.5% of adolescents in Malaysia aged between 12 and 17 have completed their vaccination and 89.7% of the adult population have completed theirs as of 9th October 2021. The acceptance of patients with rheumatic diseases on Covid-19 vaccination are crucial in the successful long-term protection against COVID-19 infection. We conducted a phone survey to determine the acceptance of COVID-19 vaccination amongst adolescents with underlying rheumatic disease. Methods This was a phone survey. The electronic medical records of all rheumatology patients follow up in rheumatology clinic Hospital Sultan Ismail, Malaysia from 2019 to 2021 were reviewed and patients with the age group between 12 to 21 were identified. Demographic data, diagnosis of the disease and outcome of the survey were collected and analysed. Results Phone survey was done after data extracted from medical records. For those under the age of 18, guardian of the patients was interviewed. A total of 50 patients were identified. Most of the patients were female (46/50) and majority of them were Malay (33/50). This was followed by Chinese (10/50), Indian (4/50) and others (3/50). The mean age group was 18 (range from 13 to 21). 36 of them were having systemic lupus erythematosus (SLE), 5 of them were having juvenile idiopathic arthritis (JIA) ,2 of them were having psoriatic arthritis (PSA) and another 2 of them were having rheumatoid arthritis (RA), followed by RA overlapped SLE, juvenile dermatomyositis, Henoch-Schönlein purpura, SLE overlapped with JIA and mixed connective tissue disease about 1 each respectively. Majority of them patients are keen or already completed COVID-19 vaccination with the acceptance rate of as high as 92% (46/50). Only 8% of them are not keen for vaccination with the only reason of worrying the risk of myocarditis post vaccination (1 SLE patient and 1 PSA patient). Conclusion The overall acceptance rate of COVID-19 vaccination amongst adolescents with rheumatic diseases are very encouraging with the percentage of>90% despite lacking knowledge about vaccination for COVID-19. This result can assist our Ministry of Health in planning for future battles to improve vaccine uptake that hopefully can lead to herd immunity against COVID-19 infection.

9.
Rheumatology (United Kingdom) ; 61(SUPPL 1):i51, 2022.
Article in English | EMBASE | ID: covidwho-1868374

ABSTRACT

Background/Aims Vaccine-associated autoimmunity is not infrequent, pertaining to either the cross-reaction between antigens or the action of adjuvant. This issue is more inexplicable to the COVID-19 vaccine, because of nucleic acid formulation and the hastened development process inflicted by the urgent pandemic condition. Here we are presenting a young patient who developed a significant abnormal autoimmune profile immediately post covid vaccination. Methods A 31-year-old IT engineer was referred to Rheumatology with postvaccine arthralgia. He had a history of recent aortic root aneurysm repair after having chest pain on exertion. Echocardiography showed dilated aortic root with significant aortic regurgitation, CT aortogram confirmed spiral type A dissection. He underwent an emergency cardiothoracic surgery in October 2020, followed by an uneventful recovery. He received the first dose of Pfizer COVID-19 vaccine on 2nd February, the very next day he developed painful ankles, knees, left hip, and right shoulder. Blood tests showed elevated CRP of 45, ESR 34, rheumatoid factor positive at 92, anti-CCP >340, ANA 13, ds-DNA 202, U1RNP positive, anti-SM antibody positive, Ro and La antibodies positive, antiJo1 antibody positive, with normal complements. He denied any swelling of the joints. No history of hair loss, photosensitive skin rashes, Raynaud's, sicca symptoms, oro-genital ulceration, or cracking of the skin. There were no constitutional symptoms, chest pain, or bowel issues. He was previously labeled as asthmatic, which is stable after surgery. He doesn't smoke or drinks alcohol. There was no family history of autoimmune conditions. On examination, he has tenderness across both hands and wrists with palmar erythema but no synovitis. He has painful right shoulder abduction with left hip pain on flexion and extension. Cardiovascular and GI examination was unremarkable apart from sternotomy scar and metallic valvular heart sounds. His dipstick urinalysis was negative for blood and protein. In recent x-rays hands and feet were normal. We agreed on a trial a tapering course of prednisolone started with 20mg daily. Three weeks later in follow-up, he reported partial response to steroids. His inflammatory markers were coming down. We have started azathioprine as a steroid-sparing agent. Results This gentleman with negative autoimmune screening prior to cardiothoracic surgery expressed florid newly detected autoantibodies straightaway after the COVID-19 vaccine. This is suggestive of undifferentiated connective tissue disease with the likelihood of overlap syndrome between rheumatoid arthritis and SLE. Conclusion COVID-19 vaccination showed a beacon of light to end the pandemic by achieving herd immunity. There is an excusable socioeconomic rush towards mass vaccination without long-term safety analysis, however, it is also crucial that any vaccine licensing process should entail meticulous scrutiny of the human proteome against vaccine peptide sequences. This will minimize the risks of acute autoimmune reactions to inoculation and future chronic autoimmune pathology.

10.
Hum Vaccin Immunother ; : 2072144, 2022 May 25.
Article in English | MEDLINE | ID: covidwho-1864929

ABSTRACT

Vaccine hesitancy against COVID-19 is prevalent. This study aimed to identify the factors associated with COVID-19 vaccination compliance among adults in Hong Kong. An online survey was conducted during an early stage of community-based COVID-19 vaccination campaign in Hong Kong. The questionnaire consisted of vaccine status, sociodemographic information, risk perception of being infected by COVID-19, and exposure to confirmed COVID cases, as well as items on sleep and mental health. The association between these variables and vaccine hesitancy was analyzed. Among the 883 participants (67.5% females, 54.5% aged 18-39), 30.6% had low vaccine hesitancy, 27.4% had high vaccine hesitancy, and 27.5% had vaccine rejection. The likelihood of having high vaccine hesitancy was higher among young (adjusted odds ratio [aOR] = 2.99; 95% confidence interval [CI]: 1.23-7.30) and middle-aged respondents (aOR = 2.99; 95% CI: 1.07-5.47) than among old respondents. Moreover, those who were married (aOR = 0.51; 95% CI: 0.29-0.88), had a full-time job (aOR = 0.55; 95% CI: 0.29-0.88), and had a greater confidence in the government (aOR = 0.68; 95% CI: 0.54-0.86) were less likely to exhibit vaccine hesitancy. Our findings showed that the prevalence of vaccine hesitancy and vaccine resistance were high. Policy makers need specific strategies to target those who may have a high risk of vaccine hesitancy and resistance.

11.
Quantitative Biology ; 9(3):304-316, 2021.
Article in English | ProQuest Central | ID: covidwho-1863420

ABSTRACT

Background: The availability of vaccines provides a promising solution to contain the COVID-19 pandemic. However, it remains unclear whether the large-scale vaccination can succeed in containing the COVID-19 pandemic and how soon. We developed an epidemiological model named SUVQC (Suceptible-Unquarantined-Vaccined-Quarantined-Confirmed) to quantitatively analyze and predict the epidemic dynamics of COVID-19 under vaccination. Methods: In addition to the impact of non-pharmaceutical interventions (NPIs), our model explicitly parameterizes key factors related to vaccination, including the duration of immunity, vaccine efficacy, and daily vaccination rate etc. The model was applied to the daily reported numbers of confirmed cases of Israel and the USA to explore and predict trends under vaccination based on their current epidemic statuses and intervention measures. We further provided a formula for designing a practical vaccination strategy, which simultaneously considers the effects of the basic reproductive number of COVID-19, intensity of NPIs, duration of immunological memory after vaccination, vaccine efficacy and daily vaccination rate. Results: In Israel, 53.83% of the population is fully vaccinated, and under the current NPI intensity and vaccination scheme, the pandemic is predicted to end between May 14, 2021, and May 16, 2021, assuming immunity persists for 180 days to 365 days. If NPIs are not implemented after March 24, 2021, the pandemic will end later, between July 4, 2021, and August 26, 2021. For the USA, if we assume the current vaccination rate (0.268% per day) and intensity of NPIs, the pandemic will end between January 20, 2022, and October 19, 2024, assuming immunity persists for 180 days to 365 days. However, assuming immunity persists for 180 days and no NPIs are implemented, the pandemic will not end and instead reach an equilibrium state, with a proportion of the population remaining actively infected. Conclusions: Overall, the daily vaccination rate should be decided according to vaccine efficacy and immunity duration to achieve herd immunity. In some situations, vaccination alone cannot stop the pandemic, and NPIs are necessary to supplement vaccination and accelerate the end of the pandemic. Considering that vaccine efficacy and duration of immunity may be reduced for new mutant strains, it is necessary to remain cautiously optimistic about the prospect of ending the pandemic under vaccination.

12.
Vaccines (Basel) ; 10(5)2022 May 08.
Article in English | MEDLINE | ID: covidwho-1862944

ABSTRACT

The pandemic associated with SARS-CoV-2 is a worldwide public health challenge. The WHO has proposed to achieve 70% COVID-19 vaccination coverage in all countries by mid-2022. Nevertheless, the prevention strategy based on COVID-19 vaccination and other applied prevention measures has not been sufficient to prevent SARS-CoV-2 epidemic waves. This study assessed the vaccination coverage that would be required to establish herd immunity against SARS-CoV-2, taking into account virus transmissibility (Ro values from 1.1 to 10) and COVID-19 vaccination effectiveness. The study found that high percentages of vaccination coverage and high levels of vaccination effectiveness are necessary to block the transmission of Omicron and other SARS-CoV-2 variants with greater infectious capacity. COVID-19 vaccination programs could establish herd immunity against SARS-CoV-2, with Ro values ranging from 3 to 10 and levels of COVID-19 vaccination effectiveness of 70-100%. Factors reducing COVID-19 vaccination effectiveness (emergent variants, infections among vaccinated individuals, high risk individuals) and factors increasing SARS-CoV-2 transmissibility (close settings) increased the percentages of vaccination coverage that would be required to establish herd immunity. Two measures should be implemented to establish herd immunity against SARS-CoV-2: (1) achieve ≥ 90% COVID-19 vaccination coverage in all countries worldwide, and (2) increase the effectiveness of COVID-19 vaccines in preventing Omicron infection to at least 88%.

13.
Embase; 2022.
Preprint in English | EMBASE | ID: ppcovidwho-337483

ABSTRACT

Face masking in current COVID-19 pandemic seems to be a deceivingly simple decision-making problem due to its multifaceted nature. Questions arising from masking span biomedicine, epidemiology, physics, and human behaviors. While science has shown masks work generally, human behaviors (particularly under influences of politics) complicate the problem significantly given science generally assumes rationality and our minds are not always rational and/or honest. Minding minds, a legitimate concern, can also make masking legitimately confusing. To disentangle the potential confusions, particularly, the ramifications of irrationality and dishonesty, here we resort to evolutionary game theory. Specifically, we formulate and analyze the masking problem with a fictitious pair of young lovers, Alice and Bob, as a Sir Philip Sydney (SPS) evolutionary game, inspired by the handicap principle in evolutionary biology and cryptography figures in computer science. With the proposed ABD (Alice and Bob’s dating dilemma) as an asymmetric four-by-four strategic-form game, 16 strategic interactions were identified, and six of which may reach equilibriums with different characteristics such as separating, pooling, and polymorphic hybrid, being Nash, evolutionarily stable or neutrally stable. The six equilibrium types seem to mirror the diverse behaviors of mask believers, skeptics, converted, universal masking, voluntarily masking, coexisted and/or divided world of believers and skeptics. We suggest that the apparently simple ABD game is sufficiently general not only for studying masking policies for populations (via replicator dynamics), but also for investigating other complex decision-making problems with COVID-19 pandemic including lockdown vs. reopening, herd immunity vs. quarantines, and aggressive tracing vs. privacy protection.

14.
Int J Semiot Law ; : 1-19, 2021 Jul 10.
Article in English | MEDLINE | ID: covidwho-1859074

ABSTRACT

Undoubtedly and unfortunately, COVID-19 pandemic has been politicized in media see Abbas (Int J Semiot Law, 2020), Rui Zhang (Media Asia 48:89-107, 2021). Although vaccines play a crucial role in eliminating the pandemic, they have been politicized by media. This article aims to show how COVID-19 vaccines are politicized in the press. The article collects some selected reports on vaccines taken from American and Chinese media. The reports are analyzed according to an analytical framework suggested by the researcher. The framework and data collection and description are clearly presented in the method section. Based on data analysis, the article shows that COVID-19 vaccines have been politicized. The study recommends that diseases and vaccines should not be politicized. In other words, we should respect and trust science and our scientists for no other purpose than to reach herd immunity and overcome a dangerous pandemic that has taken and is still taking thousands of innocent lives.

15.
29th Iranian Conference on Electrical Engineering (ICEE) ; : 579-585, 2021.
Article in English | Web of Science | ID: covidwho-1853439

ABSTRACT

Intrusion Detection System (IDS) is considered as one of the essential components of a secure network. Due to the high number of network packet features, one of the major problems of IDS is false intrusion alerts and low intrusion detection rates. Feature selection removes all redundant or irrelevant features among the various features of network packets. For this reason, it plays a pivotal role in overcoming the mentioned problems and can improve the accuracy of intrusion detection system. In this paper, a new human-inspired optimization algorithm called coronavirus herd immunity optimizer (CHIO) is proposed for feature selection in IDS. CHIO is able to select the optimal subset of features from numerous features without affecting system performance. In order to select the feature, two types of classifiers, K-Nearest Neighbor (KNN) and Artificial Neural Network (ANN), are used to obtain the accuracy of intrusion detection. In addition, the ANN classifier is trained with the classic Gradient Descent ( GD) method as well as the two intelligent methods Artificial Bee Colony (ABC) and Harmony Search (HS). In order to demonstrate the performance, our method is tested on 20% of NSL-KDD and its results are reported and compared to other studies. The proposed method has been able to achieve better performance in terms of intrusion detection accuracy and number of features compared to similar works.

16.
Distinktion-Journal of Social Theory ; : 14, 2022.
Article in English | Web of Science | ID: covidwho-1852678

ABSTRACT

The purpose of this article is in threefold. First, it focuses on the workings and operations of the biopolitical economy. Second, it explores how the pandemic has exposed the thanatopolitical tendency of neoliberal capitalism, particularly in the form of herd immunity. Herd immunity deploys death as one of the instruments, making plain that the valuation of life is based on its sacrificability to capital. The final part engages with Roberto Esposito's affirmative biopolitical perspective that strives to avoid the thanatopolitical tendency Agamben (over-)emphasized. I claim that while Esposito's affirmative biopolitical perspective puts pressure on the thanatopolitical position, it could nevertheless be invoked for the reconstitution or reconceptualization of the future commons.

17.
Epidemics ; 39: 100581, 2022 06.
Article in English | MEDLINE | ID: covidwho-1851044

ABSTRACT

We present a country specific method to calculate the COVID-19 vaccination coverage needed for herd immunity by considering age structure, age group-specific contact patterns, relative infectivity and susceptibility of children to adults, vaccination effectiveness and seroprevalence prior to vaccination. We find that across all six countries, vaccination of adults age 60 and above has little impact on Reff and this is could be due to the smaller number of contacts between this age group and the rest of the population according to the contact matrices used. If R0 is above 6, herd immunity by vaccine alone is unattainable for most countries either if vaccination is only available for adults or that vaccine effectiveness is lower at 65% against symptomatic infections. In this situation, additional control measures, booster shots, if they improve protection against infection, or the extension of vaccination to children, are required. For a highly transmissible variant with R0 up to 8, herd immunity is possible for all countries and for all four scenarios of varying relative infectivity and susceptibility of children compared to adults, if vaccine effectiveness is very high at 95% against symptomatic infections and that high vaccination coverage is achieved for both adults and children. In addition, we show that the effective reproduction number will vary between countries even if the same proportion of the population is vaccinated, depending on the demographics, the contact rates and the previous pre-vaccination seroprevalence in the country. This therefore means that care must be taken in extrapolating population level impacts of certain vaccine coverages from one country to another.


Subject(s)
COVID-19 , Immunity, Herd , Adult , COVID-19/epidemiology , COVID-19/prevention & control , COVID-19 Vaccines , Child , Humans , Middle Aged , Seroepidemiologic Studies , Vaccination/methods , Vaccination Coverage
18.
IEEE Access ; 2022.
Article in English | Scopus | ID: covidwho-1840229

ABSTRACT

The effectiveness of the first dose of vaccination for COVID-19 is different from that of the second dose;therefore, in several studies, various mathematical models that can represent the states of the first and second vaccination doses have been developed. Using the results of these studies and considering the effects of the first and second vaccination doses, we can simulate the spread of infectious diseases. The susceptible-infected-recovered-vaccination1-vaccination2-death (SIRVVD) model is one of the proposed mathematical models;however, it has not been sufficiently theoretically analyzed. Therefore, we obtained an analytical expression for the number of infected persons by considering the numbers of susceptible and vaccinated persons as parameters. We used the solution to determine the target vaccination rate for decreasing the infection numbers of the COVID-19 Delta variant (B.1.617) in Japan. Furthermore, we investigated the target vaccination rates for cases with strong or weak variants by comparing with the COVID-19 Delta variant (B.1.617). This study contributes to the mathematical development of the SIRVVD model and provides insights into the target vaccination rate for decreasing the number of infections. Author

19.
Embase; 2021.
Preprint in English | EMBASE | ID: ppcovidwho-336223

ABSTRACT

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) have been key drivers of new coronavirus disease 2019 (COVID-19) pandemic waves. To better understand variant epidemiologic characteristics, here we apply a model-inference system to reconstruct SARS-CoV-2 transmission dynamics in South Africa, a country that has experienced three VOC pandemic waves (i.e. Beta, Delta, and Omicron). We estimate key epidemiologic quantities in each of the nine South African provinces during March 2020 - Feb 2022, while accounting for changing detection rates, infection seasonality, nonpharmaceutical interventions, and vaccination. Model validation shows that estimated underlying infection rates and key parameters (e.g., infection-detection rate and infection-fatality risk) are in line with independent epidemiological data and investigations. In addition, retrospective predictions capture pandemic trajectories beyond the model training period. These detailed, validated model-inference estimates thus enable quantification of both the immune erosion potential and transmissibility of three major SARS-CoV-2 VOCs, i.e., Beta, Delta, and Omicron. These findings help elucidate changing COVID-19 dynamics and inform future public health planning.

20.
Embase; 2021.
Preprint in English | EMBASE | ID: ppcovidwho-335918

ABSTRACT

Introduction The infection-fatality rate (IFR) of COVID-19 has been carefully measured and analyzed in high-income countries, whereas there has been no systematic analysis of age-specific seroprevalence or IFR for developing countries. Methods We systematically reviewed the literature to identify all COVID-19 serology studies in developing countries that were conducted using population representative samples collected by early 2021. For each of the antibody assays used in these serology studies, we identified data on assay characteristics, including the extent of seroreversion over time. We analyzed the serology data using a Bayesian model that incorporates conventional sampling uncertainty as well as uncertainties about assay sensitivity and specificity. We then calculated IFRs using individual case reports or aggregated public health updates, including age-specific estimates whenever feasible. Results Seroprevalence in many developing country locations was markedly higher than in high-income countries. In most locations, seroprevalence among older adults was similar to that of younger age cohorts, underscoring the limited capacity that these nations have to protect older age groups. Age-specific IFRs were roughly 2x higher than in high-income countries. The median value of the population IFR was about 0.5%, similar to that of high-income countries, because disparities in healthcare access were roughly offset by differences in population age structure. Conclusion The burden of COVID-19 is far higher in developing countries than in high-income countries, reflecting a combination of elevated transmission to middle-aged and older adults as well as limited access to adequate healthcare. These results underscore the critical need to accelerate the provision of vaccine doses to populations in developing countries.

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