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1.
Viral Immunol ; 36(5): 318-330, 2023 Jun.
Article in English | MEDLINE | ID: covidwho-2321739

ABSTRACT

This study aims to analyze the achievements of coronavirus disease-2019 (COVID-19) vaccination in five provinces in Indonesia, North Maluku, West Sulawesi, Maluku, West Papua, and Papua. Furthermore, to establish herd immunity in the new normal perspective. Vaccination is important because it is an effective way to build immunity. This method uses qualitative research with a Qualitative Data Analysis Software (QDAS) approach. The source of data was obtained from the official website of the government, the ministry of health, in the category of areas with low vaccination achievement, and data were also obtained by capturing news in credible official media to find the cause of the low vaccination rate in the community. The data analyst uses NVivo12 software to code and visualizes data in graphs, images, and word clouds. The findings of this study indicate that in five provinces in Indonesia, North Maluku (68%), West Sulawesi (76%), Maluku (66%), West Papua (62%), and Papua (41%), the achievement of vaccination implementation is still relatively low. Due to doubts in the community about the status of the vaccine, information and communication education from the government have not been optimal; the environment and geography vary, so it becomes an obstacle in carrying out vaccination.


Subject(s)
COVID-19 Vaccines , COVID-19 , Humans , Indonesia/epidemiology , Immunity, Herd , COVID-19/prevention & control , Vaccination
2.
Vaccine ; 41(25): 3683-3687, 2023 06 07.
Article in English | MEDLINE | ID: covidwho-2313647

ABSTRACT

Parental hesitancy poses a serious threat to the success of the COVID-19 childhood vaccination campaign. We investigate whether adults' opinions on childhood vaccination can be influenced via two survey experiments in Italy (n = 3,633 participants) and the UK (n = 3,314 participants). Respondents were randomly assigned to: a "risk treatment" that highlighted the potential risks of COVID-19 to a child, a "herd immunity treatment" that emphasized the community benefits of pediatric vaccination, or a control message. Participants' probability of supporting COVID-19 childhood vaccination was then assessed on a 0-100 scale. We find that the "risk treatment" reduced the proportion of Italian parents strongly against vaccination by up to 29.6 %, while increasing the proportion of neutral parents by up to 45.0 %. The "herd immunity treatment", instead, was only effective among non-parents, resulting in a lower proportion of individuals against pediatric vaccination and a higher proportion of individuals in favor (both shifted by around 20 %).


Subject(s)
COVID-19 , Adult , Child , Humans , COVID-19/prevention & control , Immunity, Herd , Immunization Programs , Italy/epidemiology , Vaccination
3.
Epidemiol Health ; 43: e2021054, 2021.
Article in English | MEDLINE | ID: covidwho-2274737

ABSTRACT

Vaccination is considered to be the most effective measure for preventing the spread of coronavirus disease 2019 (COVID-19). Many countries, including of Korea, are focusing on achieving herd immunity with the goal of reaching a vaccination rate of 70-80%. However, achieving herd immunity does not mean eradicating COVID-19, and the following challenges can occur in the process of achieving herd immunity. First, as the vaccination rate is likely to slow down over time, it is necessary to promote the benefits of vaccination through risk communication strategies and provide incentives for those who have been vaccinated. Second, a booster dose may be required depending on future studies on vaccine-induced immunity. Third, since variants capable of evading immunity and with higher transmissibility can emerge, rapid contract tracing and regular community genomic surveillance could help mitigate the impact of new variants. When the impact of COVID-19 is controlled to the level of seasonal influenza, the current public health measures that have been strictly imposed on society since the beginning of the pandemic will no longer be needed. The overall response strategy to COVID-19 will need to change accordingly, based on evaluations of the level of population immunity. These changes will include more efficient and targeted contact tracing and eased quarantine measures for vaccinated close contacts and travelers. Mask wearing and a minimum of social distancing will still be required in the journey towards the end of the pandemic. The COVID-19 pandemic will end, but the virus will not disappear.


Subject(s)
COVID-19 Vaccines/administration & dosage , COVID-19/prevention & control , Immunity, Herd , Pandemics/prevention & control , Vaccination/statistics & numerical data , COVID-19/epidemiology , Contact Tracing , Humans , Quarantine , Republic of Korea/epidemiology
5.
Curr Opin Infect Dis ; 36(3): 171-176, 2023 06 01.
Article in English | MEDLINE | ID: covidwho-2282574

ABSTRACT

PURPOSE OF REVIEW: This review summarizes the general concepts of innate and acquired immunity, including vaccine use and hesitancy, as they relate to reduction of the global burden of highly communicable infectious diseases. RECENT FINDINGS: Vaccination to increase herd immunity remains the cornerstone of disease prevention worldwide yet global vaccination goals are not being met. Modern obstacles to vaccine acceptance include hesitancy, reduced altruistic intentions, impact of COVID-19, distrust of science and governmental agencies as well as recent geopolitical and environmental disasters. Together, such barriers have negatively impacted immunization rates worldwide, resulting in epidemics and pandemics of serious life-threatening infections from vaccine-preventable diseases, especially those affecting children. In addition, pathogens thought to be controlled or eradicated are reemerging with new genetic traits, making them more able to evade natural and acquired immunity, including that induced by available vaccines. Lastly, many serious and widespread infectious diseases await development and utilization of efficacious vaccines. SUMMARY: The global burden of communicable diseases remains high, necessitating continued pathogen surveillance as well as vaccine development, deployment and continued efficacy testing. Equally important is the need to educate aggressively the people and their leaders on the benefits of vaccination to the individual, local community and the human population as a whole.


Subject(s)
COVID-19 , Communicable Diseases , Vaccines , Child , Humans , COVID-19/epidemiology , COVID-19/prevention & control , Pandemics/prevention & control , Immunity, Herd , Communicable Diseases/epidemiology , Vaccination , Adaptive Immunity
7.
Expert Opin Drug Deliv ; 20(4): 489-506, 2023 04.
Article in English | MEDLINE | ID: covidwho-2263661

ABSTRACT

INTRODUCTION: In November 2019, the idea of a zoonotic virus crossing over to human transmission in a seafood market in Wuhan, China, and then soaring across the globe to claim over 6.3 million lives and persisting to date, seemed more like wild science fiction than a future reality. As the SARS-CoV-2 pandemic continues, it is important to hallmark the imprints the pandemic has made on science. AREAS COVERED: This review covers the biology of SARS-CoV-2, vaccine formulations and trials, the concept of 'herd resistance,' and the vaccination divide. EXPERT OPINION: The SARS-CoV-2 pandemic has changed the landscape of medicine. The rapid approval of SARS-CoV-2 vaccines has changed the culture of drug development and clinical approvals. This change is already leading to more accelerated trials. The RNA vaccines have opened the market for nucleic acid therapies and the applications are limitless - from cancer to influenza. A phenomenon that has occurred is that the low efficacy of current vaccines and the rapid mutation rate of the virus is preventing herd immunity from being attained. Instead, herd resistance is being acquired. Even with future, more effective vaccines, anti-vaccination attitudes will continue to challenge the quest for SARS-CoV-2 herd immunity.


Subject(s)
COVID-19 , Nucleic Acids , Humans , Pandemics/prevention & control , SARS-CoV-2 , COVID-19 Vaccines , Immunity, Herd , Nanomedicine , COVID-19/prevention & control
8.
Soc Sci Med ; 323: 115854, 2023 04.
Article in English | MEDLINE | ID: covidwho-2265209

ABSTRACT

COVID-19 vaccine hesitancy poses a global health threat by potentially delaying the attainment of herd immunity to attenuate infection and transmission. Most governments across the world are engrossed with formulating strategies to surmount conservative group behavior such as vaccine hesitancy typical under risky and uncertain situations such as in the case of COVID-19. This paper examines herding behavior in vaccine hesitancy with a special focus on the moderating role of household access to health information from village health workers under different risk perceptions. We use the 2021 Zimbabwe Vulnerability Assessment Committee cross-section household national survey consisting of 13, 583 valid observations. Our major findings indicate that herding behavior plays a role in rural households' hesitancy to COVID-19 vaccine inoculation. Furthermore, whilst access to health information from village health workers reduces herding behavior in vaccine hesitancy, it does so more when the household perceives itself to be at high risk of contracting COVID-19. Analysing herding behavior in vaccine hesitancy can help policymakers develop more targeted vaccination strategies, such as promoting access to health information through channels like village health workers, especially for households at high risk of contracting COVID-19.


Subject(s)
COVID-19 Vaccines , COVID-19 , Humans , Community Health Workers , COVID-19/epidemiology , COVID-19/prevention & control , COVID-19 Vaccines/therapeutic use , Government , Vaccination , Zimbabwe/epidemiology , Vaccination Hesitancy , Immunity, Herd
9.
PLoS One ; 18(2): e0279454, 2023.
Article in English | MEDLINE | ID: covidwho-2239538

ABSTRACT

The unfolding of the COVID-19 pandemic has been very difficult to predict using mathematical models for infectious diseases. While it has been demonstrated that variations in susceptibility have a damping effect on key quantities such as the incidence peak, the herd-immunity threshold and the final size of the pandemic, this complex phenomenon is almost impossible to measure or quantify, and it remains unclear how to incorporate it for modeling and prediction. In this work we show that, from a modeling perspective, variability in susceptibility on an individual level is equivalent with a fraction θ of the population having an "artificial" sterilizing immunity. We also derive novel formulas for the herd-immunity threshold and the final size of the pandemic, and show that these values are substantially lower than predicted by the classical formulas, in the presence of variable susceptibility. In the particular case of SARS-CoV-2, there is by now undoubtedly variable susceptibility due to waning immunity from both vaccines and previous infections, and our findings may be used to greatly simplify models. If such variations were also present prior to the first wave, as indicated by a number of studies, these findings can help explain why the magnitude of the initial waves of SARS-CoV-2 was relatively low, compared to what one may have expected based on standard models.


Subject(s)
COVID-19 , Communicable Diseases , Vaccines , Humans , COVID-19/epidemiology , SARS-CoV-2 , Pandemics/prevention & control , Communicable Diseases/epidemiology , Immunity, Herd
10.
Glob Health Res Policy ; 8(1): 2, 2023 02 01.
Article in English | MEDLINE | ID: covidwho-2232760

ABSTRACT

South America, once an epicenter of COVID-19, has stayed on the road of continued management of the pandemic. The region initially struggled to cope with the pandemic as it experienced spiraling numbers of infections and overwhelmed public health systems. South America has risen in its pandemic response to be the region with the highest global vaccination rate. The region posed a strong vaccination drive, with over 76% of its population fully vaccinated with the initial protocol. South America leveraged its deeply rooted vaccination culture and public health confidence among its population. Herd immunity is an integral concept in population infectious disease management. Attaining herd immunity is presently not feasible with available vaccines, but the high vaccination rate in the region depicts the acceptance of vaccination as a strategy for population protection. The availability of effective transmission-blocking vaccines, the continuous implementation of strategies that will enable the undisrupted supply of the vaccines, equity in access to the vaccines, improved vaccine acceptance, and trust in the vaccination and public health systems will help shepherd the region towards herd immunity. Local vaccine production backed with investment in infrastructure and international collaboration for research and knowledge development will also drive population safety.


Subject(s)
COVID-19 , Vaccines , Humans , COVID-19/epidemiology , COVID-19/prevention & control , Immunity, Herd , Vaccination , South America
11.
J Public Health (Oxf) ; 44(4): e606-e607, 2022 Dec 01.
Article in English | MEDLINE | ID: covidwho-2190204

ABSTRACT

The concept of herd immunity during the coronavirus disease 2019 is constantly changing. The World Health Organization's current focus is on vaccination. With ties to the bioethics of autonomy and exemptions to mandatory vaccinations, the problem is that moral conservatism tends not to cooperate in the rollouts. Radical means can be applied not just to the concept but also its application, emphasizing the need to depart from conservative hindrances to public health.


Subject(s)
Bioethics , COVID-19 , Humans , Immunity, Herd , Vaccination , Politics
12.
Sci Rep ; 13(1): 763, 2023 01 14.
Article in English | MEDLINE | ID: covidwho-2186093

ABSTRACT

The death rate from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in 2022 was lower than the death rate in 2021, when the infection rate increased. Hybrid immunity provided by a combination of vaccination and infection, including asymptomatic infection, may confer effective protection against death. We explored the combined effect of asymptomatic infection and hybrid immunity by studying T-cell and antibody responses against SARS-CoV-2 among individuals treated in home health care services 6 months after SARS-CoV-2 exposure. Asymptomatic SARS-CoV-2 infection was demonstrated in 24.4% of close contacts. The levels of immunity were not different between patients and close contacts. Anti-RBD IgG against SARS-CoV-2 increased in a dose-dependent manner with the number of vaccine doses. Interestingly, the T-cell response decreased soon after a booster dose of vaccine. Asymptomatic SARS-CoV-2 infection could not enhance immunity against SARS-CoV-2 among vaccinated close contacts. Full vaccination was crucial to provide hybrid immunity. However, when designing vaccine strategies, T-cell exhaustion after multiple vaccinations should be considered.


Subject(s)
COVID-19 , Home Care Services , Humans , SARS-CoV-2 , Asymptomatic Infections , Immunity, Herd , Vaccination , Antibodies, Viral
13.
Clin Respir J ; 16(11): 708-716, 2022 Nov.
Article in English | MEDLINE | ID: covidwho-2052356

ABSTRACT

Coronavirus disease 2019 (COVID-19), the highly contagious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide with millions of cases and more than 5 million deaths to date. SARS-CoV-2 has caused serious damage all over the world with many countries experiencing the third or the fourth wave of the viral disease outbreaks, mainly due to the emergence of mutant variants. Those who unvaccinated remain most vulnerable to COVID-19 and its variants. COVID-19 vaccination, along with prevention strategies, is a critical measure to defense against the disease. COVID-19 vaccination can reduce the spread of virus and help protect susceptible population. Although herd immunity might not be realized solely by vaccination, COVID-19 vaccines have been proved to be effective in reducing the risk of severe disease, hospitalization, and even death. It is recommended that people get vaccinated as soon as they are eligible. This review summarizes the recent SARS-CoV-2 variants that brought challenges for vaccination and herd immunity and discusses promising management strategies.


Subject(s)
COVID-19 , SARS-CoV-2 , Humans , COVID-19/prevention & control , Immunity, Herd , COVID-19 Vaccines , Vaccination
14.
Bull Math Biol ; 84(10): 116, 2022 09 10.
Article in English | MEDLINE | ID: covidwho-2014405

ABSTRACT

COVID-19 is caused by the SARS-CoV-2 virus, which is mainly transmitted directly between humans. However, it is observed that this disease can also be transmitted through an indirect route via environmental fomites. The development of appropriate and effective vaccines has allowed us to target and anticipate herd immunity. Understanding of the transmission dynamics and the persistence of the virus on environmental fomites and their resistive role on indirect transmission of the virus is an important scientific and public health challenge because it is essential to consider all possible transmission routes and route specific transmission strength to accurately quantify the herd immunity threshold. In this paper, we present a mathematical model that considers both direct and indirect transmission modes. Our analysis focuses on establishing the disease invasion threshold, investigating its sensitivity to both transmission routes and isolate route-specific transmission rate. Using the tau-leap algorithm, we perform a stochastic model simulation to address the invasion potential of both transmission routes. Our analysis shows that direct transmission has a higher invasion potential than that of the indirect transmission. As a proof of this concept, we fitted our model with early epidemic data from several countries to uniquely estimate the reproduction numbers associated with direct and indirect transmission upon confirming the identifiability of the parameters. As the indirect transmission possess lower invasion potential than direct transmission, proper estimation and necessary steps toward mitigating it would help reduce vaccination requirement.


Subject(s)
COVID-19 , Immunity, Herd , COVID-19/prevention & control , Humans , Mathematical Concepts , Models, Biological , SARS-CoV-2
15.
Viruses ; 14(8)2022 08 22.
Article in English | MEDLINE | ID: covidwho-1997803

ABSTRACT

It has been very difficult to predict the development of the COVID-19 pandemic based on mathematical models for the spread of infectious diseases, and due to major non-pharmacological interventions (NPIs), it is still unclear to what extent the models would have fit reality in a "do nothing" scenario. To shed light on this question, the case of Sweden during the time frame from autumn 2020 to spring 2021 is particularly interesting, since the NPIs were relatively minor and only marginally updated. We found that state of the art models are significantly overestimating the spread, unless we assume that social interactions significantly decrease continuously throughout the time frame, in a way that does not correlate well with Google-mobility data nor updates to the NPIs or public holidays. This leads to the question of whether modern SEIR-type mathematical models are unsuitable for modeling the spread of SARS-CoV-2 in the human population, or whether some particular feature of SARS-CoV-2 dampened the spread. We show that, by assuming a certain level of pre-immunity to SARS-CoV-2, we obtain an almost perfect data-fit, and discuss what factors could cause pre-immunity in the mathematical models. In this scenario, a form of herd-immunity under the given restrictions was reached twice (first against the Wuhan-strain and then against the alpha-strain), and the ultimate decline in cases was due to depletion of susceptibles rather than the vaccination campaign.


Subject(s)
COVID-19 , COVID-19/epidemiology , Humans , Immunity, Herd , Pandemics/prevention & control , SARS-CoV-2 , Sweden/epidemiology
16.
Philos Trans A Math Phys Eng Sci ; 380(2233): 20210311, 2022 Oct 03.
Article in English | MEDLINE | ID: covidwho-1992466

ABSTRACT

Long-term control of SARS-CoV-2 outbreaks depends on the widespread coverage of effective vaccines. In Australia, two-dose vaccination coverage of above 90% of the adult population was achieved. However, between August 2020 and August 2021, hesitancy fluctuated dramatically. This raised the question of whether settings with low naturally derived immunity, such as Queensland where less than [Formula: see text] of the population is known to have been infected in 2020, could have achieved herd immunity against 2021's variants of concern. To address this question, we used the agent-based model Covasim. We simulated outbreak scenarios (with the Alpha, Delta and Omicron variants) and assumed ongoing interventions (testing, tracing, isolation and quarantine). We modelled vaccination using two approaches with different levels of realism. Hesitancy was modelled using Australian survey data. We found that with a vaccine effectiveness against infection of 80%, it was possible to control outbreaks of Alpha, but not Delta or Omicron. With 90% effectiveness, Delta outbreaks may have been preventable, but not Omicron outbreaks. We also estimated that a decrease in hesitancy from 20% to 14% reduced the number of infections, hospitalizations and deaths by over 30%. Overall, we demonstrate that while herd immunity may not be attainable, modest reductions in hesitancy and increases in vaccine uptake may greatly improve health outcomes. This article is part of the theme issue 'Technical challenges of modelling real-life epidemics and examples of overcoming these'.


Subject(s)
COVID-19 , Immunity, Herd , Australia/epidemiology , COVID-19/epidemiology , COVID-19/prevention & control , Humans , Queensland/epidemiology , SARS-CoV-2 , Vaccination
17.
PLoS Comput Biol ; 18(8): e1010391, 2022 08.
Article in English | MEDLINE | ID: covidwho-1987114

ABSTRACT

The COVID-19 pandemic demonstrated that the process of global vaccination against a novel virus can be a prolonged one. Social distancing measures, that are initially adopted to control the pandemic, are gradually relaxed as vaccination progresses and population immunity increases. The result is a prolonged period of high disease prevalence combined with a fitness advantage for vaccine-resistant variants, which together lead to a considerably increased probability for vaccine escape. A spatial vaccination strategy is proposed that has the potential to dramatically reduce this risk. Rather than dispersing the vaccination effort evenly throughout a country, distinct geographic regions of the country are sequentially vaccinated, quickly bringing each to effective herd immunity. Regions with high vaccination rates will then have low infection rates and vice versa. Since people primarily interact within their own region, spatial vaccination reduces the number of encounters between infected individuals (the source of mutations) and vaccinated individuals (who facilitate the spread of vaccine-resistant strains). Thus, spatial vaccination may help mitigate the global risk of vaccine-resistant variants.


Subject(s)
COVID-19 , Vaccines , COVID-19/epidemiology , COVID-19/prevention & control , Humans , Immunity, Herd , Pandemics/prevention & control , Vaccination
18.
Am J Public Health ; 112(10): 1465-1470, 2022 10.
Article in English | MEDLINE | ID: covidwho-1974455

ABSTRACT

Intermittently, the concept of herd immunity has been a potent, if sometimes ambiguous and controversial, means of framing the global response to the COVID-19 pandemic and envisaging its end. Realizing the full meaning of human herd immunity requires further attention to its connections after World War I with British social theory. Distracted by "obvious" yet unsubstantiated correspondences with veterinary research, historians of the concept have not engaged with the more proximate influence of discussions of social psychology and group dynamics on postwar epidemiology. Understanding the openness of early 20th century epidemiology to social thought deepens our appreciation of the significance of herd or population immunity, as well as suggests new avenues for exchange between public health and contemporary social sciences. (Am J Public Health. 2022;112(10):1465-1470. https://doi.org/10.2105/AJPH.2022.306931).


Subject(s)
COVID-19 , Humans , Immunity, Herd , Pandemics/prevention & control , Psychology, Social , Social Conditions , Social Sciences
19.
Animal Model Exp Med ; 5(5): 430-435, 2022 10.
Article in English | MEDLINE | ID: covidwho-1966022

ABSTRACT

The mass inoculation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines to induce herd immunity is one of the most effective measures we can deploy in the fight against coronavirus disease 2019 (COVID-19). Pregnant women are prone to a higher risk of COVID-19, and maternal infection is a risk factor for a range of neurological disorders leading to abnormal behavior in adulthood. However, there are limited clinical data to support whether vaccination or infection post-immunization in pregnant women can affect the behavioral cognition of fetuses in adulthood. In this study, human angiotensin-converting enzyme 2 pregnant mice (F0 generation) were immunized with CoronaVac and then infected with SARS-CoV-2. Subsequently, we analyzed the behavioral cognition of their adult offspring (F1 generation) using the open-field test and Morris water maze test. The adult F1 generation did not exhibit any impairments in spontaneous locomotor activity or spatial reference memory.


Subject(s)
COVID-19 , SARS-CoV-2 , Humans , Adult , Female , Mice , Pregnancy , Animals , COVID-19 Vaccines , COVID-19/prevention & control , Immunity, Herd , Vaccination
20.
Med Microbiol Immunol ; 211(4): 195-210, 2022 Aug.
Article in English | MEDLINE | ID: covidwho-1919783

ABSTRACT

In the fight against coronavirus infection, control of the immune response is of decisive importance, an important component of which is the seroprevalence of antibodies to SARS-CoV-2. Immunity to SARS-CoV-2 is formed either naturally or artificially through vaccination. The purpose of this study was to assess the seroprevalence of antibodies to SARS-CoV-2 in the population of Kyrgyzstan. A cross-sectional randomized study of seroprevalence was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The ethics committees of the Association of Preventive Medicine (Kyrgyzstan) and the St. Petersburg Pasteur Institute (Russia) approved the study. Volunteers (9471) were recruited, representing 0.15% (95% CI 0.14-0.15) of the total population, randomized by age and region. Plasma antibodies (Abs) to the nucleocapsid antigen (Nag) were determined. In vaccinated individuals, Abs to the SARS-CoV-2 receptor-binding domain antigen (RBDag) were determined. Differences were considered statistically significant at p < 0.05. The SARS-CoV-2 Nag Ab seroprevalence was 48.7% (95% CI 47.7-49.7), with a maximum in the 60-69 age group [59.2% (95% CI 56.6-61.7)] and a minimum in group 1-17 years old [32.7% (95 CI: 29.4-36.1)]. The highest proportion of seropositive individuals was in the Naryn region [53.3% (95% CI 49.8-56.8)]. The lowest share was in Osh City [38.1% (95% CI 32.6-43.9)]. The maximum SARS-CoV-2 Nag seropositivity was found in the health-care sector [57.1% (95% CI 55.4-58.8)]; the minimum was seen among artists [38.6% (95% CI 26.0-52.4)]. Asymptomatic SARS-CoV-2 Nag seropositivity was 77.1% (95% CI 75.6-78.5). Vaccination with Sputnik V or Sinopharm produced comparable Ab seroprevalence. SARS-CoV-2 Nag seropositivity in the Kyrgyz population was 48.75% (95% CI 47.7-49.7), with the mass vaccination campaign undoubtedly benefitting the overall situation.


Subject(s)
COVID-19 , Immunity, Herd , SARS-CoV-2 , Adolescent , Antibodies, Viral , COVID-19/epidemiology , Child , Child, Preschool , Cross-Sectional Studies , Humans , Infant , Kyrgyzstan/epidemiology , Seroepidemiologic Studies
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