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1.
Philos Trans A Math Phys Eng Sci ; 380(2233): 20210311, 2022 Oct 03.
Artigo em Inglês | MEDLINE | ID: covidwho-1992466

RESUMO

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'.


Assuntos
COVID-19 , Imunidade Coletiva , Austrália/epidemiologia , COVID-19/epidemiologia , COVID-19/prevenção & controle , Humanos , Queensland/epidemiologia , SARS-CoV-2 , Vacinação
2.
Med Microbiol Immunol ; 211(4): 195-210, 2022 Aug.
Artigo em Inglês | MEDLINE | ID: covidwho-1919783

RESUMO

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.


Assuntos
COVID-19 , Imunidade Coletiva , SARS-CoV-2 , Adolescente , Anticorpos Antivirais , COVID-19/epidemiologia , Criança , Pré-Escolar , Estudos Transversais , Humanos , Lactente , Quirguistão/epidemiologia , Estudos Soroepidemiológicos
3.
J Math Biol ; 85(1): 2, 2022 Jun 30.
Artigo em Inglês | MEDLINE | ID: covidwho-1906031

RESUMO

We study a susceptible-exposed-infected-recovered (SEIR) model considered by Aguas et al. (In: Herd immunity thresholds for SARS-CoV-2 estimated from unfolding epidemics, 2021), Gomes et al. (In: J Theor Biol. 540:111063, 2022) where individuals are assumed to differ in their susceptibility or exposure to infection. Under this heterogeneity assumption, epidemic growth is effectively suppressed when the percentage of the population having acquired immunity surpasses a critical level - the herd immunity threshold - that is lower than in homogeneous populations. We derive explicit formulas to calculate herd immunity thresholds and stable configurations, especially when susceptibility or exposure are gamma distributed, and explore extensions of the model.


Assuntos
COVID-19 , Epidemias , COVID-19/epidemiologia , Humanos , Imunidade Coletiva , Reinfecção/epidemiologia , SARS-CoV-2
4.
Arch Virol ; 167(9): 1773-1783, 2022 Sep.
Artigo em Inglês | MEDLINE | ID: covidwho-1899184

RESUMO

Currently, health authorities around the world are struggling to limit the spread of COVID-19. Since the beginning of the pandemic, social distancing has been the most important strategy used by most countries to control disease spread by flattening and elongating the epidemic curve. Another strategy, herd immunity, was also applied by some countries through relaxed control measures that allow the free spread of natural infection to build up solid immunity within the population. In 2021, COVID-19 vaccination was introduced with tremendous effort as a promising strategy for limiting the spread of disease. Therefore, in this review, we present the current knowledge about social distancing, herd immunity strategies, and aspects of their implementation to control the COVID-19 pandemic in the presence of the newly developed vaccines. Finally, we suggest a short-term option for controlling the pandemic during vaccine application.


Assuntos
COVID-19 , COVID-19/prevenção & controle , Vacinas contra COVID-19 , Humanos , Imunidade Coletiva , Pandemias/prevenção & controle , Distanciamento Físico , SARS-CoV-2
6.
J R Soc Med ; 115(6): 239-240, 2022 06.
Artigo em Inglês | MEDLINE | ID: covidwho-1865224
7.
Epidemics ; 39: 100581, 2022 06.
Artigo em Inglês | MEDLINE | ID: covidwho-1851044

RESUMO

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.


Assuntos
COVID-19 , Imunidade Coletiva , Adulto , COVID-19/epidemiologia , COVID-19/prevenção & controle , Vacinas contra COVID-19 , Criança , Humanos , Pessoa de Meia-Idade , Estudos Soroepidemiológicos , Vacinação/métodos , Cobertura Vacinal
8.
PLoS One ; 17(5): e0267840, 2022.
Artigo em Inglês | MEDLINE | ID: covidwho-1843583

RESUMO

We introduce a novel compartmental model accounting for the effects of vaccine efficacy, deployment rates and timing of initiation of deployment. We simulate different scenarios and initial conditions, and we find that higher abundancy and rate of deployment of low efficacy vaccines lowers the cumulative number of deaths in comparison to slower deployment of high efficacy vaccines. We also forecast that, at the same daily deployment rate, the earlier introduction of vaccination schemes with lower efficacy would also lower the number of deaths with respect to a delayed introduction of high efficacy vaccines, which can however, still achieve lower numbers of infections and better herd immunity.


Assuntos
Vacinação , Vacinas , Imunidade Coletiva
9.
Internist (Berl) ; 63(5): 476-483, 2022 May.
Artigo em Alemão | MEDLINE | ID: covidwho-1772882

RESUMO

Due to the effectiveness of vaccines some particularly threatening infectious diseases have become rare; however, vaccines are meanwhile the victims of their own success. Due to insufficient compliance and inadequate vaccination rates, there is a danger that the effectiveness of vaccination as a preventive measure will continuously disappear. In 2019 the World Health Organization classified doubts on the effectiveness of vaccines as 1 of the 10 greatest dangers to health worldwide. This article discusses important questions on vaccinations and vaccines as well as their effects in the interplay with the immune system. The following topics are covered: comparison of naturally acquired immunity and that acquired by vaccination, factors that necessitate a refresher vaccination, the role of herd immunity, prerequisites for successful eradication of a disease, influence of various T cells on the effect of vaccination, the role of immunologic memory, factors that influence protection by vaccination, vaccinations in cases of immunodeficiency, the potential and areas of implementation of passive immunization. In view of the corona pandemic and the running vaccination campaign, it must be hoped that this triggers a general renaissance of vaccinations against infectious diseases.


Assuntos
Memória Imunológica , Vacinas , Humanos , Imunidade Coletiva , Programas de Imunização , Vacinação
10.
Nat Rev Immunol ; 22(6): 333-334, 2022 06.
Artigo em Inglês | MEDLINE | ID: covidwho-1799586
11.
Recent Pat Biotechnol ; 16(3): 256-265, 2022 Aug 03.
Artigo em Inglês | MEDLINE | ID: covidwho-1785254

RESUMO

The severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has spread exponentially, leading to an alarming number of deaths worldwide. A devastating effect has been observed in susceptible populations. Our body's immune system plays a very important role in fighting against diseases. The principle of herd immunity (also known as population immunity), which has found its way into science and has been in the limelight, is the most widely recognised among all. It is an indirect defence against infectious diseases when a community gained immunity, either through vaccines or through prior infection. Herd immunity against COVID-19 must be achieved to reduce the transmission of disease and save lives. Therefore, this review provides a comprehension of the role of immunity, with a special emphasis on herd immunity against COVID-19, and the ways to attain herd immunity in India have also been discussed.


Assuntos
COVID-19 , Imunidade Coletiva , COVID-19/prevenção & controle , Humanos , Índia/epidemiologia , Patentes como Assunto , SARS-CoV-2
12.
Soc Sci Med ; 298: 114800, 2022 04.
Artigo em Inglês | MEDLINE | ID: covidwho-1747569

RESUMO

Despite unprecedented progress in developing COVID-19 vaccines, global vaccination levels needed to reach herd immunity remain a distant target, while new variants keep emerging. Obtaining near universal vaccine uptake relies on understanding and addressing vaccine resistance. Simple questions about vaccine acceptance however ignore that the vaccines being offered vary across countries and even population subgroups, and differ in terms of efficacy and side effects. By using advanced discrete choice models estimated on stated choice data collected in 18 countries/territories across six continents, we show a substantial influence of vaccine characteristics. Uptake increases if more efficacious vaccines (95% vs 60%) are offered (mean across study areas = 3.9%, range of 0.6%-8.1%) or if vaccines offer at least 12 months of protection (mean across study areas = 2.4%, range of 0.2%-5.8%), while an increase in severe side effects (from 0.001% to 0.01%) leads to reduced uptake (mean = -1.3%, range of -0.2% to -3.9%). Additionally, a large share of individuals (mean = 55.2%, range of 28%-75.8%) would delay vaccination by 3 months to obtain a more efficacious (95% vs 60%) vaccine, where this increases further if the low efficacy vaccine has a higher risk (0.01% instead of 0.001%) of severe side effects (mean = 65.9%, range of 41.4%-86.5%). Our work highlights that careful consideration of which vaccines to offer can be beneficial. In support of this, we provide an interactive tool to predict uptake in a country as a function of the vaccines being deployed, and also depending on the levels of infectiousness and severity of circulating variants of COVID-19.


Assuntos
COVID-19 , Vacinas , COVID-19/prevenção & controle , Vacinas contra COVID-19/uso terapêutico , Humanos , Imunidade Coletiva , Vacinação
13.
Science ; 375(6585): 1088-1089, 2022 03 11.
Artigo em Inglês | MEDLINE | ID: covidwho-1736007

RESUMO

How much do COVID-19 vaccines reduce transmission? The answer is a moving target.


Assuntos
COVID-19 , Imunidade Coletiva , COVID-19/prevenção & controle , Vacinas contra COVID-19 , Humanos , Imunidade Coletiva/imunologia , SARS-CoV-2 , Vacinação/veterinária
14.
J R Soc Interface ; 19(188): 20210896, 2022 03.
Artigo em Inglês | MEDLINE | ID: covidwho-1735716

RESUMO

An age-structured SEIR model simulates the propagation of COVID-19 in the population of Northern Ireland. It is used to identify optimal timings of short-term lockdowns that enable long-term pandemic exit strategies by clearing the threshold for herd immunity or achieving time for vaccine development with minimal excess deaths.


Assuntos
COVID-19 , COVID-19/epidemiologia , COVID-19/prevenção & controle , Controle de Doenças Transmissíveis , Humanos , Imunidade Coletiva , Irlanda do Norte/epidemiologia , SARS-CoV-2
15.
PLoS One ; 17(2): e0253638, 2022.
Artigo em Inglês | MEDLINE | ID: covidwho-1910476

RESUMO

Population immunity (herd immunity) to SARS-CoV-2 derives from two sources: vaccinations or cases of infection with the virus. Infections can be diagnosed as COVID-19 and registered, or they can be asymptomatic, oligosymptomatic, or even full-blown but undiagnosed and unregistered when patients recovered at home. Estimation of population immunity to SARS-CoV-2 is difficult and remains a subject of speculations. Here we present a population screening for SARS-CoV-2 specific IgG and IgA antibodies in Polish citizens (N = 501) who had never been positively diagnosed with or vaccinated against SARS-CoV-2. Serum samples were collected in Wroclaw (Lower Silesia) on 15th and 22nd May 2021. Sera from hospitalized COVID-19 patients (N = 22) or from vaccinated citizens (N = 14) served as positive controls. Sera were tested with Microblot-Array COVID-19 IgG and IgA (quantitative) that contain specific SARS-CoV-2 antigens: NCP, RBD, Spike S2, E, ACE2, PLPro protein, and antigens for exclusion cross-reactivity with other coronaviruses: MERS-CoV, SARS-CoV, HCoV 229E Np, HCoV NL63 Np. Within the investigated population of healthy individuals who had never been positively diagnosed with or vaccinated against SARS-CoV-2, we found that 35.5% (178 out of 501) were positive for SARS-CoV-2-specific IgG and 52.3% (262 out of 501) were positive for SARS-CoV-2-specific IgA; 21.2% of the investigated population developed virus-specific IgG or IgA while being asymptomatic. Anti-RBD IgG, which represents virus-neutralizing potential, was found in 25.6% of individuals (128 out of 501). These patients, though positive for anti-SARS-CoV-2 antibodies, cannot be identified in the public health system as convalescents due to undiagnosed infections, and they are considered unaffected by SARS-CoV-2. Their contribution to population immunity against COVID-19 should however be considered in predictions and modeling of the COVID-19 pandemic. Of note, the majority of the investigated population still lacked anti-RBD IgG protection (74.4%); thus vaccination against COVID-19 is still of the most importance for controlling the pandemic.


Assuntos
Infecções Assintomáticas/epidemiologia , Vacinas contra COVID-19/uso terapêutico , COVID-19/epidemiologia , COVID-19/imunologia , Imunidade Coletiva , Pandemias/prevenção & controle , SARS-CoV-2/imunologia , Vacinação/métodos , Adolescente , Adulto , Idoso , Anticorpos Antivirais/sangue , Anticorpos Antivirais/imunologia , Antígenos Virais/imunologia , COVID-19/sangue , COVID-19/prevenção & controle , Reações Cruzadas , Feminino , Humanos , Imunoglobulina A/sangue , Imunoglobulina A/imunologia , Imunoglobulina G/sangue , Imunoglobulina G/imunologia , Masculino , Pessoa de Meia-Idade , Polônia/epidemiologia , Resultado do Tratamento , Adulto Jovem
16.
J Theor Biol ; 540: 111063, 2022 05 07.
Artigo em Inglês | MEDLINE | ID: covidwho-1693204

RESUMO

Individual variation in susceptibility and exposure is subject to selection by natural infection, accelerating the acquisition of immunity, and reducing herd immunity thresholds and epidemic final sizes. This is a manifestation of a wider population phenomenon known as "frailty variation". Despite theoretical understanding, public health policies continue to be guided by mathematical models that leave out considerable variation and as a result inflate projected disease burdens and overestimate the impact of interventions. Here we focus on trajectories of the coronavirus disease (COVID-19) pandemic in England and Scotland until November 2021. We fit models to series of daily deaths and infer relevant epidemiological parameters, including coefficients of variation and effects of non-pharmaceutical interventions which we find in agreement with independent empirical estimates based on contact surveys. Our estimates are robust to whether the analysed data series encompass one or two pandemic waves and enable projections compatible with subsequent dynamics. We conclude that vaccination programmes may have contributed modestly to the acquisition of herd immunity in populations with high levels of pre-existing naturally acquired immunity, while being crucial to protect vulnerable individuals from severe outcomes as the virus becomes endemic.


Assuntos
COVID-19 , SARS-CoV-2 , COVID-19/epidemiologia , COVID-19/prevenção & controle , Humanos , Imunidade Coletiva , Pandemias/prevenção & controle , Vacinação
17.
Sci Rep ; 12(1): 2640, 2022 02 16.
Artigo em Inglês | MEDLINE | ID: covidwho-1692543

RESUMO

Currently, several western countries have more than half of their population fully vaccinated against COVID-19. At the same time, some of them are experiencing a fourth or even a fifth wave of cases, most of them concentrated in sectors of the populations whose vaccination coverage is lower than the average. So, the initial scenario of vaccine prioritization has given way to a new one where achieving herd immunity is the primary concern. Using an age-structured vaccination model with waning immunity, we show that, under a limited supply of vaccines, a vaccination strategy based on minimizing the basic reproduction number allows for the deployment of a number of vaccine doses lower than the one required for maximizing the vaccination coverage. Such minimization is achieved by giving greater protection to those age groups that, for a given social contact pattern, have smaller fractions of susceptible individuals at the endemic equilibrium without vaccination, that is, to those groups that are more vulnerable to infection.


Assuntos
COVID-19/epidemiologia , Imunidade Coletiva , Modelos Imunológicos , SARS-CoV-2/imunologia , Vacinação , Adulto , Fatores Etários , Idoso , COVID-19/imunologia , COVID-19/prevenção & controle , COVID-19/transmissão , Criança , Humanos
18.
J Correct Health Care ; 28(2): 71-74, 2022 04.
Artigo em Inglês | MEDLINE | ID: covidwho-1692285

RESUMO

Controlling the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been challenging in the community and prison systems. Where herd immunity lies for this virus is unknown, although estimates have ranged from 60% to 80%. Since the start of the pandemic, there have been multiple SARS-CoV-2 outbreaks within U.S. prison systems, which may provide more insight on where true herd immunity lies. We reviewed data from the California Department of Corrections and Rehabilitation to investigate the cumulative incidence of infection and found levels in 14 (40%) of 35 prisons were >60%. These data and existing literature suggest that in prison environments, prevalence of immunity often needs to reach >70% before transmission slows. Similar levels may be needed in the general population before transmission is suppressed.


Assuntos
COVID-19 , Prisioneiros , COVID-19/epidemiologia , Humanos , Imunidade Coletiva , Incidência , SARS-CoV-2
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