COVID-19 herd immunity in the Brazilian Amazon

Abstract

The herd immunity threshold is the proportion of a population that must be immune to an infectious disease, either by natural infection or vaccination such that, in the absence of additional preventative measures, new cases decline and the effective reproduction number falls below unity. This fundamental epidemiological parameter is still unknown for the recently-emerged COVID-19, and mathematical models have predicted very divergent results. Population studies using antibody testing to infer total cumulative infections can provide empirical evidence of the level of population immunity in severely affected areas. Here we show that the transmission of SARS-CoV-2 in Manaus, located in the Brazilian Amazon, increased quickly during March and April and declined more slowly from May to September. In June, one month following the epidemic peak, 44% of the population was seropositive for SARS-CoV-2, equating to a cumulative incidence of 52%, after correcting for the false-negative rate of the antibody test. The seroprevalence fell in July and August due to antibody waning. After correcting for this, we estimate a final epidemic size of 66%. Although non-pharmaceutical interventions, plus a change in population behavior, may have helped to limit SARS-CoV-2 transmission in Manaus, the unusually high infection rate suggests that herd immunity played a significant role in determining the size of the epidemic.

Inference of COVID-19 epidemiological distributions from Brazilian hospital data

“…Ninety-five per cent credible intervals are given in brackets for mean and variance. The parameters p 1 , p 2 and p 3 for the preferred PDFs gamma and generalized lognormal (GLN) are given in the form gamma(x|p 1 , p 2 ) = gamma(α, β) and GLN(x|p 1 , p 2 , p 3 ) = GLN(μ, σ, s), with the formulae of the PDFs given in appendix B, Across Brazil, the epidemic has strong geographical heterogeneity, with some states such as Amazonas and Maranhão reported to be at advanced stages [40,41]. To describe the observed differences at subnational level accurately, using a mathematical model, it is essential to account for variation in model parameters by state.…”

Clinical features and natural history of the first 2073 suspected COVID-19 cases in the Corona São Caetano primary care programme: a prospective cohort study

“…10 The reasons for the exceptionally large epidemic in Brazil have been discussed elsewhere. 11–13 In March 2020, the Municipal Health Department of the municipality of São Caetano do Sul—part of the Greater Metropolitan Region of São Paulo—began to develop a clinical and testing platform to organise its COVID-19 response. The aim was to provide universal detection and management of symptomatic cases and their contacts.…”

Changing Research Paradigm in the Face of a Global Pandemic: Foreseeable Impact and Adaptive Measures in Academic Research in the Future

“…This pool can then be extrapolated to form and prove various hypotheses. Thus, the methodology of research will shift towards compilation of evidence from square tone, gradually building onto original cohort studies and laboratory-based research [7,22]. Since, majority of the study methodologies do not support long distance participation, the use of surveys will become more popular.…”

“…The objective of this paper is to identify the areas of research that may be aff ected in the pandemic period and to predict possible solutions for ethical, valid and useful research [7].…”