Brazil's COVID-19 Epicenter in Manaus: How Much of the Population Has Already Been Exposed and Are Vulnerable to SARS-CoV-2?

Abstract

Is Brazil's COVID-19 epicenter really approaching herd immunity? A recent study estimated that in October 2020 three-quarters of the population of Manaus (the capital of the largest state in the Brazilian Amazon) had contact with SARS-CoV-2. We show that 46% of the Manaus population having had contact with SARS-CoV-2 at that time is a more plausible estimate, and that Amazonia is still far from herd immunity. The second wave of COVID-19 is now evident in Manaus. We predict that the pandemic of COVID-19 will continue throughout 2021, given the duration of naturally acquired immunity of only 240 days and the slow pace of vaccination. Manaus has a large percentage of the population that is susceptible (35 to 45% as of May 17, 2021). Against this backdrop, measures to restrict urban mobility and social isolation are still necessary, such as the closure of schools and universities, since the resumption of these activities in 2020 due to the low attack rates of SARS-CoV-2 was the main trigger for the second wave in Manaus.

Keywords: Amazon; Coronavirus; Herd immunity; Immunity loss; Manaus; Reinfection; SEIR; SEIRS.

Fig. 1

Simulation of COVID-19 in Manaus using A the infection fatality ratio (IFR) value from Buss et al. [3] and B a more realistic IFR value. Infected individuals are shown by the black curve, while hospitalized patients are scaled to fit the black curve (daily counts in orange and moving window of averaged daily counts in red). Blue shading indicates 95% and 68% confidence intervals. The more realistic scenario in B indicates substantial continued infections (and consequently deaths)

Fig. 2

Model with best fit and that best explains the first and second COVID-19 waves in Manaus. In A, violet (dark green) indicates the projected (observed) deaths. In B, orange indicates daily observed hospitalizations; the projected hospitalizations due to the two SARS-CoV-2 variants are indicated in green (original), blue (gamma variant or P.1), and black (total). C shows the community use of public transport (busses), compared to the February 2020 baseline