Thursday, January 28, 2021

The Lancet: Resurgence of COVID-19 in Manaus, Brazil, Despite High Seroprevalence


We've been following the impact of a new wave of COVID this winter in Amazonas State, Brazil (see Brazil: Amazonas Transfers 235 COVID Cases To Other States Amid Critical Oxygen Shortage), and the rise of new COVID Variants in the region for several weeks. 

Making this outbreak even more remarkable are recent studies that suggest the population of Manaus, the capital and largest city in Amazonas, already had a high seroprevalence level of COVID following a heavy wave of the virus last spring (see Three-quarters attack rate of SARS-CoV-2 in the Brazilian Amazon during a largely unmitigated epidemic. Science. 2020; 371: 288-292).
With 76% of the population estimated to have already been infected with SARS-CoV-2 - enough to presumably supply some degree of `herd immunity' - another large outbreak raises serious questions about durability of acquired immunity, and/or antigenic changes to the virus in the region. 
All of which brings us to a relatively brief comment, published yesterday in The Lancet, that proposes 4 non-exclusive possibilities behind this resurgence. 
  1. The SARS-CoV-2 attack rate could have been overestimated during the first wave, leaving the population below the herd immunity threshold until the beginning of this latest wave. 
  2. Acquired immunity against SARS-CoV-2 may already have begun to wane in the community as it is now 7 to 8 months after the first wave.
  3. Brazil has reported both the UK B.1.1.7 and the indigenous P.1. variant (and more recently a P.2 variant), some of which may evade immunity acquired from previous variants of the virus.
  4. These new variants may have a higher transmissibility than previous variants.
Whether driven by declining immunity in the general population, or increased transmissibility or antigenic escape by new variants (or a combination of both), the concern is that other regions may be faced wotj similar resurgences in the coming months. 

The following article discusses the pros and cons of each of these possibilities and the importance of determining the efficacy of existing COVID-19 vaccines against these new variants.