‘A study published in The Lancet analyzed the increased SARS-CoV-2 transmission in Manaus, Brazil, a region that had previously shown high levels of seroprevalence among its community members. A study conducted in October 2020 detected SARS-CoV-2 antibodies in samples from 76% of blood donors, which suggested that the region may have reached the threshold to provide some level of community immunity (ie, herd immunity). Despite the high seroprevalence, Manaus exhibited a large surge in COVID-19 cases and hospitalizations in January 2021.
‘The researchers present 4 possible explanations for the surprising surge in cases. First, the previous study could have overestimated the seroprevalence, which could have put the community below the herd immunity threshold. Second, immunity to SARS-CoV-2 conferred by earlier infection could have waned, resulting in re-infections. Third, the new infectious could be a result of emerging variants, including the P.1 variant first reported in the area, that are less susceptible to antibodies from prior infections. And finally, new SARS-CoV-2 lineages could simply be exhibiting much higher transmissibility, which could allow widespread community transmission even in areas with high existing seroprevalence. The researchers note that these theories are not mutually exclusive, and further study is needed to better characterize the factors driving the current resurgence. In particular, it is critical to investigate the potential that emerging variants could evade antibodies developed from infection with other strains, which could inform response activities in communities around the world.’
Read here (The Lancet, Jan 27, 2021)
