Study population and setting
This study analyzed SARS-CoV-2 genomes from 184 samples from patients seeking COVID-19 testing in Manaus, Brazil, with the goal of understanding the second wave of disease in the region. The 184 genomes were derived from 436 PCR-confirmed or suspected SARS-CoV-2 samples collected between November 1, 2020 and January 9, 2021, and these sequences were analyzed alongside publicly available genomes from Brazil. The authors also used a larger sample of 942 samples from Brazil for which quantitative RT-PCR data were available (cycle threshold [Ct] values) to explore potential viral load differences between sequences belonging to the P.1 lineage identified in Manaus and other virus lineages. Finally, the authors used mobility data (airline data from Brazil’s Civil Aviation Agency and cell phone data from In Loco) to explore movement of the P.1 lineage, and epidemiological data such as death records (from a hospitalization database) to model the transmission dynamics of P.1 and non-P.1 virus.
Summary of Main Findings
The authors found that the second wave of COVID-19 in Manaus, Brazil was associated with the emergence and spread of a new SARS-CoV-2 lineage of concern: P.1. This lineage contains 17 amino acid changes compared to the Wuhan-Hu-1 reference genome, including 10 mutations in the spike protein, and is a descendent of lineage B.1.1.128, which was detected in Brazil in March 2020. The data presented in this study suggest the P.1 lineage emerged approximately one month prior to the resurgence of COVID-19 in Manaus, which supports the hypothesis that the second wave of disease was associated with the new variant. They also found evidence that this variant likely emerged in Manaus, and that the variant spread from Amazonas (the state in which Manaus is located) into Brazil’s southeastern states, a finding supported by both genomic and air travel data. Mathematical modeling showed that virus belonging to the P.1 lineage is likely 1.4–2.2 times more transmissible than local non-P1 lineages, though these results are not generalizable to other settings (since the authors were only able to compare to the other lineages circulating locally). To explain variations in transmissibility, the authors investigated viral Ct values over time, and found that increased transmissibility of P.1 virus could be due to higher viral loads or longer infection, though this finding was inconclusive. The authors also hypothesized that mutations in the receptor binding domain that are present in the P.1 lineage (as well as the B.1.351 lineage of concern) could improve host cell entry, but they are not able to confirm this hypothesis.
The authors performed robust phylogenetic analyses of SARS-CoV-2 genomes from Brazil, which allowed them to estimate the date and location of emergence of theP.1 variant. The availability of epidemiological and mobility data allowed them to corroborate their findings, lending additional certainty to their conclusions.
As the authors point out, their observation of increased transmission potential of the P.1 lineage is specific to the local context – without using a more global dataset, they are not able to make more general conclusions about the transmissibility of the variant. Similarly, not enough data were presented on Ct values (e.g., minimal details on where these samples were from, no lineage information available for the majority of samples, no data presented on what day of infection each sample was tested) to understand if viral loads were truly higher in virus belonging to the P.1 lineage.
This study documents the emergence of the P.1 variant of concern and describes a large outbreak associated with this new variant. It highlights the importance of tracking these variants and the need for further studies to characterize transmissibility of the variant compared to other circulating lineages, both in Brazil and worldwide.
This review was posted on: 8 April 2021