The dynamics of SARS-CoV-2 variant substitution in the town where a clinical trial of vaccination effectiveness was conducted matched the pattern seen elsewhere in the country, but most cases were mild. The researchers analyzed 4,375 whole genomes of the virus.
The dynamics of SARS-CoV-2 variant substitution in the town where a clinical trial of vaccination effectiveness was conducted matched the pattern seen elsewhere in the country, but most cases were mild
A study conducted in Serrana, a small town in São Paulo state used as a model for COVID-19 vaccination in Brazil, shows that mass vaccination reduced the severe case and death rates even while the gamma and delta variants were circulating. Gamma and delta were considered alarming because they spread so much faster than previous variants.
Based on an analysis of the virus's evolutionary history (phylogeny), the researchers showed that the dynamics of SARS-CoV-2 substitution in the town was similar to the pattern seen in the rest of Brazil. The ancestral strains (B.1.1.28 and B.1.1.33) were replaced by gamma, delta (first detected in India in 2020 and originally labeled B.1.617.2) and more recently omicron. In Serrana, however, the study showed that most cases caused by all three variants (88.9%, 98.1% and 99.1% respectively) were mild, thanks to immunization with CoronaVac (Sinovac Biotech-Butantan Institute). Coverage had then reached 80% of the target population.
The phylogenetic analysis was applied to 4,375 genomes obtained between June 2020 and April 2022, the period between the introduction of SARS-CoV-2 and completion of the double-dose vaccination process.
According to the authors, their genomic surveillance exercise not only monitored the spread of the key variants in the town but also helped identify some rare variants of interest, such as C.37, which circulated in the Andean countries but was under-represented in Brazil, and alpha, which was detected in Serrana but did not spread elsewhere. All told, the scientists detected 52 sublineages of SARS-CoV-2 in the town.
An article on the study is published in the journal Viruses. Codenamed Project S, the study was conducted by Butantan Institute with FAPESP's support. The authors are researchers…