Eight out of ten Paulistanos had neutralizing antibodies against Covid in September

Vaccination against Covid-19 caused, in the city of São Paulo, 81.8% of the population over 18 years of age to develop neutralizing antibodies against the coronavirus in September, when 6 out of 10 adults had already received at least one dose of the immunizing agent.

This value, together with the growing advance in vaccination in the last two months, indicates a cooling of the pandemic in the city, as indicated in recent weeks by the reduction in the rates of new cases, hospitalizations and deaths.

The share of individuals who have specific antibodies against Sars-CoV-2 is 52.8%, equivalent to almost 5 million people from São Paulo. In the poorest regions of the municipality, this number reaches 62.2%, almost 9 percentage points more than in the richest regions, at 43.1%.

The results are part of the seventh stage of the serological mapping of the city carried out by the Fleury laboratory in partnership with IPEC (Intelligence in Research and Consulting, formerly Ibope), Instituto Semeia and Todos pela Saúde.

The serological study of the adult population of São Paulo uses two types of tests in order to locate specific antibodies to the coronavirus in the blood. One of them looks for IgM (produced at the beginning of the infection), IgG (from memory) and Ig (total) antibodies; the other neutralizing antibodies.

Neutralizing antibodies are able to block the entry of the virus into cells by preventing the binding of Spike S protein (used by the virus to infect cells) and are important, but not the only, protective factors against severe forms of the disease. In general, these molecules are produced after vaccination against Covid-19.

The IgG and IgM immune response against Sars-CoV-2 (also called protection against the virus nucleoprotein) is formed after a natural coronavirus infection.

It can, alternatively, occur through vaccination with Coronavac, the only one in use in the country that uses an inactivated whole virus technology, producing a defense in the body against all parts of the virus, not just the Spike protein.

There was no significant difference in the prevalence of neutralizing antibodies in the higher-income districts compared to the lower-income ones, different from what was observed in the previous steps.

“This last phase shows the importance of vaccination and how, if vaccination had started earlier, the higher prevalence of antibodies against Covid in poorer individuals compared to richer individuals would not have been observed”, says the researcher and executive director of Ipec , Márcia Cavallari Nunes. “These individuals suffered more from the disease because they were unable to stop [as atividades presenciais] and expose themselves more to the virus”, he completes.

The survey was carried out between September 9th and 20th, that is, right after the end of the application of the first dose in the entire adult population in the city. The advance of vaccination allowed including, from the sixth stage, the test of neutralizing type antibodies in the blood.

“About a third of the population already had neutralizing antibodies at the end of the sixth step, on May 1st, and two-thirds did not. Now, we see that this number rose to 81.8% by the end of this seventh step, and the The number of people in whom it was not possible to detect neutralizing antibodies dropped from 66.7% to 18.2%, which is a result of vaccination”, explains the study’s main author, biologist and professor at USP Fernando Reinach.

“We have no way of knowing what this number is today, but it is likely that it is already higher, of people with antibodies, either by vaccination or by previous infection”, he says.

The survey concludes that with about 82% of the adult population already showing neutralizing antibodies and with the current rate of vaccination, it is likely that the pandemic in the city of São Paulo will continue on a downward trajectory — provided that no new variants of the virus appear.

In this new phase, the SoroEpiSP research divided the city into 160 sectors. In each of them, eight households were randomly selected and 1,055 blood samples were collected from individuals over 18 years of age. In addition, a questionnaire was applied to these residents.

The first stage of the project, completed in May 2020, compared the neighborhoods with the highest number of cases and deaths per 100,000 inhabitants and found that 5% of the population had already come into contact with the virus.

The second stage, completed in June last year, showed a population-wide prevalence of 11.4%. In the third phase, carried out in July 2020, the observed seroprevalence was 17.9%.

In October, the fourth phase indicated that 26.2% of the adult population of São Paulo already had antibodies against the virus. The fifth stage, which took place in January of this year, indicated a third of the adult population with previous infection with the disease.

Finally, the sixth stage, carried out between April 22 and May 1, already indicated 41.6% of adults with antibodies in their blood against Sars-CoV-2. At the time, only 8.6% of the adult population in the city had received the two doses of the Covid vaccine.