A study carried out by University of São Paulo (USP) in partnership with Oxford University, in England, found that about a third of the Covid-19 cases detected in Manaus since January were reinfections by the variant P.1.
According to the article, in October 2020, 76% of residents had already been exposed to SARS-CoV-2, which is the Covid-19 virus. In the second wave faced by the capital of Amazonas, 87% of the cases would have been caused by the P.1 variant.
The work was led by researchers Ester Sabino, from USP, and Nuno Faria, from Oxford University. In all, blood samples were analyzed from 238 blood donors that met specific criteria, such as having made three or more donations, at least one of them before July 2020 and a second between January and March 2021.
In the article, which has yet to be peer-reviewed, the group describes how antibodies and immune system molecules reacted to antibody tests on each of the samples. After that, they determined which of the volunteers could have been more than once based on the strength of the immune response presented by them.
"Our data suggest that reinfection by P.1 is more common and more frequent than had been detected by traditional methods of genomic, molecular and epidemiological surveillance of clinical cases," say the scientists in the study.
Previous study received criticism
However, this high estimate of the prevalence of Covid-19 as measured by the group has attracted some criticism from scientists in Manaus. The main one is that this proportion of infected (87%), would represent that Manaus has achieved group immunity against Covid-19.
These figures were even used by politicians and traders in the region as an argument to call for the reopening of trade. Flexibilization was carried out and ended up resulting in a outbreak of the disease in the city, when the health system collapsed and even oxygen was lacking for patients.
It was in this context that the P.1 variant expanded its circulation, but, for some epidemiologists, this was not the only reason for the dimension of the second wave. In addition, for them, blood donors are not a population that provides a reliable diagnosis of the spread of the disease.
“Donors have an age group that does not represent the whole of Manaus, excluding children and the elderly. And, in addition, those who donate blood in general are from the middle or lower class, and this also restricts the population analyzed ”, said the epidemiologist at Fiocruz Manaus, Marcus Lacerda, newspaper The Globe.
Another point of attention is the fact that people who have not yet had antibodies against Covid-19 as positive diagnoses. “The test had a determined sensitivity, and they ended up reducing it. This resulted in a positive group of people who probably did not have IgG, that is, did not have an antibody against Covid-19 ”, says Lacerda.
USP / Oxford team responses
The first study led by Sabino and Faria on the topic was published in the journal Science in 2020 and received some criticism from peers, which have been answered since then. Ester Sabino says that due care was taken to avoid distortions in the study results.
“We discounted the false positive rate. We did, yes, several tests using several different cuts manufacturers. They all hit the same value. We made other models to correct the drop in antibodies and hit the same estimate, ”she said.
On the issue of collective immunity, Sabino says that the study was misinterpreted outside the scientific community, in addition to that he never said that the epidemic was controlled in Manaus. “Communicating science is very difficult. In fact, our work came out as an “attack rate”, and not as “herd immunity” “, said the researcher.
“I could have changed the title. At the time, I didn't think people would understand it by looking at the title that way. But I don't think what we did is wrong. This is not saying that the epidemic is over at any time, and it is very clear in our text ”, he reinforces.
"I think it would be very wrong if I did not tell the population that we had found such a high prevalence in Manaus, because now it gives the context to know that they can catch Covid-19 a third time too," she concluded.