The vast majority of people contaminated with the original strain of coronavirus have antibodies that can also neutralize the P.1 variant, which appeared in the city of Manaus (AM) in November 2020 and is believed to be more easily transmissible. The discovery was made through laboratory tests at the Institute of Tropical Medicine at the University of São Paulo (IMT-USP).
The experiments were carried out on blood plasma collected between May and June last year from 60 volunteers infected with the B.1.1.28 strain of SARS-CoV-2, the first strain identified in the country. In 84% of the cases, antibodies in samples taken after the 15th day of infection were able to neutralize P.1 in cell cultures.
The full data of the FAPESP-funded study have been published on the medRxiv platform and are still in the peer review process.
“The results suggest that people infected with the ancestral strain of SARS-CoV-2 tend to be better protected when they encounter the new variant. This does not exclude the risk of reinfection, symptomatic illness, or even death. In any case, it is a message of hope at a time when things are very complicated, ”says Maria Cassia Mendes-Correa, professor at the Faculty of Medicine (FM-USP) and lead author of the article.
The research was carried out as part of the Corona-São-Caetano program, an online platform created to organize remote monitoring by health teams of residents with symptoms of COVID-19 and the collection of samples for diagnosis at home. The Municipal University of São Caetano do Sul (USCS), the local town hall, the startup MRS – Modular Research System and the IMT-USP are participating in the initiative
After the diagnosis was confirmed by an RT-PCR test, the 60 volunteers with mild symptoms who entered the study were monitored for 42 days and had weekly blood draws for analysis of the serological profile. Each plasma sample was subjected to a virus neutralization assay (VNT), a procedure that involves the cultivation of SARS-CoV-2 in vitro and therefore requires a laboratory structure with high biosafety.
In contrast to conventional laboratory tests, which detect the presence of IgM antibodies (immunoglobulin M, which is formed first in the acute phase) and IgG (immunoglobulin G, which appears at the end of the acute phase), the VNT technique allows the amount of Measured in plasma by neutralizing antibodies – which can bind to the tip of the spike protein used by SARS-CoV-2 to connect to the human cell receptor and facilitate infection. This region of the protein is known as the RBD (acronym for receptor binding domain).
The P.1 variant has been a cause for concern as it has mutations in the spike protein – some of them in the RBD region.
“The neutralizing antibody is one of the body’s most important antiviral tools. Its production is gradual until it reaches enough to kill the infection. In most patients, the curve rises in the first two weeks and then remains stable, ”says the researcher.
In tests carried out with strain B.1.1.28, the antibodies contained in the plasma of 56 volunteers (90%) were able to neutralize the virus in culture. In P.1, samples from 50 participants (84%) were successful in the test. In both cases, sufficient neutralizing antibodies were not present to fight the virus until day 15 of infection, and the performance against the ancestral strain was superior at any point in time.
“It is important to emphasize that the tests were carried out on plasma collected in 2020 and therefore it cannot be said that these people would be equally protected today. Neutralizing antibodies and those of the IgG and IgM types tend to decay over time, ”explains the researcher.
To dispel this doubt, the IMT-USP group repeated the tests with plasma samples taken from the same volunteers 180 days after infection. The results of this second research phase are to be published shortly.
In addition, in 2020 the researchers will test collected plasma for other variants of concern such as B.1.1.7 (discovered in the UK) and B.1.351 (from South Africa).
Although neutralizing antibodies are one of the immune system’s most important tools to fight the virus, neutralizing antibodies aren’t the only ones, says Mendes-Correa. “Cellular immunity mediated by lymphocytes [células capazes de reconhecer e destruir o patógeno], is another mechanism to ward off SARS-CoV-2 and also an important tool in this process. We believe that the combination of these two mechanisms leads to our ability to get rid of pathogens. “
* With information from Portal R7