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Two days after researchers from Imperial College London announced that antibody levels against Covid-19 fall three months after infection with the new coronavirus, new research, published in the prestigious journal Science, shows that the immune response continues being solid for at least at least five months.
The Imperial College article is still in prepress, meaning it has not been peer reviewed. The Science study, on the other hand, underwent rigorous evaluation by other scientists in the field.
The new study, published Wednesday afternoon (28), analyzed data from 30,082 people who had been examined at the Mount Sinai Health Complex in New York, United States.
According to the researchers, most of the patients who had mild or moderate Covid-19 maintain detectable levels of antibodies and the values found remain stable months after infection.
The authors specifically looked at IgG antibodies (immunoglobulin G, associated with the defense of memory and that appears later, with the patient recovered), observing the immune response in relation to the peak protein (the structure that the virus uses to bind to human cells). .
The method used for the detection of antibodies had a high sensitivity, greater than 90%, and a specificity of 100%.
With data from more than 30,000 people available, the researchers found that the majority of those infected with Covid-19 developed moderate or high levels of antibodies. The same had already been pointed out by previous investigations.
As not all patients had confirmation of the new coronavirus by PCR tests (considered the gold standard for detecting the disease), the researchers performed a second and third analysis with 568 people with PCR confirmation of the virus and 2,347 people who they were declared PCR. positive for the new coronavirus.
The results showed that more than 99% and 95% of these subgroups, respectively, had antibodies against Covid-19.
“Therefore, the proportion of people who do not have seroconversion [produção de anticorpos] it is low, although these individuals exist, ”say the authors.
Finally, the researchers followed 121 patients to check their antibody levels over time. These people had undergone serological tests approximately 30 days after the onset of symptoms. The second and third antibody level checks were performed, respectively, approximately 82 and 148 days after the onset of symptoms.
Antibody levels, according to the scientists, remain stable for at least three months, with modest declines after five months.
“Our data reveals that people who recovered from mild Covid-19 images have a relatively robust antibody response to the spike protein, which is significantly correlated with neutralization of Sars-CoV-2,” say the authors. The plan now is to continue monitoring these patients.
The research does not conclusively indicate that the antibodies found protect against reinfection, but the authors say they believe it is “very likely that they reduce the chances of reinfection and may alleviate the disease in cases of infection.”
Contested by experts, the Imperial College London study examined 17,576 people with IgG antibodies detected by rapid tests (less accurate than the method used in the study published in Science). Comparing the three phases of the investigation, there was a drop in the antibody rate of 26.5%.
The authors even claimed that this drop could be related to the rise in new coronavirus cases in the UK from September.
The study, however, had several limitations in addition to the precision of the test used. The first, reported by the authors themselves, consists of the study design: random and non-overlapping population samples were selected, that is, there was no follow-up of the drop in antibodies in identical populations between the three phases. The authors also state that the importance of antibodies both for protection and for the possibility of reinfection is not very clear.
Also, it is normal for the level of antibodies to drop after a person’s body has overcome an infection. Still, the cells of the immune system carry a memory of viruses and can produce new antibodies when needed.
Data from monkey studies suggest that even low levels of antibodies can prevent severe cases of disease, even if they do not prevent reinfection.
Some people may not make antibodies, but even these people may have immune cells called T cells, which can identify and destroy the virus. Most people infected with the coronavirus develop lasting cellular responses, according to recent studies.
According to Raquel Stucchi, a researcher at Unicamp and a consultant for the SBI (Brazilian Society of Infectious Diseases), the difference in methodologies does not allow a direct comparison between the Mount Sinai study and the Imperial College study. It points out, however, the need for more studies investigating the antibodies against different antigens of the virus and the role of each in the evolution of the disease and in subsequent protection.
The divergence in studies shows that we still know little about the duration of protection against possible reinfection and about antibodies against Covid-19.
For this reason, Stuchhi points out that it is important that even those who have had the disease maintain protective measures, such as the use of a mask, social distance and hand hygiene.
“We still don’t have enough knowledge to say that the disease provides protection later or not. The practical importance of the new study is not yet known, but it is encouraging.
With the New York Times
