First exposure to the coronavirus may not produce immune memory

In its efforts against the pandemic, Fiocruz researchers have observed that memory for the immune response against the coronavirus, which would prevent reinfection, may not occur in mild cases. The discovery took place after sequencing the genotypes of the new coronavirus, and reinforces the fact that reinfection by the Sars-CoV-2 is possible. Viral Genetic Evidence and Host Immune Response of a Small Cluster of Individuals with Two Episodes of Sars-Cov-2 Infection, the paper currently in pre-print at Social Science Research Network (SSRN), was coordinated by Thiago Moreno, researcher of the Center of Technological Development in Health (CDTS/Fiocruz).

The research followed up four asymptomatic individuals on a weekly basis starting at the beginning of the pandemic, in March. The subjects followed in the research were submitted to serology and RT-PCR tests during the process. While sequencing the genomes, researchers confirmed that one person was infected by the virus associated with a genome imported into the country, while another showed a viral structure associated with the genome already circulating in Rio de Janeiro. All individuals tested positive for Covid-19 but had no symptoms at all.

According to Thiago Moreno, one of the people followed by the study sought the research group again in late May reporting more intense signs and symptoms of Covid-19, such as fever and loss of senses of smell and taste. “When we ran the RT-PCR test again, all four tested positive. What we observed was reinfection within the family environment. However, the person who had, in March, the genotype associated with cases imported into Brazil was now infected by another strain. After sequencing, it was also observed that another subject who had been infected with the genotype circulating in Rio still had the same genotype, but with accumulated mutations that allowed for the interpretation that this was reinfection and not a persistent infection”, he explains.

For the virologist, the study strengthened the notion that reinfection by the new coronavirus is possible and that this is common among coronaviruses, emphasizing that the first exposure to the virus does not result in immune memory. “Asymptomatic or very mild cases, when re-exposed to the virus, may present infection again. This time, the disease may be more serious and the new infection may be more severe than the first, such as demonstrated by the paper. This is why the population should be warned about immunity against the coronavirus. In some cases, the immune response may be intense early on, but this does not mean they are long-lasting”, he concludes.