Covid-19 reinfection: mild disease can give ‘false security’ without guaranteeing immunity, warns Fiocruz scientist

In two of these cases, the researchers confirmed by genetic testing of virus samples collected on both occasions that they were two different variants of Sars-CoV-2.

In the other two, there were no samples of the first infection, but scientists say it is difficult not to treat reinfection cases based on clinical and epidemiological criteria.

The scientists then investigated why the four patients were re-infected with the coronavirus and, from an antibody analysis, concluded that their bodies did not create an immune memory after the first infection.

As a result, they remained vulnerable to the coronavirus and ended up getting contaminated again.

“This is a warning sign for people who may have a false perception of security after having a mild covid-19 in the first wave or at the beginning of this second wave that we are seeing in Brazil and in the world,” says Moreno to BBC News Brazil. .

The research was published on the Social Science Research Network and has not yet been reviewed by other scientists.

There is still insufficient data globally to understand the frequency of reinfections.

According to the Ministry of Health, until last Monday (12/21), there were 58 suspected cases in Brazil under analysis.

One difficulty in confirming these cases is having samples from the same patient in both infections to be able to do the genetic sequencing of the viruses on each occasion to certify that they are different strains.

This proves that it is not a persistent infection, in which the same virus has multiplied after a while. But without this, it is more difficult to prove reinfection, and this was a problem that Moreno faced in his research.

Reinfection could be verified in two of the cases, the middle-aged woman and her son-in-law, because genetic tests showed that they were different strains.

But there were no signs of the first infection from two of the patients: the middle-aged man and the couple’s daughter. Even so, reinfection cases were considered for some reasons.

In the first case, the middle-aged woman was isolated at home and contracted a variant of the coronavirus that arrived in Brazil through travelers for the first time.

Her husband had contacted investigators for testing because he thought he had been infected by a co-worker who had traveled abroad.

Then the scientists concluded that only the middle-aged man could have transmitted the coronavirus to his partner.

And in the second infection, the two patients took a different strain than the one identified by the genetic test of the virus that infected the woman the first time.

The second case was considered a reinfection due to its connection with others, Moreno explains.

“It’s difficult to look at the domestic contact cases where two were reinfected in a fully documented way and look at the other two and ignore them because they didn’t have a sample of the first infection.”

Based on this finding, the scientists set out to investigate why these patients became ill again. They found an answer in an analysis of the antibodies that existed in the bodies of the four.

“What surprised us was to realize that, after the first infection, they did not have a sufficient level of neutralizing antibodies,” says Moreno.

This type of antibody prevents our cells from being infected by the coronavirus and is produced by one of two types of immune responses.

The first is the so-called innate immune response, a first line of defense that involves generic cells that act by detecting an invader. Sometimes this is enough to end the threat.

In turn, the adaptive immune response is one that the body develops specifically against a virus or bacteria.

It involves the production of antibodies and, at some point, an immune memory that will allow our body to protect us from the same pathogen when we become infected again.

But it takes a few days to develop and occurs when the disease is most severe and long-lasting.

Scientists believe that a mild COVID-19, in which the person is less ill, does not have time to generate an adaptive immune response, which generates neutralizing antibodies.

The four patients in the study who have few neutralizing antibodies are “unequivocal evidence,” Moreno says, that they did not develop an immune memory after the first infection.

“They had a very strong innate immune response in the first episode and controlled the infection. That was not enough to trigger the immune memory mechanisms generated by the adaptive response. This was only achieved after the second infection, when we detected an increase in neutralizing antibodies “. explains the scientist.

This shows that many may be wrong to think that it is okay if they already had covid-19. “It is not right, especially if it was a mild or very mild case, almost asymptomatic or asymptomatic,” says Moreno.

The scientist cautions that even those who did a serological test that indicated the presence of antibodies to covid-19 in their blood cannot be ignored.

He says the quality of this evidence is low for now. Serological tests for the new coronavirus are recent and not yet ideally accurate.

Therefore, they may fail to, for example, misidentify antibodies to other diseases as if they were antibodies to Sars-CoV-2.

Or they can also correctly signal the presence of antibodies to the new coronavirus, but these antibodies may not be neutralizing. To find out, you need a more complex test that commercial labs don’t do.

“A positive serological test is not an immunity passport,” Moreno warns.

The good news is that this research also indicates that a Covid-19 vaccine should be based on two doses, and that is already the case for many of the immunizers being investigated (and all those who have been proven effective). until now).

But the Fiocruz researcher says that the ideal interval between the first and second dose needs to be further investigated.

Additionally, he argues that scientific efforts from now on should focus on understanding how common covid-19 reinfection is.

“We no longer have to prove whether or not there is reinfection, because we already have a reasonable number of cases documented with all scientific rigor. We have to know what the frequency is in the general population because it is important to manage health policies. public health.”

Have you seen our new videos on Youtube? Subscribe to our channel!