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These cases are still considered rare and difficult to confirm, but cases of reinfection are also known to be possible. There are only 26 confirmed cases in the world, but many hundreds of suspects, in a list where we could find the already reported cases of three patients in Portugal who may have been infected twice. For confirmation, however, virus sequencing results are needed which show the person was infected with two different variants. Scientists still don’t know what the burden of reinfections is in the outbreak, but if it proves that – as with dengue – the second infection with a new version of the virus is more aggressive than the first, these cases may impact the effectiveness of the vaccines that are (or have been) developed.
As with the other numbers associated with SARS-CoV-2 infection, the number of reinfection cases also increased. Worldwide, after a first officially confirmed case in Hong Kong in August, there are now 26 confirmed reinfections, according to the Dutch tracker (covid-19 reinfection tracker) which records these cases in detail. However, there are also more than 570 suspected cases from situations where an infected patient recovered, performed a negative test, but some time later the test returned to give a positive result. At least three of these suspects concern patients in Portugal, but confirmation of reinfection will only be possible with the result of tests for sequencing the virus.
For a case to be considered a suspected reinfection, a patient must have undergone a positive reaction test (PCR) twice with at least one month without symptoms in between. For confirmation, more than that is needed. “To be validated, they must be confirmed by sequencing the virus and demonstrate that they have a sufficient number of mutations to prove that the first infection is far enough away from the second”, confirms to the PUBLIC geneticist Luísa Pereira, researcher at the Institute of Research and Innovation in (I3S) of the University of Porto. The 26 confirmed cases passed these tests, and many have even been described as sequencing results published in scientific journals.
But if it is not reinfection, what other explanation can there be for a person to get sick again? “There are viruses that have this ability to be latent in our body and not manifest themselves, go unnoticed by the immune system and there are no symptoms. It is not yet proven that this virus does not have this ability ”, explains the scientist. Viruses, he clarifies, can wake up in a person’s body, fall asleep, and then wake up again. But, in these cases, it would not be a new infection, but all the same with a peculiar dynamic.
“There are several very prolonged cases, more than 90 days, of people who alternatively have a positive, negative, again positive, still negative result. These people think that there is continuity in the presence of genetic material from the virus that first infected her, ”says Luísa Pereira.
These unstable results may be associated with problems in specimen collection, but they may also be related to the progression of infection in the body. At some point, the virus may no longer be in an integral (and infectious) particle, but it will still release remnants of the genetic material that will be enough, in some cases, to give a positive result. How long can this effect last? It is not yet known. “The tests carried out show that, in principle, by the majority of successive samples, the virus can no longer be cultivated in the laboratory, which indicates that it might be only a remnant of the genetic material and not the intact virus,” explains geneticist.
Another thing that is still unclear is the relationship of these reinfection cases to the severity of the disease and this is where we can face serious obstacles to vaccine effectiveness. Although some of the officially confirmed cases involve situations with mild symptoms of the disease, there are also people who have seen their health condition worsen from the first to the second infection. “As with other viruses, such as dengue fever, for SARS-CoV-2, many of the severe symptoms of the disease are associated with an exaggerated response from our immune system,” confirms Luísa Pereira, referring to the cytokine storm in response to the virus getting worse the condition of an infected patient.
In fact, the researcher says this similarity to dengue fever can lead to even more serious problems. It is that, says the scientist, that today there are four strains of dengue (there is a fifth that emerges) and that when someone is infected with one strain they are immune for life against that, but when they become infected with another different strain , gets sick much more seriously. “This can happen for SARS-CoV-2,” he admits, stating that if this hypothesis occurs with covid-19 it can have a major impact on vaccine efficacy.
Basically, by immunizing a person for a particular variant of this virus, we could make that person react much more seriously to a later infection with a different version. “We don’t know yet if this is what we will see with SARS-CoV-2, but if confirmed, it has serious implications for vaccination,” says Luísa Pereira, who doesn’t want to be an alarmist and also recalls that one of the challenges of dengue was precisely to ensure protection against the four strains.
In the first known case of reinfection (in Hong Kong), the man eventually developed milder symptoms in the second infection, but in another case also published in a scientific journal a man living in the USA saw his health deteriorate. notably in the second infection.
Monitoring SARS-CoV-2 around the world is not easy, with the virus accumulating hundreds of mutations, most of which have no significant effect on the outcome of infection or viral contagion. In fact, many of these mutations only occur in the infected person without spreading to other individuals. However, this coronavirus has already changed its genetic “presentation” enough for scientists to separate it into five distinct groups. They are called 19 A, 19 B, 20 A, 20B and 20 C.
It is too early to say that we are facing five different strains of the same virus, explains geneticist Luísa Pereira, but they will at least be different versions or variants that will circulate at different times and in different areas. Thus, if groups 19 A and 19 B are associated with viruses present in the China region, 20 A and 20 B were already the most present variants in Europe and, finally, 20 C will have been most present in the US and Europe. South America.
There are still many unanswered questions related to these reinfections reported around the world, their importance and impact on vaccination strategy and pandemic management. But the fact is that cases are piling up that until now could have been considered rare. Luísa Pereira notes that, if the three suspected cases in Portugal were confirmed, the truth is that three situations in a context in which “only” less than 3% of the population has been infected would not be so rare, other than the cases of reinfection that they may have gone unnoticed, being asymptomatic or seen as a more prolonged illness.
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