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Approaching the 200,000 covid-19 death mark, Brazil was faced in early December with a new number related to the disease: the number of reinfection cases.
According to the Ministry of Health, as of this Monday (12/21), the country had two confirmed cases of reinfection and at least 58 suspected cases under analysis.
The ministry defines the situation of a person who tested positive in a PCR-type test for coronavirus as reinfection and, 90 days or more later, tested positive again – and in addition, the genome sequencing of the samples showed two different viral strains.
The new coronavirus has undergone almost two mutations per month, and these generate subgroups of viruses, the strains.
That is why genetic sequencing is so important to prove reinfection: it shows that it is two different infections, and not the “resurgence” or strengthening of the same infectious agent in a first disease.
In a country where the coronavirus has already sickened more than 7.2 million people and claimed the lives of more than 187,000, how should we view confirmation of reinfections? What risks do they pose to individuals and the direction of the pandemic?
Check out responses from experts, government agencies, and recently published research.
1. Cases registered in Brazil and around the world
At the moment, the little data available worldwide shows that reinfection is rare.
The Dutch news agency BNO News is collecting and publishing global data in this newspaper, until this Monday (12/21), the Covid-19 Reinfection Tracker platform registered 30 confirmed cases of reinfection in the world and 2,049 under suspicion.
Of the 30 confirmed cases, the mean interval between the first and second infection was 80 days. One resulted in death.
The first confirmed case in the world, in August, was that of a 33-year-old Hong Kong resident. He first had covid-19 in March, and then in August, 142 days apart. On the first occasion, he had mild symptoms; in the next, he was asymptomatic and only found out about the disease because he was tested at the airport. Their samples were subjected to PCR testing and genomic sequencing.
In Brazil, the Ministry of Health confirmed the first case of reinfection on December 10. A 37-year-old health professional from Natal (RN) had mild symptoms and a positive CRP in June and October. According to RN’s State Department of Public Health, she’s fine.
Later, a second case was confirmed in the country, by a 41-year-old nursing assistant from Fernandópolis (SP). He had symptoms in both infections and according to the municipality’s health secretary, Ivan Veronesi, he is fine.
Several municipalities and states are reporting reinfection episodes that have not yet been accounted for by the ministry, which it only does after analysis by its national reference laboratories, as it did for the cases of Natal and Fernandópolis.
However, according to Paola Cristina Resende, a researcher at the Oswaldo Cruz Institute’s Respiratory Viruses and Measles Laboratory (IOC / Fiocruz), many cases of reinfection will never be registered. For starters, many people in the country have never had PCR tests, let alone two, and with satisfactory storage.
“To perform genomic sequencing it is important to have a good quality sample, with a sufficient viral load. Sometimes this first sample collected there in April, for example, was stored in a freezer that varies greatly in temperature, because there was no longer a freezer. (adequate) or left at room temperature at some point. This can degrade the viral genetic material, it is easy to deteriorate this material ”, explains Resende, who works directly with the genetic sequencing of the virus.
“It is a reality in our country that it is difficult to store many samples. Many of them are being discarded.”
For the cases of samples in which there is a satisfactory quality and that are sent to national laboratories for confirmation of reinfection, the interval between the first infection and the second must be at least 90 days, but according to the investigator, that number is still there. in debate.
This is because there are already reports of longer and shorter reinfections around the world; In the BNO News survey, there are cases with an interval that varies between 10 days and 185 days.
2. Risks, individual and collective
Another indicator for which there is no pattern is the severity of the comparison between the first and second infection.
“There are published reports of more serious reinfections than the first time, but also cases like the first registered, asymptomatic (in the second infection, in Hong Kong),” says infectologist Raquel Stucchi, professor at the State University of Campinas (Unicamp) and consultant for the Brazilian Society of Infectious Diseases (SBI).
In fact, one of the first studies that collected cases of reinfection in the world, published in October in the scientific journal The Lancet Infectious Diseases, showed very varied images, since a 25-year-old man who had mild symptoms the first time and had than being hospitalized the second time. in the USA, a 51-year-old woman who presented mild manifestations in both cases in Belgium.
Stucchi recalls that, with symptoms or not, a reinfected patient can continue to transmit the disease to other people normally.
However, because they are apparently rare, experts believe that reinfections will not be able to carry out something like a second or third wave of covid-19 on their own; so far, these are being led by new cases.
3. The enigma of immunity
“If there is something that is still mysterious or that we have little knowledge about covid-19, it is in relation to immunity. There are questions that have not yet been adequately answered, such as why those with a mild condition may not develop antibodies,” says professor the Unicamp.
And, in cases of reinfection, this appears to be the case.
“Those who have a mild condition sometimes do not even have protection against the disease, or if they do, they make a small amount of antibody that lasts for a very short time,” explains the infectologist, noting that cases of reinfection have generally occurred with healthy people. without prior immunity deficiencies (immunosuppressed people), for example.
Our immune system defends itself on two fronts.
The first is always ready to act, as soon as a foreign agent is detected in the body: it is the innate immune response, which includes white blood cells and substances that cause inflammation in the body.
But this is a “generic” strategy, as opposed to the adaptive immune response, which is tailored to a specific invader, such as the coronavirus. One of the soldiers on that front is T lymphocytes, capable of attacking only cells infected by the virus.
It turns out that developing this adaptive response takes time; Some COVID-19 studies suggest that antibody production begins after 10 days. Therefore, there are doubts about whether asymptomatic people or people with mild symptoms develop this type of strategy.
If developed, adaptive immunity can leave a memory in the body that will prevent infections like that in the future.
This memory lasts more or less, depending on the disease. Measles is very memorable: a viral infection is capable of generating immunity for life. On the other hand, respiratory syncytial virus (RSV) can infect children several times in the same winter.
It is not yet known how long immunity to Sars-CoV-2 lasts, but six other coronaviruses may provide a clue. Four of them produce symptoms of a common cold and have a short-lived immune response, and patients are likely to be reinfected a year later.
A King’s College London study on the new coronavirus suggested that antibody levels against it decreased for three months.
For Paola Cristina Resende, everything indicates that the problem of reinfection is more related to the patient’s immune response than to the virus itself.
“Re-infection is not so much caused by the virus and how much it evolves, but by the individual and their ability to produce antibodies against the virus,” says the researcher at the Oswaldo Cruz Institute.
“The amount of virus circulating in the population is large and the possibility that an individual who has had the coronavirus is exposed (to the pathogen, again) as well.”
4. Lessons
For those interviewed by BBC News Brazil, although rare, reinfections reinforce a lesson for all.
“Many people who think that they have already taken covid-19 and that they are immune, and that this would be like a passport to abandon all preventive measures. The confirmation of reinfection cases (in Brazil) shows that not: while the virus circulate, we will need to maintain preventive measures and it will take a little longer to return to our normal life ”, highlights Resende.
Raquel Stucchi agrees.
“Those who had and did not have covid-19 should continue to wear masks, avoiding overcrowding, among other preventive measures,” concludes the infectologist.
* With information from André Biernath, from BBC News Brasil in São Paulo; and James Gallagher of BBC News.
