Having Covid-19 doesn't necessarily protect against a second infection

According to a British study, protection could drop after six months, especially among those who have had asymptomatic Covid-19. An Italian study, on the other hand, indicates that in some cases it could be considered (for the future) whether to postpone the vaccination of the recovered after 10 months. The debate remains open and the numbers are still limited

(photo: MasterTux via Pixabay) We often talk about the vaccination of the recovered, or people who have already contracted Covid-19, symptomatic or asymptomatic, on when and how it is appropriate that receive the vaccine. A study by the University of Oxford highlights the fact that having the coronavirus does not necessarily protect against a new infection for long, especially when it comes to new variants, such as the delta, classified by WHO as variants of concern. In particular, the coverage may fall off as early as 6 months. Therefore, it is good to get vaccinated within that period, as also recommended by our current guidelines. Another research, conducted by the Irccs Irccs Sacro Cuore Don Calabria of Negrar di Valpolicella (Verona), confirms that for those who have had Covid-19 a single dose of vaccine is sufficient and indicates that in some cases, especially for those recovered from Symptomatic Covid-19, one might think to shift the dose even 10 months after infection, a slightly different result from the English one. Here's what we know and how to understand a little more.

The English study

Both studies involved small groups of participants, and also for this reason the conclusions reached by the research can be - in this as in other cases - slightly different. The researchers of the Oxford group have carried out a still limited survey, given that it is based on data from a small sample of 78 people, and not yet peer-reviewed - but we can read it in preview (preprint). The authors measured the immune response, both that linked to specific antibodies against Sars-Cov-2 and that of B and T cells. The answers differ greatly from person to person. In the cases of symptomatic Covid-19, after 6 months about 26% of people no longer showed the presence of specific antibodies against Sars-Cov-2, while among the asymptomatic it reaches 92%.

I The researchers then combined the results with tests performed using machine learning algorithms to better understand whether the severity of the disease correlates with subsequent immunity. With this method, the researchers identified a particular feature, such as a signature, in the immune response, one month after infection, which provides clues - it is a predictor - of the immunity present after 6 months. Deepening this result could be useful, in the future, to better study the duration of immunity.

From our guidelines to the Italian study

Currently, in fact, the Italian guidelines provide that those who tested positive for Sars-Cov-2 in the past receive a first dose of the vaccine somewhat distant from the infection, at least 3 months after infection, but no later than 6 months. The research conducted by the Negrar group of Verona, coordinated by Zeno Bisoffi, could in the future pave the way for a revision of these rules. The study involved nearly 2000 healthcare professionals and hospital staff, of whom 232 had previously had Covid-19, and was carried out in the first period of the vaccination campaign, from January to March 2021. The results are under review by the journal Clinical Microbiology and Infection (we don't have a preprint in hand). All participants received at least one dose of Pfizer-BioNTech's vaccine.

“Of the 1935 participants,” comments Bisoffi, director of the Negrar Department of Infectious and Tropical Diseases and Microbiology, “232 had a history of infection documented: precisely in the latter the average antibody titre after a single administration of vaccine was significantly higher than that found in those who had never contracted the virus and had received two doses of the vaccine ”. The response was stronger in young people, women and those who had Covid-19 with symptoms. This, continues the expert, confirms and supports the decision (already in progress) to proceed with a single administration in those who have already had Covid-19. But that is not all. "With surprise - adds Bisoffi - we observed that the antibody response was stronger the more time had passed since the infection, up to 10 months". For this reason, experts speculate that the first administration in those who have had Covid-19 could also be moved from current guidelines, which require the dose to be administered within six months. Obviously for now there is no indication to postpone the vaccination, also considering that each case is unique and that the protection from new variants could be reduced if the dose is delayed.


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