How long does natural immunity to Covid last? How long are the antibodies produced by the body after encountering Sars-CoV-2 able to protect us from reinfection? According to a new study being evaluated for publication in the journal Nature conducted to Vo ‘Euganeo, in Veneto, by Andrea Crisanti, microbiologist at the University of Padua, natural antibodies persist at least 9-10 months.

Not only. Who among the healed of the first wave was directly exposed during the second wave to Covid-19 did not get sick again. The survey involved 125 residents in Vo ‘Euganeo and fractions (88 swab positive in February 2020, the other positive serological test results during the May controls).

What we have seen that the antibodies, mostly neutralizing, remain in circulation for up to 10 months, without substantial differences in the antibody titre between symptomatic and asymptomatic or even between age classes, summarizes Crisanti, who collaborated with colleagues from Imperial College London.

The study therefore seems to suggest that there is one rather durable protective barrier for those who have encountered Sars-CoV-2, even for those who have shown no symptoms.

No reinfection

Vo ‘Euganeo represents a case study since the beginning of the pandemic. Not only because it registered the first Covid victim in Italy, but also because its 3200 inhabitants were tested several times with swabs and serological analyzes. In this last round of tests carried out in November, unlike the previous occasions they participated only the 125 residents that last May, following the outcome of the venous sampling, they had shown the presence of antibodies against Covid, with the infection dating back to February-March. As expected, the antibodies decrease after nine months, although they remain quite high – adds the professor – but the interesting and above all reassuring aspect that 18 people were exposed to positive Sars-CoV-2 during the second wave because they shared a house or had close relationships: none of them got sick again. We know with certainty that these people have come into contact with the virus again because their antibody levels have risen, as if they had the vaccine booster, but they did not get sick, and this is great news.

The increase in antibody production means that who is infected and healed in some way protected. But the virus in order to stimulate the antibody responses of these people – says Crisanti – multiplied a little, we don’t know how much, but it certainly had a replication phase that did not lead to the disease, but that caused aasymptomatic transient infection, because otherwise the immune response would not have been stimulated.

Is it contagious at this stage? one of those questions that has not yet been answered and further investigation will be needed.


The duration of immunity (natural and induced by vaccines) is one of the most debated questions that still does not have definitive and univocal answers. Understanding the mechanisms for it is of fundamental importance to plan vaccination campaigns, even with any recalls, and to resume a normal life.

Some studies speak of natural immunity of 3-5 months, others, more numerous, go up to 8-9 months. It is clear that the more time passes, the more we will be able to have precise information even if the response of the individual is very important. Caution, not everyone who becomes infected develops neutralizing antibodies.

As the immunologist explains Antonella Viola, professor of Pathology at the University of Padua according to a study carried out in China, only 40% of HIV-positive people, who have generated antibodies against Sars-CoV-2, produce antibodies capable of blocking the virus.

March 29, 2021 (change March 29, 2021 | 09:11)

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