Natural immunity to Covid-19, the one that causes the disease itself, could last at least 1 year. This is suggested by long-term data from a study carried out in the north of Italy, a severely affected area during the first days of the pandemic, showing that reinfection is a very rare phenomenon.
“Natural immunity to SARS-CoV-2 seems to confer a protective effect for at least one year, which is similar to the protection reported in studies carried out with people who have received vaccines,” concludes the team led by Nicola Mumoli, from the Fornaroli Hospital. in Magenta.
The findings, which are based on medical records from more than 15,000 people, “JAMA Internal Medicine” is published.
However, as an editorial accompanying the report warns, despite the encouraging results, people who have passed the Covid-19 should be vaccinated.
“First, we don’t know how long natural immunity lasts,” he writes. Mitchell Katzfrom NYC Health and Hospitals. Furthermore, it is not clear how much natural immunity protects against new variants of SARS-CoV-2.
In addition, “there is a social benefit,” adds Katz..
“Achieving herd immunity through natural infection is a long and painful process and, historically, the only human disease that can be eradicated, the smallpox, was eradicated through vaccinationnot the natural infection, “he said.
In the Italian study, reinfection was defined as the appearance of a new infection at least 90 days after the ‘complete resolution of the first infection’, to ensure that there was no confusion about the traces of the first infection that persisted in the tests.
The Italian team tracked new infection rates among more than 15,000 residents of the Lombardy region of northern Italy, using PCR tests obtained in early 2020 through the end of February 2021.
Almost 13,000 had tested negative for Covid-19 in their initial tests, while 1,579 were positive.
About a year later, 3.9% of people who had never tested positive for Covid-19 acquired a coronavirus infection.
In contrast, only 0.31% – five people – of those who had been previously infected suffered a reinfection. Four of the five patients worked or visited hospitals, suggesting that they had an especially high potential exposure to the virus. Only 1 in 5 reinfected patients was sick enough to require hospitalization.
What’s more, reinfection usually occurs only after a long time: The average time from initial infection to reinfection was 230 days, Mumoli and his colleagues found.
But the researchers emphasized that none of this means that previously infected people should stop getting vaccinated.
They also acknowledge that their study “ended before the SARS-CoV-2 variants began to spread, and it is unknown how natural immunity responds to the virus. [original] before the variants ».