Natural immunity after Covid-19 could last at least 5 months

For the nearly 100 million people around the world who have been infected with the coronavirus, new science offers some comfort: Reinfections appear to be rare and you can be protected from Covid-19 for at least five months.

The study, the largest of its kind, followed more than 20,000 health workers in the UK, testing them regularly for infection and antibodies. Between June and November, the researchers – from Public Health England (PHE) – found 44 potential re-infections out of the 6,614 participants who had tested positive for antibodies or had previously had a positive PCR or antibody test when they were joined the study. (Full results are yet to be released, but PHE told Vox that a preprint will soon be shared online.) Meanwhile, of the 14,000 and more people who tested negative for the virus at the start of the study, there were 409 new infections. .

Only two of the 44 potential re-infections were rated “probable” and the rest were considered “possible,” “based on the amount of confirmatory evidence available,” the health agency press release said. According to the BMJ, 15 people – or 34% – had symptoms.

So if the 44 re-infections are real, that translates to an 83% lower risk of re-infection compared to health workers who have never had the virus. If only two are confirmed, this protection rate rises to 99%. Either way, this means that natural immunity provides a level of protection similar to that of approved Covid-19 vaccines.

As with vaccines, the duration of immunity after infection is not yet clear. The antibodies can wear off after five months or last much longer, which the researchers behind the ongoing study, which will last a total of 12 months, plan to study.

“This [new] The study provides some comfort that the naturally acquired antibodies are quite effective in preventing re-infections, ”Akiko Iwasaki, an immunobiologist at Yale University, told Vox. The findings are also consistent with another article on health workers, published in the New England Journal of Medicine in December: Researchers found that people who had anti-Covid-19 antibodies were better protected from the virus for six months than people who did not.

That said, Iwasaki said: “You can also interpret this data to mean that protection against reinfection is not complete – especially for people who had Covid during the first wave, for example in March-April. 2020. “

People who had the virus may still be able to transmit it if they are re-infected

The good news for people who have had Covid-19 also comes with a warning about the risk they may still pose to other people. While the antibodies could protect against a second case of Covid-19 in most people, “early evidence from the next stage of the study suggests that some of these people carry high levels of the virus and may continue to transmit the virus to others, ”PHE warned. in the press release.

“We now know that most of those who have had the virus and have developed antibodies are protected against reinfection, but that is not total,” said Susan Hopkins, senior medical advisor at PHE and head of the study, in a press release. and we don’t know how long the protection lasts yet. ”

In other words, even if you have had Covid-19, while it is unlikely that you will be really sick again anytime soon, you should still consider yourself a potential risk of passing it on to others if you catch the virus again and could be asymptomatic. . That means continuing to take precautions – like wearing a mask and social distancing, Iwasaki added. And this is one of the reasons immunologists have said that people who have already been infected with the virus should always plan to be vaccinated as well.

There is also still a lot we don’t know about immunity after Covid-19: how exactly does it compare to immunity after vaccination? How will the new coronavirus variants affect it?

Who is most likely to have a lasting immune response? We have evidence that different individuals develop different antibody responses after Covid-19 infections. And it’s possible that factors such as gender and disease severity influence the strength of a person’s immune response.

For now, however, research suggests that virus survivors might just help us achieve herd immunity faster – if their immunity lasts long enough. But since the virus has only been known to humans for a little over a year, it may take some time to authoritatively answer the question.