For the nearly 100 million people worldwide who have been infected with the coronavirus, the new science offers some comfort: reinfections appear to be rare and you can be protected against Covid-19 for at least five months.
The study, the largest of its kind, followed more than 20,000 health professionals in the UK, testing them regularly for infection and antibodies. Between June and November, the researchers – from Public Health England (PHE) – found 44 potential reinfections among the 6,614 participants who had tested positive for antibodies or had a previous positive PCR or antibody test when they joined the study. (The full results have not yet been published, but PHE told Vox that a pre-press would soon be shared online.) Meanwhile, of the more than 14,000 people who tested negative for the virus at the start of the study, there were 409 new infections .
Only two of the 44 potential reinfections were designated as “likely” and the rest were considered “possible”, “based on the amount of confirmatory evidence available,” the health agency’s press release said. According to the BMJ, 15 people – or 34% – had symptoms.
Therefore, if all 44 reinfections are real, this translates into an 83% lower risk of reinfection compared to healthcare professionals who have never had the virus. If only two are confirmed, the protection rate rises to 99 percent. Either way, this means that natural immunity provides a level of protection similar to the approved Covid-19 vaccines.
As with vaccines, it is not yet clear how long immunity lasts after an infection. The antibodies may fade after five months or last much longer, something that the researchers behind the ongoing study, which will run for a total of 12 months, plan to investigate.
“This one [new] study provides some comfort that naturally acquired antibodies are quite effective in preventing reinfections, ”Akiko Iwasaki, an immunobiologist at Yale University, said Vox. The findings also fit into another article on health professionals, published in the New England Journal of Medicine in December: the researchers found that people who had antibodies to Covid-19 were more protected from the virus for six months than people who were 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, say in March-April 2020”.
People with the virus can still pass it on if infected again
The good news for individuals who have already had Covid-19 also comes with a warning about the risk that they may still pose to others. Although antibodies can protect against a second case of Covid-19 in most people, “the first evidence from the next phase of the study suggests that some of these individuals carry high levels of the virus and may continue to transmit the virus to others,” warned PHE in the press release.
“We now know that most of those who have had the virus and developed antibodies are protected against reinfection, but that is not total,” said Susan Hopkins, PHE’s senior medical consultant and study leader, in a statement, “and we still don’t know how much protection lasts. ”
In other words, even if you had Covid-19, although you are unlikely to get really sick again soon, you should still consider yourself a potential risk of spreading it to others if you catch the virus again and you may be asymptomatic. That means continuing to take precautions – how to wear masks and distance yourself socially, Iwasaki added. And it is one of the reasons why immunologists say that people who have already been infected with the virus must still prepare to receive the vaccine when their turn comes.
There is 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 variants of the coronavirus affect you?
Who is most likely to have a lasting immune response? We have some evidence that different individuals have different antibody responses after Covid-19 infections. And it is possible that factors such as sex and severity of the disease influence the strength of a person’s immune response.
For now, however, research suggests that survivors of the virus can only help us gain 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 a while to answer the question with authority.