COVID-19: Recovered people are immune for months, but there is a high risk of infecting others, study finds

Most people who contract COVID-19 and recover are likely to be immune for several months afterwards, as detected by a study called MERMAID which involved over 20,000 UK healthcare workers and was published in The Lancet.

The study concluded that Immune responses to a previous infection reduce the risk of re-contracting the virus by 83% for at least 5 months.

“Over the past year, reports of repeated infections with SARS-CoV-2 have weakened confidence in the immune system’s ability to maintain its defenses against the virus. The interim results of the study alleviate some of these fears, ”explained the principal investigator. Susan Hopkins, Senior Medical Advisor to Public Health England in London. The data suggests that natural immunity could be as effective as vaccination, at least during the five-month period covered by the study so far. “

Data suggests repeated infections are rare: they occurred in less than 1% of about 6,600 participantsif they had previously had COVID-19. But the researchers also found that People who are re-infected can carry the virus in their nose and throat, even when they have no symptoms. “Such viral loads have been associated with a high risk of transmitting the virus to others,” noted Hopkins.

“Reinfection is quite unusual, so that’s good news,” as assessed by immunologist John Wherry of the University of Pennsylvania in Philadelphia. Although he warns that “It does not imply being free to walk without a mask.”

SIREN is the largest coronavirus reinfection study systematically detecting asymptomatic infections. Every two to four weeks, participants undergo blood tests to detect anti-SARS-CoV-2 antibodies, as well as PCR tests to detect the virus itself.

During the 5 months, the team found 44 possible re-infections. In the group of 14,000 participants who had not been infected previously, 318 people tested positive for the virus.

“Some of the re-infections are still being evaluated”, Hopkins explained. All 44 are considered “possible” re-infections and have been classified based on PCR testing combined with screening measures to reduce the risk of re-detection of the virus from the original infection. So far, only 2 of those 44 cases have passed more stringent testing to be classified as ‘probable’. The study did not assess whether symptoms were better or worse during the second infection than during the first, but Hopkins notes that “Only about 30% of people with possible re-infections reported symptoms, compared to 78% of participants with first-time infections.”

At the moment, the team does not have enough data to determine who might be at higher risk of re-infection.. Immunologist George Kassiotis of the Francis Crick Institute in London notes that study participants were mostly women, and mostly under the age of 60. “This group is unlikely to experience the most severe form of COVID-19, and may not be representative of the population as a whole.”

Researchers are always collecting data; hopes to get a feel for the duration of immunity and study the effects of a variant of SARS-CoV-2 called B.1.1.7 which appeared in 2020 and quickly spread across the country. “While there are many reasons to suspect that existing protection should cover new variants, it is possible that immune responses generated against one variant are less effective against another,” Kassiotis concludes. It’s still an open question. “

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