Immunity acquired after infection with the SARS-CoV-2 coronavirus offers good protection against illness — and risk of hospitalization and death — for at least ten months, indicates a study released this Thursday. The risk of serious illness is 88% lower compared to someone without immunity.
The work published this Thursday in cientific magazine The Lancet constitutes the “most comprehensive” analysis made so far on the level of protection after being infected by different variants of that virus, although it does not include data on infection with the variant Omicron XBB and yours underlines.
The researchers indicate, on the other hand, that infections with pre-Omicron variants provided a “substantially reduced” natural immunity against reinfection with the Omicron strain BA.1., where ten months after the first infection the protection was only 36 %.
65 studies from 19 countries were reviewed and analyzed, which compare “the reduction in the risk of covid-19 between unvaccinated individuals against a reinfection by SARS-CoV-2 and unvaccinated individuals without previous infection until September 2022”, says a statement. dissemination of the study.
According to research, the level and duration of immunity “against reinfection, symptomatic disease and severe disease” are at least equal to those provided by two doses of mRNA vaccines (Moderna, Pfizer-BioNtech) for the Alpha, Delta and Omicron BA.1.
“Vaccination is the safest way to achieve immunity, while achieving natural immunity (through contagion) must be weighed against the risks of serious illness and death associated with the initial infection,” says Stephen Lim of the Institute for Metrics and Evaluation in Health (IHME) at the University of Washington School of Medicine, in the United States, the lead author of the analysis, cited in the statement.
Caroline Stein, also from IHME and co-author of the study, points out that “vaccines remain important for everyone” to protect both high-risk populations, such as those over 60 and those who already have other diseases.
“This also includes populations that were not previously infected and unvaccinated groups, as well as those that were infected or received the last dose of the vaccine more than six months ago”, he adds, arguing that natural immunity and the situation in relation to vaccination must be taken into account to “get a complete picture of an individual’s immunity profile”.
Since January 2021, several studies have been released on the effectiveness of SARS-CoV-2 infection in reducing the risk of re-infection and on how immunity wanes over time, but none have comprehensively assessed how long protection would last after infection. natural infection against different variants.
Analysis of data from 21 studies on infection with a pre-Omicron variant “estimated that protection against re-infection of a pre-Omicron variant was around 85% in the first month and dropped to around 79% after 10 months” , while the natural immunity achieved with “an infection of the pre-Omicron variant versus re-infection of the Omicron BA.1 variant was lower (74% at one month) and declined more rapidly to 36% at about 10 months”.
“However, analysis of five studies reporting serious illness (hospitalization and death) revealed that protection at this level remained universally high over 10 months: 90% for alpha and delta ancestors and 88% for Omicron BA.1.”
Another six studies that evaluated protection specifically against Omicron variant sublines (BA.2 and BA.4/BA.5) indicated that protection was significantly lower when the previous infection was of a pre-Omicron variant, but that it remained “a higher level” when the previous infection was due to the Omicron strain, according to the study released Thursday.
According to another of the co-authors of the study, Hasan Nassereldine, from IHME, the lower protection from infections with the ancestral strains in relation to the Omicron variant and its sublines reflects the mutations that occurred and that allow them to “escape from acquired immunity more easily than than other variants”.
“The limited data we have on the protection of natural immunity from the Omicron variant and its sublines underscore the importance of ongoing evaluation, particularly as they are estimated to have infected 46% of the population worldwide between November 2021 and June 2022 “, says the scientist, adding that more research is also needed to “evaluate the natural immunity of emerging variants and analyze the protection provided by combinations of vaccination and natural infection”.
The authors of the study “Protection of infection with SARS-CoV-2 against reinfection: a systematic review and meta-analysis” warn that the work has some limitations, as data on the Omicron BA.1 variant and its underscores, as well as how about situation in Africa.
They add that calculations on protection may also have been influenced by data available beyond ten months after the initial infection. be limitedas well as the incomplete or inconsistent recording of information, for example, about a previous infection or hospital admissions.
Since June 1, 2022, the covid-19 pandemic is estimated to have caused 17.2 million deaths (6.88 million of which were registered) and 7.63 billion infections and reinfections, according to the study, which adds that “a large proportion of these infections occurred after November 14, 2022”.
“The immunity conferred by infections should be weighed alongside the protection gained from vaccination in assessing the future burden of COVID-19, providing indications on when individuals should be vaccinated and on policies that make vaccination mandatory for workers or restrict the access to places where the risk of transmission is high (…), based on the immune status”, the study also mentions.