A meta-analysis published in “The Lancet” examined the level of protection conferred by past infection against the risks of asymptomatic, mild and severe forms of Covid-19 compared to people who had not been infected or vaccinated.
This study was conducted by an American working group coordinated by the Institute for Health Metrics and Evaluation (IHME) of the Washington School of Medicine, and compiled the results of 65 studies carried out in 19 countries. Although the subject is not new, this study is remarkable for its scope and for the fact that it is the first to include the Omicron BA.1 variant in its analysis. Studies integrating the protection conferred by hybrid immunity were excluded. The most recent data is from September 2022. The study did not include data on infection with Omicron XBB and its sublines.
History of infections is associated with reduced risk of Covid-19
It shows that the protection provided against severe forms by past infection is high for all variants, at 90.2% for the ancestral strain as well as the Alpha and Delta variants, and at 88.9% for Omicron BA.1 at 10 months.
Regarding the risk of reinfection with pre-Omicron variants, the study shows that protection by natural immunity decreases over time, but remains at 78.9% at 10 months. This protection declines more rapidly against Omicron, with a rate of 36.1% at 10 months, reflecting the widely described immune escape in 2022.
An individual’s immune profile depends on natural immunity and vaccination status
The authors found that the protection conferred by a past infection was equivalent to, or even slightly longer than, that conferred by two doses of mRNA vaccines.
This information is rich in lessons for more accurately assessing an individual’s immune profile, which depends on both their vaccination status and their “natural” immunity. It should guide public policies to adapt vaccination schedules according to past infections and individual risk factors.
This study clearly positions a possible Health PASS as fairer than a vaccination PASS. It also gives hope that the next waves of contamination will be less and less burdensome on health systems.
Is the interest of vaccination questioned?
The authors clearly underlined that no one should rely on a SARS-COV-2 infection to protect themselves against the risks it induces of severe forms, long-term COVID or complications for polypathological patients or patients with risk factors.
Pr Zureik, president of EPIPHARE gives his point of view on the subject on Twitter :
« But if protection by infection is equivalent to vaccine protection, some may wonder if it would not be better to catch Covid than to be vaccinated. The answer is clear: NO, NO, NO!
No, because the risks of serious complications with the vaccine are extremely low. This is not the case with infection. With infection, 4 risks are accumulated: risk of serious forms during the acute phase, risk of contaminating vulnerable people, risk of developing long-term Covid and the risk of developing serious complications in the medium and long term on several systems in particular. cardiovascular. The long Covid and the complications do not only concern the elderly and frail.
We should not therefore play Russian roulette with the infection which is much more dangerous than vaccination. »
« If the infections were mild like colds, we wouldn’t worry about this virus anymore. But if not, anything to prevent them is good to take, including vaccination as long as serious adverse effects remain extremely rare.“Explains Mircea T. Sofonea for Le Parisien
For IHME co-author Dr. Caroline Stein “Vaccines continue to be important for everyone to protect high-risk populations, such as those over 60 and those with comorbidities. This also includes previously uninfected populations and unvaccinated groups, as well as people who were infected or received their last vaccine dose more than six months ago. Decision makers must consider both natural immunity and vaccination status to get a full picture of an individual’s immunity profile. »
Limits of the study
The authors of the study acknowledge certain limitations to their work:
- the number of studies examining the Omicron variant and its sublines is relatively small, which could affect the precision of the results and which justifies further analyzes taking into consideration the fact that approximately 46% of the population worldwide was infected with Omicron between 11/15/2021 and 06/01/2022.
- Past infection status and hospital admissions were measured differently or were incomplete, which could bias the estimate of protection.
- Data beyond 10 months after initial infection were limited.
- Studies examining natural immunity in combination with vaccination (i.e. hybrid immunity) were excluded from the analyses. However, another study published recently in THE LANCET established that hybrid immunity conferred the best protection against all forms of Covid-19.
Despite these limitations, the study provides strong evidence for the durability of natural immunity against serious infections and is instructive for refining public health policies. Vaccination remains the safest way to protect against all serious forms of Covid-19. Prevention measures, such as wearing a mask, social distancing and air purification remain essential to slow the spread of the virus.
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