Anyone who has been infected with Sars-CoV-2 at least once has therefore built up a high natural immunity against a serious form of covid-19, i.e. against hospitalization and death. Level and duration of protection against re-infection, symptomatic disease and severe disease are at least comparable to two doses of the mRNA vaccines for the parental, alpha, delta and omikron BA.1 variants of the virus.
This is the main conclusion of a review annex meta-analysis of 65 studies conducted in nineteen countries, the results of which were presented in The Lancet by the so-called COVID-19 Forecasting Team. Never before has it been assessed on such a large scale how durable the protection is after natural infection against the different virus variants.
The protection against re-infection by a pre-omikron variant is about 85 percent after one month and that drops to 79 percent after ten months. Protection against infection with a pre-omikron variant against re-infection with the omicron BA.1 variant was lower (74% after one month) and decreased more rapidly to 36% after about ten months. But protection against hospitalization and death remained universally high for 10 months: 90 percent for the original, alpha, and delta variants, and 88 percent for omikron-BA.1.
According to the researchers, their findings confirm the results of previous reviews, and in vitro and model studies: immunity due to infection involves both humoral and cellular responses, which as a whole can lead to increased protection against the different covid-19 variants. The fact that there is a weaker cross-immunity with the omikron BA.1 variant and its sublines also supports this picture: after all, spike protein mutations make omikron, compared to other variants, slightly better able to evade the built-up immunity.
The researchers do point out some limitations of their study. For example, they report that the number of studies on the omikron BA.1 variant and its sublines and the number of studies originating from Africa were generally limited. In addition, the paucity of data on protection caused by previous infection of the omikron BA.1 variant and its sublines (BA.2, BA.4 and BA.5) emphasizes the importance of ongoing monitoring, they say. Also in the knowledge that an estimated 46 percent of the world’s population will be infected with the omikron variant between November 2021 and June 2022.
Commenting, South African epidemiologists Cheryl Cohen and Juliet Pulliam note that the results of the meta-analysis suggest that, as with other human coronaviruses, there will be a low seasonal hospitalization for SARS-CoV-2 going forward. .