2023-09-13 09:08:25
Nearly one in three people exposed to SARS-CoV2 is infected, and even up to four in ten with the Omicron variant. In the case of immunity – conferred by vaccination, infection or a combination of the two – this rate drops to one in ten, according to a Geneva study published in the journal Nature Communications.
A team from the University and University Hospitals of Geneva (UNIGE/HUG) looked at the epidemiological data collected in the canton. More than 50,000 cases and 110,000 contacts recorded from June 2020 to March 2022 were analyzes.
“Our objective was to evaluate the secondary attack rate of SARS-CoV2, that is to say the proportion of infected people among the contacts of a sick person,” indicates Delphine Courvoisier, assistant professor at UNIGE and epidemiologist at HUG, cited Tuesday in a press release from the two institutions.
On average, a person infected just over three in ten of their contacts, mainly within the family unit, and up to four in ten with Omicron. However, immunity drastically reduces the number of infected contacts, mainly by protecting once morest infection and, to a lesser extent, by reducing the infectivity of infected people, explains in La Matinale on Wednesday Denis Mongin, first author of the study and substitute assistant professor at the University of Geneva.
“Immunity tends to disappear over time. Regarding protection once morest infections, this time seems to be around six months for vaccination and around a year for past infections. But this time varies depending on the ability of new variants to evade immunity.”
“What our study shows is that the reduction in infectivity conferred by vaccination or past infection appears more robust over time,” he adds.
These results confirm what had already been observed: immunity following an infection has a stronger effect on the transmission of the virus than the vaccine, whether on the reduction of contagiousness or the risk of contamination.
“Significant risks”
“However, the risks associated with infection are significant, particularly for fragile people. We also know that there are cumulative risks associated with multiple infections, particularly cardiac or neurological,” emphasizes Delphine Courvoisier.
Denis Mongin also reminds that being infected remains risky.
“There are of course risks of severe Covid but in addition there is long Covid. Each infection potentially induces damage to the immune system, cardiac and neurological damage. It is therefore wise to avoid infections.”
In addition, analysis of Geneva data shows that age, sex, socio-economic status or obesity have little impact. Likewise, the combination of vaccination and infection also did not confer superior immunity. And in all cases, the protective effect fades within a few months.
At present, the vaccine remains of interest by limiting contagiousness, in particular for healthcare workers and very elderly and/or fragile people. But it cannot constitute the only public health measure in the event of a new wave, the authors conclude.
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