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One coronavirus infection wards off another — but only if it’s a similar variant

With the dominance of the Omicron BA.5 variant here in the US and several incidences of reinfections among fully vaccinated and prior infected individuals, scientists are looking deep into whether there is any protection at all among the people having the natural immunity induced by infection with SARS-CoV-2 and if so for how long. A recent study suggested that the natural immunity induced by infection with SARS-CoV-2 provides a strong shield against reinfection by a pre-Omicron variant for 16 months or longer. It also showed that the immunity triggered by the previous infection also thwarts the development of severe COVID-19 symptoms, and fortunately this safeguard shows no signs of waning.

In one of the first studies of its kind, scientists from Qatar analyzed the entire Qatari population and compared COVID-19 cases in unvaccinated individuals who’d had one previous SARS-CoV-2 infection with cases in unvaccinated people who’d never previously been infected. They found that infection with a pre-Omicron variant prevented reinfection by another pre-Omicron variant with an average effectiveness of 85.5% for the period covering the 4th through the 16th month following the initial infection. Although not conclusive, this study affirms the substantial evidence for natural immunity’s capabilities and urges further exploration.

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