By Nermeen Nabil Khear 
With the rise of omicron came the fall of long-lasting protection from reinfection with the pandemic coronavirus SARS-CoV-2, according to a study published in Nature.
Using population-wide data from Qatar, researchers found that a COVID-19 infection from a pre-omicron variant of SARS-CoV-2 (such as alpha or delta) yielded around 80 percent protection from reinfection with another pre-omicron variant—and that level of protection lasted over the course of at least a year. But, things changed in late 2021 with the emergence of omicron, which still reigns supreme today. According to the data, an infection with omicron provided an initial protection of nearly 80 percent between the first three to six months after infection, but that protection rapidly declined. Between nine months and a year, protection fell to around 27.5 percent, then dropped to a negligible 5 percent after a year.
Effectiveness of previous infection against reinfection.
Credit:
Chemaitelly et al., Nature, 2025
The results of infection-derived protection were similar regardless of whether people were vaccinated or unvaccinated, a sub analysis found. The study did not evaluate vaccine efficacy. A study published last year in the New England Journal of Medicine estimated that the 2023-2024 mRNA COVID-19 vaccines were 52 percent effective at preventing infection after four weeks, with effectiveness falling to 20 percent at 20 weeks (a little over four and half months).
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This articles is written by : Nermeen Nabil Khear Abdelmalak
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