Individuals previously infected with SARS-CoV-2, the virus that causes COVID-19, still benefit from vaccination, gaining 60% to 94% protection against reinfection, depending on the variant. A new study led by Katrin Weindrup Nielsen at the Statens Serum Institute, Denmark, publishes these findings November 22 in the journal Open Access. PLOS medicine.
During the recent pandemic, vaccination was one of the best tools available to reduce the spread of COVID-19. People infected with the virus are known to develop natural long-term immunity, but Finderup Nielsen and her team wanted to see if these individuals would benefit from receiving the vaccine. The team analyzed infection and vaccination data from nationwide Danish registries that included all people living in Denmark who tested positive for the virus or were vaccinated between January 2020 and January 2022. The dataset included more than 200,000 people who tested positive for SARS-CoV-2 during all of Alpha, Delta and Omicron waves. Their analysis showed that for people with previous infections, vaccination provided up to 71% protection against reinfection during the alpha period, 94% during the delta period and 60% during the omicron period, with protection lasting up to nine months.
These results show that vaccination protects people against SARS-CoV-2, in addition to the protection provided by natural immunity during all three waves of variants. The authors point out that the current study was too short to determine whether the vaccine protects against severe outcomes, such as death and hospitalization, and that future studies with longer follow-up times will be necessary to answer this question. From a public health perspective, these insights into vaccine effectiveness can help decision-makers plan the timing and implementation of vaccination strategies to make them more effective.
Finderup Nielsenadds, “In our study we found a significant efficacy of the vaccine against re-infection with SARS-CoV-2, and this shows the importance of vaccination also for those who may be protected with natural immunity.”
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