People who have had COVID-19 gain 60% to 90% protection against reinfection if they have received a primary vaccination series, a new study has found.
Investigators analyzed infection and vaccination data from a Danish national registry. The records included all people living in Denmark who tested positive for SARS-CoV-2 or who were vaccinated between January 2020 and January 2022. This group included more than 200,000 people who tested positive for the virus during each of the alpha, delta and omicron variant waves.
High protection levels
The results showed a high level of protection against recurrent infection. Previously infected people who had a primary vaccine series had up to 71% protection against reinfection during the alpha period, 94% during the delta period and 60% during the omicron period. The protection lasted up to nine months, reported Katrine Finderup Nielsen of the Statens Serum Institut in Denmark.
Longer follow-up times will be necessary to answer whether primary vaccination protects against severe outcomes, such as death and hospitalization, Nielsen and colleagues added.
Although protection appeared to be somewhat lower against reinfection with the omicron variant, the findings show that “previously infected individuals still benefit from COVID-19 vaccination across all three variant periods,” they wrote.
“[T]his shows the importance of vaccination also for those who might be protected by natural immunity,” Nielsen concluded.
Full findings were published in PLOS Medicine.
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