Large-Scale Study: Having COVID-19 Reduces Chances of Reinfection by 84%
A study published last week in The Lancet looked at staff of publicly funded hospitals in all regions of England. Participants were enrolled between June and December of last year.
After all the typical withdrawals and exclusions, the study included 25,661 participants. These poeople were assigned to two groups depending on whether they had a positive anti-body test and/or a previous positive PCR test (positive cohort) or not (negative cohort).
Participants were given PCR and antibody testing every two to four weeks. Because the study period overlapped the vaccine rollout in the UK, the study tracked and controlled for whether participants were vaccinated.
There were 8278 people in the positive cohort and they had 155 infections. There were 17,383 people in the negative cohort and they had 1704 infections.
Because participants were part of the study for varying lengths of time, you can't just compare the percentage infections directly. So the authors standardized by "person-days" to estimate an incidence density.
For the positive cohort (who had been previously infected) there were 7.6 reinfections per 100K person-days. For the negative cohort there were 57.3 infections per 100K person-days. The researchers estimate that this amounts to an 84% reduction in the risk of infection.
This is more good news that our immune systems can fight off SARS-CoV-2 once it learns what to look for. This is true whether it was taught by a previous infection, or by vaccination. A previous infection give almost, but not quite, as much protection as the best vaccines.
Image by Alexandra_Koch from Pixabay
