A new study (not yet peer-reviewed) of over 50,000 employees of the healthcare system in Cleveland, Ohio, has found that previous infection provides very robust protection against re-infection and, importantly, that there is no gain to being vaccinated as well.
U.S. Senator Rand Paul tweeted the study’s conclusion: that it means vaccines should be prioritised for the not-previously-infected at home and abroad, not wasted on the already immune.
The confirmation of the protection provided by natural infection is very welcome, as is the finding that vaccinating the previously infected is superfluous. Given the significantly higher risk of adverse events for those previously infected (up to three times higher according to the ZOE Lancet study) and the world shortage of vaccines, there would seem to be a moral imperative to cease vaccinating the previously infected.
The study’s finding is particularly robust because of the large sample size and because there were zero instances of re-infection among the previously infected (both vaccinated and unvaccinated). This was despite the study period beginning at the peak of Ohio’s winter wave, so the unvaccinated had plenty of exposure to the virus. Other studies have found the relative risk reduction offered by previous infection to be 80% against all re-infection and 90% against symptomatic re-infection, so the results in this study were even higher than usually observed.
However, the study’s findings for vaccine effectiveness in the not-previously-infected are much less reliable.