So, what we really need is a study that looks at the degree to which people actually get re-infected, not more studies that look at antibodies. Once we have that, we can do a comparison with the results of the vaccine trials, and then we will finally have a reasonably good estimate of whether prior infection or vaccination provides a higher level of immunity, or if they are equivalent. That is now exactly what we have, thanks to a study that was recently published in The Lancet.
This was a cohort study carried out in the UK that recruited 25,661 NHS hospital workers and then followed them for an average seven months. The study was funded by the UK government. Participants were divided in to two cohorts, a covid positive cohort and a covid negative cohort. The purpose of the study was to see what proportion of people in each cohort went on to develop covid-19. The data were collected during the second half of 2020.
Everyone who had or had previously had a positive antibody test or PCR test for covid-19 at the beginning of the study was placed in to the covid positive cohort, and everyone else was placed in to the covid negative cohort. The covid positive cohort contained 8,278 participants at the beginning of the study, while the covid negative cohort contained 17,383.
Over the course of 2,047,113 days of follow-up in the covid positive group, there were 78 cases of symptomatic covid-19 (by which we mean a positive test + at least one symptom).
Over the course of 2,971,436 days of follow-up in the covid negative group, there were 1,369 cases of symptomatic covid-19.
This works out to a relative risk reduction 0f 92%. For comparison, the Pfizer vaccine trial reported a reduction of 95%, the Moderna trial reported an reduction of 94%, the Astra-Zeneca trial reported a reduction of 70%, and the Johnson&Johnson trial reported a reduction of 67%.
So, on the face of it, prior infection is equivalent to the Pfizer and Moderna vaccines in terms of the level of protection offered, and much better than the Astra-Zeneca vaccine and J&J vaccine. In light of this, it seems completely unnecessary for people who have had covid to get the vaccine. In fact, if the goal of governments is to get their populations to herd immunity as quickly as possible, it would make more sense to tell people who have had confirmed covid-19 that they don’t need to get vaccinated. Vaccinating people who have already had covid-19 means delaying vaccination of people who haven’t had it, which means delaying the onset of herd immunity.
But read it all.