Here is my response to the following claim:
Okay, yes, I concede that natural immunity is superior to vaccine immunity, but perhaps still vaccinating the Covid-recovered anyway might just improve their immunity a bit more.
The largest population-based study comparing natural immunity and vaccine immunity (a study I will summarize in more detail in my next Research Overview post) actually analyzed this situation: giving a one-dose Pfizer vaccine booster to those previously infected and comparing these individuals to unvaccinated previously infected individuals. The previously infected went from 99.74% immunity before vaccination to 99.86% after vaccination for the duration of the study.
The differences here before and after vaccination are clearly negligible and have no clinical relevance whatsoever. This minuscule, barely perceptible bump in immunity actually included asymptomatic reinfections. The same analysis for symptomatic reinfections found no statistically significant differences at all. When the efficacy of natural immunity is already extremely high, vaccination—or other interventions for that matter—cannot improve it much.
On the other hand, vaccination always involves some risk of adverse events, however small. Such risks are warranted only where there are potentially meaningful clinical benefits. In fact, as I will summarize in a future Research Overview post, several studies now suggest that individuals with prior Covid infections are at higher risk of vaccine adverse effects compared to those without a history of Covid infection.
To make this very concrete, consider the number needed to treat (NNT) to prevent one asymptomatic reinfection in those with natural immunity vs. the number needed to harm (NNH) by causing a vaccine adverse event. We would need to vaccinate 833 Covid-recovered people to prevent 1 asymptomatic reinfection (NNT=833). We cannot even calculate the number of necessary vaccinations to prevent 1 symptomatic infection because the data shows no differences before and after vaccination for symptomatic infections, hospitalizations, or deaths.
According to data from the U.K. looking at vaccination for previously infected, the number needed to cause an additional clinically significant vaccine adverse event was 11 (NNH=11), with the most common adverse events being fever, fatigue, myalgia-arthralgia and lymphadenopathy. In short: to prevent one case of asymptomatic reinfection, we would cause over 75 cases of clinically significant adverse events (NNT/NNH = 833/11). The number of people harmed to prevent one case of symptomatic reinfection would be even higher—too high to calculate with our current data.
The risk/benefit tradeoff just does not make sense. This is one clinical reason why mandating vaccination for Covid recovered individuals is ethically unjustifiable and medically likely harmful.
Link to Israeli study: https://www.medrxiv.org/content/10.1101/2021.08.24.21262415v1.full.pdf