Primary end points were post-index diagnostic nucleic acid amplification test (NAAT results), with infection defined as a positive diagnostic test post-index, measured in 30-day intervals (0-30, 31-60, 61-90, >90 days).
The study concluded:
- Patients with positive antibody test results (IgG) were initially more likely to have positive NAAT results, consistent with prolonged RNA shedding
- The positive-antibody patients became markedly less likely to have positive NAAT results over time, suggesting that seropositivity is associated with protection from infection (the duration of protection is unknown, and protection may wane over time).
- These results indicate that seropositive individuals were more likely to have had symptoms of and/or a diagnosis of COVID-19 than seronegative individuals (although the majority of subjects in both groups lacked evidence of prior infection in the observable data)
- The degree of protection (10-fold) associated with seropositivity appears to be comparable to that observed in the initial reports of the efficacy of mRNA vaccines in large clinical trials1,2,3
- Protection induced by a vaccine is clearly preferable, as the population-wide risk of a serious outcome from an authorized or approved vaccine is expected to be orders of magnitude lower than that from natural infection