This article was originally published on HCPLive.
People previously infected with SARS-CoV-2 have a markedly reduced risk of re-infection – especially those who received a dose of Pfizer-BioNTech COVID-19 mRNA vaccine afterwards according to new results from a retrospective cohort study.
In new data presented by a team of investigators in Israel, SARS-CoV-2 re-infection appeared to be “relatively rare” among previously diagnosed patients; the risk was even less among those who received a dose of BNT162b2 (Comirnaty) ≥3 months after their infection.
The results of what investigators called the largest real-world observational assessment of natural versus vaccinated immunity to SARS-CoV-2 are limited by the conspicuous fact that it was performed before the spread of the highly transmissible Omicron variant. Nevertheless, they can help inform about policies and practices for vaccinating convalescent populations against the pandemic virus in the future.
Investigators led by Sivan Gazit, MD, MA, of the Kahn Sagol Maccabi Research & Innovation Center and Maccabitech Institute for Research and Innovation performed the retrospective cohort analysis to compare incidence rates of SARS-CoV-2 re-infection (per hazard). [HRs]) in previously infected unvaccinated individuals to those who received a single dose of the mRNA vaccine after infection.
As noted, current evidence supporting the combined effect of naturally acquired and vaccine-induced immunity to SARS-CoV-2 is insufficient – in particular to define the extent and shelf life of such immunity.
“Both short-term efficacy of the BNT162b2 mRNA COVID-19 vaccine and declining vaccine-induced immunity have been demonstrated, although the latter has been mild to severe disease,” investigators wrote. “In contrast to the large amount of published population-based research examining the long-term efficacy of COVID-19 vaccines, there is a relative lack of large studies examining the long-term protection against re-infection in previously infected individuals, although evidence suggests that long-term immunity has been declared. “
While previous trials have shown the effect of “hybrid immunity” against SARS-CoV-2, Gazit and colleagues noted that they include small cohorts and focus on biological outcomes, including antibody and memory B cell counts, rather than actual data. showing population-based results.
“Given the still unclear correlates of protection and the global need for vaccine resource allocation, there is a need for evidence of a significant booster effect for post-recovery vaccination from COVID-19,” they wrote.
The team used the Maccabi Health Services (MHS) database, which hosts the second largest health maintenance organization in Israel, to inform their analysis.
Investigators emulated 41 randomized controlled trials, including 107,413 MHS patients aged ≥16 years seeking SARS-CoV-2 outcome of infection, symptomatic disease, hospitalization, and death between March 2 and December 13, 2021.
Of the patients, 1374 had a positive PCR test result for SARS-CoV-2 reinfection, 874 experienced a symptomatic re-infection, and 10 contracted a COVID-19-related hospitalization after re-infection. Investigators observed no COVID-19-related deaths in their assessment. A further 21,131 patients received a second dose of the mRNA vaccine and were thus excluded from follow-up, and the remaining patients experienced no documented outcomes related to the virus.
Researchers observed an 82% reduced risk of re-infection among previously infected patients who received a single dose, compared with those previously infected with SARS-CoV-2 but unvaccinated (HR, 0.18; 95% CI, 0, 15 – 0.20). Symptomatic COVID-19 gene infection risk was reduced by 76% among patients with this “hybrid immunity” compared to those who were previously infected and unvaccinated (HR, 0.24; 95% CI, 0.29 – 0.29).
This finding supports previous small cohort studies that point to evidence of a boosting effect of neutralizing antibody activity or an anamnestic response in previously infected individuals receiving a single dose of an mRNA vaccine, as well as SARS-CoV-2-specific T- cell and memory B cell response and affinity maturation, “investigators wrote.
As Gazit and colleagues noted, the long-term effects of SARS-CoV-2 re-infection remain largely unknown. Even without contextual data from the period of Omicron variant outbreaks, the new large-scale results support the vaccine efficacy of single dose BNT162b2 given ≥3 months after a patient has first been infected with pandemic virus.
The study, “Prevalence of SARS-CoV-2 reinfection in individuals with naturally acquired immunity with and without subsequent administration of a single dose of BNT162b2 vaccine,”Was published online in Annals of Internal Medicine.