People who have previously recovered from COVID-19 have been observed to have better protection against the Delta variant of the CCP virus compared to those who received the Pfizer–BioNTech vaccine, according to a study from Israel.
“This analysis demonstrated that natural immunity affords longer-lasting and stronger protection against infection, symptomatic disease, and hospitalization due to the Delta variant,” researchers from Maccabi Healthcare and Tel Aviv University said.
“This is the largest real-world observational study comparing natural immunity, gained through previous SARS-CoV-2 infection, to vaccine-induced immunity, afforded by the BNT162b2 mRNA vaccine.”
Natural immunity refers to the immunity a person retains after having recovered from a virus, in this case, the CCP virus, also known as the novel coronavirus.
A preprint of the study, which is yet to be peer-reviewed, was published on medRxiv on Aug. 25.
Researchers used data from Maccabi Healthcare Services, Israel’s second-largest health fund, between March 1, 2020, and Aug. 14, 2021. They conducted statistical analysis on those eligible for three study groups: people who received two doses of the Pfizer vaccine; those unvaccinated who were previously infected with COVID-19; and those who were previously infected and later received one dose of the vaccine.
The outcomes were observed for the period between June 1 and Aug. 14, 2021, which corresponds to the time the contagious Delta variant became the dominant CCP virus strain in Israel.
Researchers found that people fully vaccinated with the Pfizer vaccine were 13.06 times more likely to contract the Delta variant of the CCP virus and 27.02 times more at risk of symptomatic disease compared to those who had recovered from a previous infection of COVID-19. The figures apply when comparing cases where the first vaccination or infection occurred between January and February 2021.
When researchers compared cases of prior infection that occurred between March 2020 and February 2021 with vaccinations between January and February 2021, they found that the vaccinated cohort was 5.96 times more likely to contract the Delta variant and 7.13 times more at risk for symptomatic disease compared to those previously infected.
The results suggest that natural immunity gained from having survived a previous infection of COVID-19 may wane over time against the Delta variant, the authors wrote.
Those vaccinated were at a greater risk of COVID-19-related hospitalizations compared to those who were previously infected, the authors noted. They said that being 60 years of age or older increased the risk of infection and hospitalization.
In another analysis, the authors compared previously infected people with those who were previously infected and also had one dose of the vaccine. They found that the group with one vaccine dose was marginally, or 0.53 times, less likely to be reinfected with the Delta variant.
The authors said the results suggest that previously infected people “seem to gain additional protection from a subsequent single-dose vaccine regimen,” but they “could not demonstrate significance” in the cohort.
They acknowledged a number of limitations, including that the study only observed the protection of the vaccine or natural immunity against the Delta variant. The study furthermore only observed the protection of the Pfizer vaccine and didn’t look at other vaccines or the effects of a third dose, or booster, of the Pfizer vaccine.
They also noted that because COVID-19 testing such as PCR was not required to be performed by protocol in Israel, the true number of asymptomatic infections may have been under-represented in the study, because such individuals often don’t go to get tested.
The study authors also acknowledged that certain health behaviors such as social distancing and the wearing of masks may play a confounding role in the study.
Since the Delta variant began to spread starting around June, the Israeli health ministry twice reported a drop in the vaccine’s efficacy against infection—in early and late July—as well as a slight decrease in its protection against severe disease.
Scientists and agencies continue to probe whether a third dose is necessary. The country on Aug. 24 has expanded the age of eligibility for a third dose of the Pfizer vaccine to those over 30 years old.
Amid the ongoing spread of the Delta variant, Israel has reimposed indoor mask-wearing, limitations on gatherings, and ramped-up rapid testing, as well as reinstated its “Green Pass” COVID-19 vaccine passport program in late July.