Natural immunity confers longer lasting and stronger protection against infection, symptomatic disease and hospitalisation caused by the Delta variant of SARS-CoV-2, compared to Pfizer-BioNTech two-dose vaccine-induced immunity.
The largest real-world analysis yet comparing natural immunity, gained from an earlier infection, to the protection provided by one of the most potent vaccines currently in use, showed that reinfections were much less common. The Israel research contrasts with earlier studies, which showed that immunisations offered better protection than an earlier infection, though those studies were not of the Delta variant.
The results are good news for patients who already successfully battled COVID-19, but show the challenge of relying exclusively on immunisations to move past the pandemic. People given both doses of the Pfizer-BioNTech vaccine were almost six-fold more likely to contract a Delta infection and seven-fold more likely to have symptomatic disease than those who recovered.
“This analysis demonstrated that natural immunity affords longer lasting and stronger protection against infection, symptomatic disease and hospitalisation due to the Delta variant,” the researchers said. The analysis also showed that protection from an earlier infection wanes with time. The risk of a vaccine-breakthrough Delta case was 13-fold higher than the risk of developing a second infection when the original illness occurred during January or February 2021: thatʼs significantly more than the risk for people who were ill earlier in the outbreak.
Giving a single shot of the vaccine to those who had been previously infected also appeared to boost their protection. The long-term benefit of a booster dose of the inoculation, which has just recently begun in Israel, is unknown.
The data was posted as a preprint article on medRxiv, and hasnʼt yet been reviewed.
Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections
Sivan Gazit, Roei Shlezinger, Galit Perez, Roni Lotan, Asaf Peretz, Amir Ben-Tov, Dani Cohen, Khitam Muhsen, Gabriel Chodick, Tal Patalon
Published in medRxiv on 25 August 2021
Background: Reports of waning vaccine-induced immunity against COVID-19 have begun to surface. With that, the comparable long-term protection conferred by previous infection with SARS-CoV-2 remains unclear.
Methods: We conducted a retrospective observational study comparing three groups: (1)SARS-CoV-2-naïve individuals who received a two-dose regimen of the BioNTech/Pfizer mRNA BNT162b2 vaccine, (2)previously infected individuals who have not been vaccinated, and (3)previously infected and single dose vaccinated individuals. Three multivariate logistic regression models were applied. In all models we evaluated four outcomes: SARS-CoV-2 infection, symptomatic disease, COVID-19-related hospitalisation and death. The follow-up period of June 1 to August 14, 2021, when the Delta variant was dominant in Israel.
Results: SARS-CoV-2-naïve vaccinees had a 13.06-fold (95% CI, 8.08 to 21.11) increased risk for breakthrough infection with the Delta variant compared to those previously infected, when the first event (infection or vaccination) occurred during January and February of 2021. The increased risk was significant (P<0.001) for symptomatic disease as well. When allowing the infection to occur at any time before vaccination (from March 2020 to February 2021), evidence of waning natural immunity was demonstrated, though SARS-CoV-2 naïve vaccinees had a 5.96-fold (95% CI, 4.85 to 7.33) increased risk for breakthrough infection and a 7.13-fold (95% CI, 5.51 to 9.21) increased risk for symptomatic disease. SARS-CoV-2-naïve vaccinees were also at a greater risk for COVID-19-related-hospitalisations compared to those that were previously infected.
Conclusions: This study demonstrated that natural immunity confers longer lasting and stronger protection against infection, symptomatic disease and hospitalisation caused by the Delta variant of SARS-CoV-2, compared to the BNT162b2 two-dose vaccine-induced immunity. Individuals who were both previously infected with SARS-CoV-2 and given a single dose of the vaccine gained additional protection against the Delta variant.
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