Hybrid COVID-19 immunity offers higher protection than previous infection alone
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People who are vaccinated and have previously been infected with COVID-19 had a 97% reduced chance of severe COVID-19 infection 1 year after their last vaccination or infection, researchers determined.
“The landscape of population immunity has become more complex over time. There are good estimates about the level protection provided by COVID-19 vaccination. However, many people with vaccinations have also had an infection,” Niklas Bobrovitz, DPhil, MD Program student at the University of Toronto’s Temerty Faculty of Medicine, told Healio.
“We wanted to better understand protection for people with vaccination and a previous infection, called hybrid immunity, to help inform vaccine policy," Bobrovitz said.
Bobrovitz and colleagues performed a systematic review and meta-regression during which they searched for cohort, cross-sectional and case-control studies in MEDLINE, Embase and Web of Science, among other large databases, from Jan. 1, 2020, through June 1, 2022, using keywords related to SARS-CoV-2, reinfection, protective effectiveness, previous infection, presence of antibodies and hybrid immunity.
According to the study, the main outcomes were the protective effectiveness against reinfection and hospital admission or severe disease of hybrid immunity, hybrid immunity relative to previous infection alone, hybrid immunity relative to previous vaccination alone and hybrid immunity relative to hybrid immunity with fewer vaccine doses.
In total, 11 studies reporting the protective effectiveness of previous SARS-CoV-2 infection and 15 studies reporting the protective effectiveness of hybrid immunity were included in the final analysis. For hybrid immunity, there were 153 estimates available.
The researchers determined that the effectiveness of hybrid immunity against hospital admission or severe disease was 97.4% (95% CI, 91.4%-99.2%) at 12 months with a primary vaccination series and 95.3% (95% CI, 81.9%-98.9%) at 6 months with the first booster vaccination after the most recent infection or vaccination.
They also found that the effectiveness of hybrid immunity following primary series vaccination against reinfection waned to 41.8% (95% CI, 31.5%-52.8%) at 12 months, the effectiveness of hybrid immunity following first booster vaccination waned to 46.5% (95% CI, 36%-57.3%) at 6 months.
For previous infection alone, there were 97 estimates, based on which the researchers found that effectiveness of previous infection against hospital admission or severe disease was 74.6% (95% CI, 63.1%-83.5%) at 12 months, whereas the effectiveness of previous infection against reinfection waned to 24.7% (95% CI, 16.4%-35.5%) at 12 months.
Based on these findings, Bobrovitz said that there is “significant benefit” to getting vaccinated even after previous COVID-19 infection and that periodic booster vaccinations will help maintain protection against severe disease and future infections.
Bobrovitz added that people should not deliberately get infected by COVID-19 to get hybrid immunity.
“You could die, get hospitalized, suffer from long COVID, or transmit the virus to a vulnerable person,” Bobrovitz said. “If you have been lucky enough not to get infected so far, continue to follow public health guidance and get the vaccinations for which you are eligible.”
In a related commentary published in The Lancet Infectious Diseases, Viviane S. Boaventura, MD, PhD, of the LIB and LEITV Laboratories at the Instituto Gonçalo Moniz, and colleagues wrote that after the first 2 years of massive vaccination campaigns worldwide and almost a full year of omicron subvariants causing high rates of infection worldwide, the focus of first-generation vaccines should be prevention of severe disease.
“We are currently facing a new wave of omicron subvariants. While waiting for data about the effectiveness of bivalent and other next-generation vaccines, the gold standards against COVID-19 remain both nonpharmacological strategies to prevent SARS-CoV-2 infection and vaccination to avoid severe disease," Boaventura wrote.
References:
- Boaventura VS, et al. Lancet Infect Dis. 2023;doi:10.1016/S1473-3099(22)00880-5.
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Bobrovitz, N. et al. Lancet Infect Dis. 2023;doi: 10.1016/S1473-3099(22)00801-5.
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