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Excerpts:
*Important notice
Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
By Dr. Chinta Sidharthan Oct 31 2022
Reviewed by Aimee Molineux
In a recent study posted to the Research Square* preprint server, a team of researchers from Italy investigated the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection and hospitalization among individuals with vaccinations and previous SARS-CoV-2 infections.
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About the study
The present research performed two case-control studies among COVID-19 patients registered at the Local Health Unit (LHU) in Vercelli, Italy, to estimate the efficacy of vaccination- and previous SARS-CoV-2 infection-induced immunity against infections and hospitalizations. The researchers also evaluated the effect of the SARS-CoV-2 Omicron variant on hybrid immunity and analyzed the efficacy of booster doses. The role of chronicity in SARS-CoV-2 infection and hospitalization risks was also assessed.
The analyzed data comprised demographic information on the patients registered at the LHU, swab-testing information, the dates and doses of vaccination administrations, hospital admission and discharge dates, the International Classification of Diseases, 9th revision (ICD-9-CM) code, drug provision information, and prescription charge exemptions for chronic diseases.
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Results
The results indicated that when vaccinations and previous infections were evaluated independently, vaccination reduced the risk of infections by 36% and the risk of hospitalization by 89%. Prior SARS-CoV-2 infections reduced reinfection and hospitalization risks by 65% and 90%, respectively. Vaccinated individuals with previous SARS-CoV-2 infections were at 62% and 98% lower risk of reinfections and hospitalizations, respectively.
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The Omicron variants had a significant effect in reducing the immunity induced by vaccinations and previous infections. After the emergence of the Omicron variant, the risk of disease among vaccinated individuals went from 43% to 67%. Unvaccinated, previously infected individuals exhibited a 45% reduction in reinfection risk after the Omicron variant’s emergence, compared to the 89% risk reduction seen before Omicron became prevalent. Individuals with vaccinations and previous infections also showed a decrease in protective effects against SARS-CoV-2 after the emergence of the Omicron variant (60% as compared to 79% before Omicron prevalence).
Conclusions
Overall, the results indicated hybrid immunity from completed primary vaccinations and previous SARS-CoV-2 infections significantly reduced reinfection and severity risks, even in individuals with chronic underlying health conditions.
The immune evasion by the Omicron variant resulted in a reduction in the protective effects of vaccination and previous infections. The efficacy of booster doses in increasing protection against infections and severe COVID-19 needs to be examined.
*Important notice
Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Written by
Chinta Sidharthan is a writer based in Bangalore, India. Her academic background is in evolutionary biology and genetics, and she has extensive experience in scientific research, teaching, science writing, and herpetology. Chinta holds a Ph.D. in evolutionary biology from the Indian Institute of Science and is passionate about science education, writing, animals, wildlife, and conservation. For her doctoral research, she explored the origins and diversification of blindsnakes in India, as a part of which she did extensive fieldwork in the jungles of southern India. She has received the Canadian Governor General’s bronze medal and Bangalore University gold medal for academic excellence and published her research in high-impact journals.
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