A large study of Covid following vaccination and booster, involving 1.6 million patients, has found surprisingly low incidence, especially in individuals younger than 65 years of age, with no high-risk conditions.
Hospitalisations for Covid-19 disease among individuals who had received vaccines and boosters occurred almost exclusively among high-risk patients including older adults and adults of all ages with certain comorbidities or immunocompromising conditions.
The retrospective study, published in the Journal of the American Medical Association (JAMA), found the incidence -- new cases over time -- of hospitalisation for Covid-19 pneumonia or death was 8.9 per 10,000 persons who had been vaccinated and boosted.
While the incidence for vaccinated and boosted older adults with comorbid or immunocompromising conditions was 10-fold higher, it was still a relatively low rate of occurrence of bad outcomes.
"This is remarkable, good news about the power and effectiveness of receiving Covid-19 boosting for all groups," said co-author and scientist Dawn Bravata from Regenstrief Institute and Roudebush VA Medical Center research.
"These results, from a period of Delta and Omicron predominance, should encourage people to get vaccinated and boosted," said Bravata, who is also a professor of medicine at Indiana University School of Medicine in the US.
To avoid misclassification of death or other serious outcomes due to Covid rather than to other health issues, the study authors rigorously evaluated patient medical records for breakthrough Covid-19, Covid-19 pneumonia and death, as opposed to simply considering all hospitalisations among patients with a positive Covid-19 lab test.
"Early in the pandemic, many researchers, including our own group, published studies about Covid-19 hospitalizations. But we're in a different era now when patients who are admitted to the hospital with a non-Covid illness are screened; some of whom will test positive. Evaluating outcomes such as Covid-19 pneumonia or mortality -- as opposed to simply considering all hospitalisation -- makes more sense," said Dr Bravata.
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