In a study yesterday in Clinical Infectious Diseases, Centers for Disease Control and Prevention (CDC) and Epic Systems researchers reveal that, among US adults at risk for severe COVID-19 in the Epic Cosmos database, the lowest rate of hospitalization was among those recorded as receiving three or more mRNA COVID vaccine doses plus Paxlovid (nirmatrelvir-ritonavir).
The researchers used electronic health data from April to August 2022 to calculate adjusted hazard ratios (aHRs) for hospitalization among outpatients who had mild to moderate confirmed COVID-19.
In total, 731,349 patients eligible for treatment with Paxlovid were included in the study, of whom 5,296 (0.72%) were hospitalized within 30 days of their COVID-19 diagnosis. Among the patients, 177,757 (24.3%) were unvaccinated, 157,011 (21.5%) received two doses of mRNA vaccines, 330,448 (45.2%) received three or more mRNA vaccine doses, and 66,133 (9.0%) were categorized in the "other vaccination" category.
Of unvaccinated patients, 20.2% received Paxlovid compared to 27.0% of patients who received two mRNA doses, and 33.0% of those who had received three or more mRNA vaccine doses.
The rate of hospitalization after receipt of Paxlovid was 19.7 per 100,000 person-days for those unvaccinated, 16.4 per 100,000 person-days for those with two mRNA vaccine doses, and 14.2 per 100,000 person-days for those with three or more mRNA vaccine doses.
78% reduction in hospitalization for most protected
The authors found a 78% reduction in risk of hospitalization among patients who had three doses of vaccine as well as Paxlovid (aHR, 0.22; 95% confidence interval [CI], 0.19 to 0.24.) Two vaccine doses and no Paxlovid was associated with an aHR of 0.74 (95% CI, 0.67 to 0.80), and three doses and no Paxlovid were linked to an aHR of 0.51 (95% CI, 0.47 to 0.55). Among unvaccinated patients who took Paxlovid, the aHR for hospitalization was 0.47 (95% CI, 0.40 to 0.55).
"Although we found evidence of substantial protection against hospitalization by nirmatrelvir-ritonavir, the absolute reduction in hospitalizations was modest," the authors concluded. "As an increasing proportion of the population has a degree of immunity from infection or vaccination and as pathogenicity has changed, overall hospitalization rates are lower than earlier in the pandemic."
Although we found evidence of substantial protection against hospitalization by nirmatrelvir-ritonavir, the absolute reduction in hospitalizations was modest.
The authors said Paxlovid still offers the greatest benefit to people at the highest risk of severe COVID-19 outcomes.
