Vaccination Against COVID-19 Reduces Hospitalization, Mortality Risk

Vaccinated individuals with breakthrough infection vs unvaccinated individuals with a reinfection are at a lower risk for hospitalization or death and lower risk of developing severe, critical, or fatal disease, according to study results published in The Journal of Infectious Diseases.

Researchers sourced data from the US Department of Veterans Affairs COVID-19 database to compare the incidence of breakthrough infections among vaccinated individuals with the incidence of reinfections among unvaccinated individuals, as well as assess the relative risk for severe or critical COVID-19 outcomes in these groups. Breakthrough infection was defined as the first confirmed COVID-19 infection more than 14 days after the last vaccine dose among those who had received at least 2 doses of an mRNA vaccine and had no previously confirmed COVID-19 infection. Reinfection was defined as the first confirmed COVID-19 infection more than 30 days after a confirmed prior infection in unvaccinated individuals. Severe or critical disease was defined as intensive care unit (ICU) admission, the need for mechanical ventilation, or death within 28 days of the initial diagnosis. The primary outcome was risk for hospitalization or death within 28 days of breakthrough infection or reinfection. Kaplan-Meier curves were used in statistical analysis.

A total of 13,976 matched pairs (median age, 56 years; men, 91%; White, 80%; median body mass index [BMI], 31.2 kg/m²; median Charlson comorbidity index, 1) were included in the analysis. Among vaccinated individuals, 49% and 51% received the BNT-162b2 and mRNA-1273 vaccines, respectively. The primary series was received by 39% of vaccinated individuals, while 61% had received at least 1 booster dose.

Among vaccinated individuals, 11.2% experienced breakthrough infections, of whom 11.8% were hospitalized or died within 28 days. Of unvaccinated individuals, 18.3% experienced reinfections, of whom 17.3% were hospitalized or died within 28 days.

The incidence rate per 1000 person-days of follow-up of breakthrough infection (0.30; 95% CI, 0.29-0.32) was similar to the incidence rate of reinfection (0.31; 95% CI, 0.30-0.32; P =.5); however, the incidence rate of hospitalization or death within 28 days was higher after reinfection (7.31; 95% CI, 6.66-8.03) vs breakthrough infection (4.69; 95% CI, 4.06-5.42; P <.0001).  

Incidence rates of hospitalization or death was higher after reinfection among those aged 65 and older and those with higher Charlson Comorbidity Index scores. Further, incident rates of hospitalization or death was higher after reinfection vs breakthrough infection among individuals with and without obesity.

Unvaccinated vs vaccinated individuals were more likely to experience hospitalization or death over a 28-day period after reinfection (P <.0001). Results were similar after stratifying by age, BMI, and Charlson Comorbidity Index score.

Study limitations include the observational nature of the data, potential exposure bias, and reduced generalizability of results to the national United States population.

“In conclusion, our results… reinforc[e] the critical role of vaccination in the management of COVID-19 at the population level,” the researchers concluded.

Disclosure: This research was supported by Merck Sharp & Dohme LLC. One study author reported affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

This article originally appeared on Infectious Disease Advisor