Third COVID vaccine dose boosts effectiveness against hospitalizationA third COVID-19 vaccine dose increased vaccine effectiveness (VE) against hospitalization from 82% to 97% among adults with healthy immune systems and from 69% to 88% among those with impaired immunity, according to a study today in Morbidity and Mortality Weekly Report (MMWR).Led by researchers from the Centers for Disease Control and Prevention (CDC) COVID-19 Emergency Response Team, the study involved 1,385 COVID-19 patients and 1,567 uninfected controls admitted to 21 US hospitals from Aug 19 to Dec 15, 2021.
The study period encompassed the emergence and eventual dominance of the highly transmissible Delta (B1617.2) variant.The researchers estimated the VE of a third dose of the Pfizer/BioNTech and Moderna mRNA vaccines against COVID-related hospitalization in 312 adults who received a third shot at least 7 days before symptom onset, relative to 1,251 adults who hadn't received a third dose.
They estimated VE using logistic regression, comparing the chances of being vaccinated versus unvaccinated among COVID-19 patients and controls.
Median patient age was 62 years, 49% were women, and 58% were White.Of 1,875 participants with uncompromised immune systems, 57% were unvaccinated against COVID-19, 36% had received two doses of vaccine, and 7% had been given a third dose.