mRNA COVID-19 vaccines 87% effective at preventing hospitalization amid delta surge
Among U.S. veterans at five Veterans Affairs medical centers, mRNA vaccines were about 87% effective at preventing COVID-19 hospitalizations amid the ongoing delta variant surge, according to data published by the CDC.
The researchers, who published their findings in the CDC’s Morbidity and Mortality Weekly Report, additionally concluded that the mRNA vaccines were 80% effective in preventing COVID-19-related hospitalization among adults aged 65 year and older, compared with 95% in those aged 18 to 64 years.
“COVID-19 mRNA vaccines (Pfizer-BioNTech and Moderna) have been shown to be highly protective against COVID-19–associated hospitalizations,” Kristina L. Bajema, MD, of the CDC COVID-19 Response Team, and colleagues wrote.
“Data are limited on the level of protection against hospitalization among disproportionately affected populations in the United States, particularly during periods in which the B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19, predominates,” they added. “U.S. veterans are older, more racially diverse and have higher prevalence of underlying medical conditions than persons in the general U.S. population.”
To analyze the effectiveness of mRNA vaccines against hospitalization for COVID-19 among U.S. veterans in the context of delta variant predominance, Bajema and colleagues conducted a test-negative case-control assessment of adults at five Veterans Affairs Medical Centers from Feb. 1 to Aug. 6. These centers were in Atlanta; the Bronx, New York; Houston; Los Angeles; and Palo Alto, California. Patient eligibility criteria included COVID-19-like illness and a molecular test for SARS-CoV-2 performed within 14 days prior to admission or during the first 72 hours of hospitalization.
Patients with COVID-19-like illness with a positive SARS-CoV-2 test result were included in the study as case-participants, while those with a negative test were included as controls. The researchers used electronic health records to review data on patients’ demographic characteristics, underlying medical conditions, presenting illness, SARS-CoV-2 test results, COVID-19 vaccination history and clinical course during hospitalization.
To assess vaccine effectiveness, the researchers used multivariable logistic regression to compare the odds for full vaccination between case-patients and controls, adjusting for medical center site, admission date, age, sex, race and ethnicity. Full vaccination was defined as receipt of both doses of an mRNA vaccine — either Pfizer-BioNTech or Moderna — at least 14 days before prior to taking the SARS-CoV-2 test.
In all, 1,175 participants — 388 case-patients and 787 controls — were included in the analysis. Among these patients, 93% were men, the median age was 68 years, 48.9% were Black, 40.4% were white, 7.9% were Hispanic of any race, and 44.4% had a Charlson comorbidity index score of three or greater. Overall, 13.9% of case-patients and 48% of the controls were fully vaccinated. Among the 171 case-patients with a determined SARS-CoV-2 lineage, delta was the predominant variant across all sites by July.
According to the researchers, the overall adjusted mRNA vaccine effectiveness against COVID-19 hospitalization was 86.8% (95% CI, 80.4% to 91.1%). In addition, vaccine effectiveness was similar both before and during the delta variant surge, with 84.1% for the period of February 1 to June 30, compared with 89.3% during July 1 to August 6. Vaccine effectiveness was 79.8% (95% CI, 67.7%-87.4%) among adults aged 65 years and older, and 95.1% (95% CI, 89.1%-97.8%) for those aged 18-64 years.
“This study among U.S. veterans hospitalized at five Veterans Affairs Medical Centers found that mRNA COVID-19 vaccines were highly effective for preventing COVID-19-related hospitalization, including during periods of widespread circulation of the delta variant,” Bajema told Healio Rheumatology. “These vaccines were effective against hospitalizations across all age groups, although lower among U.S. veterans aged 65 years and older.”
“These findings are reassuring as U.S. veterans in this assessment were older and more racially diverse,” Bajema added. “They also had a higher likelihood of underlying medical conditions, which places them at high risk for severe COVID-19 than the general U.S. population.”