New cohort data from VA medical centers provide more evidence of a correlate between antibody levels and vaccine effectiveness for mRNA vaccines.
Investigators from the Centers for Disease Control and Prevention (CDC) have observed an approximate 10 percentage-point difference in efficacy between the 2 available COVID-19 mRNA vaccines after 4 months, according to new data from a military veteran cohort.
The findings, published in the CDC Morbidity and Mortality Weekly Report (MMWR), also showed a reduced mean antibody count in the observed older veteran patients underlying medical conditions than that in younger, healthier vaccine recipients—further stressing the need for continued COVID-19 vaccine monitoring and booster dose prioritization.
Led by Kristina L. Bajema, MD, of the CDC COVID-19 Response Team, investigators sought to compare the vaccine effectiveness of Moderna’s mRNA-1273 and Pfizer-BioNTech’s BNT162b2 at 2 different periods: 14-119 days and ≥120 days after receipt of the second vaccine dose. Their cohort included 1896 US veterans at 5 Veterans Affairs (VA) medical centers between February 1 and September 30, 2021.
Eligible patients for the test-negative case-control assessment were adults aged ≥18 years hospitalized at the VA medical centers; adults with COVID-19-like illness who received a positive SARS-CoV-2 nucleic acid amplification test result were included as case patients; those with COVID-19-like illness and a negative SARS-CoV-2 test results served as controls.
The trial cohort included 755 case patients and 1141 controls. A majority (92.7%) were male and approximately half (49.7%) were Black; another 8.5% were Hispanic. Median patient age was 67 years (IQR, 59 – 75).
With the Moderna vaccine, Bajema and colleagues observed an 89.6% vaccine efficacy at 14-119 days (95% CI, 80.1 – 94.5) and 86.1% efficacy at ≥120 days (95% CI, 77.7 – 91.3).
With the Pfizer-BioNTech vaccine, investigators observed 86.0% efficacy at 14-119 days (95% CI, 77.6 – 91.3) and 75.1% vaccine efficacy at ≥120 days (95% CI, 64.6 – 82.4).
In an assessment of antibody sera taken from 259 (40.6%) fully vaccinated controls, investigators observed greater anti-spike immunoglobulin G (IgG) levels at 14-119 days versus ≥120 days, irrespective of vaccine product. Younger vaccinated adults aged 18-64 reported greater mean anti-spike IgG levels than those aged ≥65 years.“These findings from a cohort of older, hospitalized veterans with high prevalences of underlying conditions suggest the importance of booster doses to help maintain long-term protection against severe COVID-19,” investigators wrote.
Previous research has shown correlations between binding antibody levels, neutralizing antibody levels, and COVID-19 vaccine efficacy in clinical trials—though no immune correlate of protection for COVID-19 vaccination has been established yet. Nonetheless, investigators noted changes in humoral immunity as they relate to real-world COVID-19 protection can be informed by pairing antibody levels from the same population in which COVID-19 vaccine effectiveness is investigated, as with this cohort assessment.
“Although this analysis was not powered to detect small differences in vaccine effectiveness by mRNA product as seen in other hospitalized settings, significantly higher post-Moderna vaccination antibody levels compared with Pfizer-BioNTech were observed, which is consistent with findings from other studies,” they concluded. “Potential reasons for this difference include higher antigen content and a longer interval between doses for the Moderna vaccine compared with the Pfizer-BioNTech vaccine.”