Comparative Effectiveness and Antibody Responses to Moderna and Pfizer-BioNTech COVID-19 Vaccines among Hospitalized Veterans - Five Veterans Affairs Medical Centers, United States, February 1-September 30, 2021

Abstract

The mRNA COVID-19 vaccines (Moderna and Pfizer-BioNTech) provide strong protection against severe COVID-19, including hospitalization, for at least several months after receipt of the second dose (1,2). However, studies examining immune responses and differences in protection against COVID-19-associated hospitalization in real-world settings, including by vaccine product, are limited. To understand how vaccine effectiveness (VE) might change with time, CDC and collaborators assessed the comparative effectiveness of Moderna and Pfizer-BioNTech vaccines in preventing COVID-19-associated hospitalization at two periods (14-119 days and ≥120 days) after receipt of the second vaccine dose among 1,896 U.S. veterans at five Veterans Affairs medical centers (VAMCs) during February 1-September 30, 2021. Among 234 U.S. veterans fully vaccinated with an mRNA COVID-19 vaccine and without evidence of current or prior SARS-CoV-2 infection, serum antibody levels (anti-spike immunoglobulin G [IgG] and anti-receptor binding domain [RBD] IgG) to SARS-CoV-2 were also compared. Adjusted VE 14-119 days following second Moderna vaccine dose was 89.6% (95% CI = 80.1%-94.5%) and after the second Pfizer-BioNTech dose was 86.0% (95% CI = 77.6%-91.3%); at ≥120 days VE was 86.1% (95% CI = 77.7%-91.3%) for Moderna and 75.1% (95% CI = 64.6%-82.4%) for Pfizer-BioNTech. Antibody levels were significantly higher among Moderna recipients than Pfizer-BioNTech recipients across all age groups and periods since vaccination; however, antibody levels among recipients of both products declined between 14-119 days and ≥120 days. 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.^†.

FIGURE

Serum anti-spike and anti-receptor binding domain immunoglobulin G levels after full vaccination among hospitalized veterans without current or previous SARS-CoV-2 infection — five Veterans Affairs medical centers, United States, February 1–September 30, 2021^⁋ Abbreviations: BAU = binding antibody units; IgG = immunoglobulin G; RBD = receptor binding domain. * Anti-spike and anti-RBD IgG levels were measured in sera of hospitalized veterans collected at or within 2 days of hospital admission. In these box and whisker plots, the central horizontal line of each box plot represents the median, with the box denoting the IQR and the whiskers representing 1.5 x IQR. ^† Excluded 25 controls with anti-nucleocapsid antibodies (>11.8 BAU/mL), suggesting a previous SARS-CoV-2 infection. ^§ The five Veterans Affairs medical centers are located in Atlanta, Georgia; the New York City borough of the Bronx; Houston, Texas; Los Angeles, California; and Palo Alto, California. ^¶ Serum specimens collected during March 22–August 31, 2021.