Q: Are the mRNA COVID-19 vaccines more efficacious than COVID-19 viral vector vaccines or recombinant subunit vaccines?
A: The point estimates of vaccine efficacy for mRNA vaccines (Moderna and Pfizer-BioNTech), viral vector vaccines (Johnson & Johnson/Janssen and Oxford-AstraZeneca) and recombinant subunit vaccines (Novavax) are difficult to directly compare because the clinical trials for these vaccines were conducted at different times in different populations. Furthermore, the outcomes used to calculate the efficacy estimates differed between the studies.
Two systematic reviews/meta-analyses comparing relative effectiveness of different vaccine products did not find substantial differences in effectiveness by vaccine product (Rotshild, November 2021; Zhang, February 2023), and other observational studies have identified similar vaccine effectiveness estimates by vaccine product, without conducting direct statistical comparisons (Dos Santos, April 2023; Self, September 2021). One study in the U.S. found that mRNA vaccines had slightly higher effectiveness against hospitalization compared to the J&J/Janssen vaccine (Self, September 2021). However, these findings were conducted in a context that did not compare vaccine effectiveness estimates directly for measures of relative vaccine effectiveness.
When interpreting relative vaccine effectiveness measures (as compared to absolute vaccine effectiveness), it is important to remember that rVE measures depend both on the VE of the vaccine of interest and the VE of the comparison vaccine (Lewis, January 2023). This additional component of VE estimation can make rVE estimates challenging to interpret and may sometimes appear to minimize the impact of a vaccine with high absolute VE but low relative VE (if comparison vaccines also have high absolute VE).