Two-dose regimens of the Moderna and Pfizer-BioNTech mRNA vaccines provided a high level of protection against COVID-19 hospitalizations in a real-world evaluation at 21 U.S. hospitals during March–August 2021.
Vaccine effectiveness against COVID-19 hospitalization for Moderna and Pfizer-BioNTech vaccines was 93% and 88%, respectively, whereas the single-dose Janssen vaccine had somewhat lower vaccine effectiveness at 71%.
Persons vaccinated with Janssen vaccine also had lower postvaccination anti-SARS-CoV-2 antibody levels than did recipients of mRNA vaccines.
Although an immunologic correlate of protection has not been established for COVID-19 vaccines, antibody titers after infection and vaccination have been associated with protection.
These real-world data suggest that the 2-dose Moderna and Pfizer-BioNTech mRNA vaccine regimens provide more protection than does the 1-dose Janssen viral vector vaccine regimen.
Although the Janssen vaccine had lower observed effectiveness, 1 dose of Janssen vaccine still reduced risk for COVID-19–associated hospitalization by 71%.
Vaccine effectiveness against COVID-19 hospitalization was slightly lower for the 2-dose Pfizer-BioNTech vaccine than the Moderna vaccine, with this difference driven by a decline in vaccine effectiveness after 120 days for the Pfizer-BioNTech but not the Moderna vaccine.
The Moderna vaccine has also produced higher postvaccination anti-RBD antibody levels than did the Pfizer-BioNTech vaccine.
Differences in effectiveness between the Moderna and Pfizer-BioNTech vaccine might be due to higher mRNA content in the Moderna vaccine, differences in timing between doses ( 3 weeks for Pfizer-BioNTech versus 4 weeks for Moderna ), or possible differences between groups that received each vaccine that were not accounted for in the analysis.
The findings in this report are subject to at least six limitations.
First, this analysis did not consider children, immunocompromised adults, or vaccine effectiveness against COVID-19 that did not result in hospitalization.
Second, the confidence intervals for the Janssen vaccine effectiveness estimates were wide because of the relatively small number of patients who received this vaccine.
Third, follow-up time was limited to approximately 29 weeks since receipt of full vaccination, and further surveillance of vaccine effectiveness over time is warranted.
Fourth, although vaccine effectiveness estimates were adjusted for relevant potential confounders, residual confounding is possible.
Fifth, product-specific vaccine effectiveness by variant, including against Delta variants ( B.1.617.2 and AY sublineages ), was not evaluated.
Finally, antibody levels were measured at only a single time point 2–6 weeks after vaccination and changes in antibody response over time as well as cell-mediated immune responses were not assessed.
Two-dose series of the Moderna and Pfizer-BioNTech mRNA COVID-19 vaccines have provided high effectiveness for the prevention of COVID-19 hospitalizations during March–August 2021.
Protection for the Pfizer-BioNTech vaccine declined 4 months after vaccination.
A single dose of the Janssen viral vector vaccine had comparatively lower anti-SARS-CoV-2 antibody response and effectiveness against COVID-19 hospitalizations.
Understanding differences in effectiveness by vaccine product can guide individual choices and policy recommendations regarding vaccine boosters.
All FDA-approved or authorized COVID-19 vaccines provide substantial protection against COVID-19 hospitalization. ( Xagena )
Self WH et al, MMWR Morb Mortal Wkly Rep ePub: 17 September 2021