New York State Department of Health Announces Publication of Study on COVID-19 Vaccine Effectiveness in New England Journal of Medicine

Largest U.S. Study by Vaccine Type and Timing of Vaccination Shows Continued Effectiveness of COVID-19 Vaccines

ALBANY, N.Y. (December 01, 2021) – The New York State Department of Health today announced that its latest study on vaccine effectiveness has been published in the New England Journal of Medicine. In October, an early version of the study was released on medRxiv and expanded upon the Department'sfirst-in-the-nation vaccine effectiveness study published by the Centers for Disease Control and Prevention (CDC) in August. In the final, peer-reviewed study published in the December 1 issue of the New England Journal of Medicine, DOH researchers conclude that vaccine effectiveness against hospitalizations remains high and that modest declines in vaccine effectiveness (VE) against infections may be due more to the Delta variant and declining preventive behaviors, like mask wearing, than waning immunity after vaccination.

Although protection against hospitalizations stayed high, the study found modest declines limited to Pfizer-BioNTech and Moderna recipients 65 years of age and older. This finding supports focusing booster doses on this group at higher risk for hospitalization.

Lead study author Dr. Eli Rosenberg of the Department of Health said, "This latest study conducted by DOH scientists found declines in vaccine effectiveness against infection may have been primarily driven by factors other than waning immunity. At the direction of former Health Commissioner Dr. Howard Zucker, DOH researchers began this groundbreaking study, and we look forward to further studying the best ways to protect the public from COVID-19 under Dr. Mary Bassett's leadership."

Deputy Commissioner for Public Health Dr. Ursula Bauer said, "This study examines the real-world effectiveness of COVID-19 vaccines over time and gives researchers and policymakers further evidence that vaccines are one of the most effective tools in our fight against this unprecedented pandemic. Simply put, COVID-19 vaccines work and work well. Combining preventive behaviors such as masking and physical distancing, along with vaccination, is the best strategy to contain this pandemic."

DOH scientists expanded upon their earlier analytic approach, using statewide linked immunization, laboratory testing and hospitalization databases to calculate VE over time. The new study of nearly nine million New Yorkers 18 years of age and older analyzed changes in VE by age, vaccine product and month of vaccination. The study looked at people vaccinated in January through April 2021 and examined their levels of new diagnosed infections and hospitalizations from May to August 2021, compared to people who never received a vaccine.

The analysis found the following:


  • During the week of May 1, across age groups and the 3 FDA-authorized vaccines (produced by Pfizer-BioNTech, Moderna, and Janssen), the median VE against laboratory-confirmed infections was 93.4% (range, 77.8 to 98.0). This declined to a low point of 73.5% (range, 13.8 to 90.0) around July 10, when the prevalence of the delta variant was 85.3%. By the week of August 28, when the prevalence of the delta variant was 99.6%, the effectiveness was 74.2% (range, 63.4 to 86.8).


  • The declines in VE for laboratory-confirmed infections occurred simultaneously across groups defined by age, product and month of vaccination, during the weeks when the Delta variant rapidly increased, with the largest declines seen for Pfizer-BioNTech recipients.
  • These results suggest that after the Delta variant exceeded 85% prevalence, these declines changes in VE plateaued, with more recently vaccinated people at higher protection levels in some groups. Modest continued declines in VE were observed among people 65 years of age and older.
  • These results suggest that declines in VE for infections occurred during the study time period but may have been driven primarily by factors other than immunological waning, such as the Delta variant or changes in COVID-19 prevention behaviors.


  • Vaccine effectiveness against hospitalization for adults 18-64 years was nearly consistently more than 86% across cohorts, with no trend over time. Among people aged 65 years or older, VE declined from May to August for Pfizer-BioNTech (94.8% to 88.6%) and Moderna (97.1% to 93.7). VE was lower for Janssen, with no time trend, ranging 80.0%- 90.6%.
  • The study concluded that VE against COVID-19 hospitalizations remained high, with modest declines limited to Pfizer-BioNTech and Moderna recipients 65 years of age and older.

More information about the Department's study is available here.