New York State Department of Health Study Shows Continued Effectiveness of COVID-19 Vaccines

Largest U.S. Study by Vaccine Type and Timing of Vaccination

Modest Declines in Vaccine Effectiveness for Infections May be Due More to Delta Variant and Behaviors Than Immunological Waning

Vaccine Effectiveness for Hospitalizations Remains High

ALBANY, N.Y. (October 11, 2021) – The New York State Department of Health today announced the release of a new study addressing one of the most critical questions regarding COVID-19 – the extent to which vaccine effectiveness is declining and whether these changes are due to waning immunity or other factors such as the predominance of the Delta variant.

The study, which expands upon the work of the Department's first-in-the-nation vaccine effectiveness study published by the Centers for Disease Control and Prevention (CDC) in August, concluded that declines in vaccine effectiveness (VE) for cases may have been driven primarily by the Delta variant or factors other than immunological waning, such as reduced use of masks. In contrast, VE for hospitalizations remained high, with modest declines limited to Pfizer-BioNTech and Moderna recipients 65 years of age and older. This finding supports targeted booster dosing recommendations.

"This latest study conducted by our renowned scientists here at DOH is the largest to examine in-depth changes in vaccine effectiveness over time broken down by all three COVID-19 vaccines types currently authorized for use in the United States," said senior author and Health Commissioner Dr. Howard Zucker. "It clearly demonstrates what we've been saying all along – getting a COVID-19 vaccine continues to be the best way out of this pandemic, and the best way for New Yorkers to prevent serious illness and hospitalization. We urge all New Yorkers to remain vigilant and get vaccinated against COVID-19 if you have not already done so."

DOH scientists expanded upon their earlier analytic approach, using statewide linked immunization, laboratory testing and hospitalization databases to calculate vaccine-effectiveness (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:


  • Between the weeks of May 1 and August 28, decreases in VE against laboratory-confirmed infections were greatest for Pfizer-BioNTech (-24.6% for 18-49, -19.1% for 50-64 and-14.1% for 65 and older), and similar for Moderna (-18.0% for 18-49, -11.6% for 50-64 and - 9.0% for 65 and older) and Janssen (-19.2% for 18-49, -10.8 for 50-64 and -10.9% for 65 years of age and older).


  • The declines in VE for laboratory-confirmed infections occurredsimultaneouslyacross groups defined by age, product and month of vaccination, during the weeks when Delta variant rapidly increased, with the largest declines seen for Pfizer-BioNTech recipients.
  • After the Delta variant exceeded 85% prevalence, these changes in VE plateaued, with more recently vaccinated people at higher protection levels in some groups. Modest continued declines in VE were seen for people 65 years of age and older.
  • These resultssuggest 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 for hospitalization for adults 18-64 years was 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 (95.0% to 89.2%) and Moderna (97.2% to 94.1%). VE was lower for Janssen, with no time trend, ranging 85.5%- 82.8%.
  • The study concluded that VE for COVID-19 hospitalizations remained high, with modest declineslimited to Pfizer-BioNTech and Moderna recipients 65 years of age and older.

Lead study author Dr. Eli Rosenberg of the Department of Health said, "The findings of our study support the need for boosters in older people in particular, and we encourage them to seek out a booster shot from their health care provider, pharmacy or mass vaccination site. We saw limited evidence of decline in effectiveness against severe disease for people ages 18 to 64 years old. While we did observe early declines in effectiveness against infections for this age group, this appears to have leveled off when the Delta variant became the predominant strain in New York. Together, this suggests that ongoing waning protection may be less of a current concern for adults younger than 65 years."

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

All New York State mass vaccination sites are opento eligible New Yorkers for walk-invaccinationon a first-come,first-serve basis.People who would prefer to schedule an appointment at a state-run massvaccinationsite can do so on the Am I Eligible App or by calling 1-833-NYS-4-VAX. People mayalso contacttheir local health department, pharmacy, doctor or hospital to schedule appointments where vaccines are available, or visit to find information onvaccineappointments near them.