Vaccinations remain a solid guard COVID-19 related hospitalizations and have not dramatically reduced in effectiveness, a study released on Monday by the state Department of Health found.

At the same time, the study bolstered support for providing booster shots to people 65 and older given modest declines in recipients of the Pfizer and Moderna vaccinations.

The study assessed nine million New Yorkers 18 years and older and analyzed vaccine effectiveness by age, reviewing people who received shots between January and April of this year. The study also examined levels of newly diagnosed infections and hospitalizations from May to August of this year, compared to people who never received the vaccine.

While vaccination effectiveness has dropped across age groups, the rise in cases came during the weeks of the spread of the highly contagious delta variant. Once the delta variant exceeded 85% prevalence in New York, changes in vaccine effectiveness plateaued as people who were more recently vaccinated showed higher levels of protection in some groups.

Researchers at the state Department of Health believe these drops in vaccine effectiveness for infections during the study's time period may have been driven by the spread of delta or changes in prevention behaviors, such as a decrease in mask wearing, and not immunological waning.

And among hospitalizations vaccine effectiveness for adults between the ages of 18 and 64 remained 86% with no decrease over time. Among people age 65 and older, vaccine effectiveness dropped from May to August from 95% to 89% for Pfizer recipients, and from 97% to 94% for those who received the Moderna vaccine.

“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," said Eli Rosenberg, the lead author of the study. "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.”

New York has made vaccine booster shots available to those who qualify, including people age 65 and older as well as people who work in sectors of the economy that may put them at an increased risk of contracting the virus.