New York

Study: Vaccine’s effectiveness declines, still effective at preventing serious illness

A dose of COVID vaccine is injected into a Schenectady woman's arm earlier this year.

A dose of COVID vaccine is injected into a Schenectady woman's arm earlier this year.

ALBANY — The state Department of Health on Wednesday released findings of a study that show COVID vaccines becoming less effective at preventing infection but still providing undiminished protection against severe illness.

New York’s first-of-its-kind study was published Wednesday by the federal Centers for Disease Control and was one of three studies that led the CDC to announce that it will recommend a third shot for anyone who received the two-shot Pfizer and Moderna vaccines. 

Similar guidance is likely to be issued for recipients of the single-shot Johnson & Johnson vaccine, when further data is accumulated.

The Food and Drug Administration will review the safety and effectiveness of the CDC’s proposed booster shot protocol, which calls for the third shot eight months after the second.

The federal government already has authorized booster shots for people who have weakened or deficient immune systems.

The DOH vaccine effectiveness study reviewed infections, hospitalizations and vaccination status among New Yorkers from May 3 through July 25.

Analysis showed that the three authorized COVID vaccines were 91.7% effective at protecting fully vaccinated people from so-called breakthrough infections in the week starting May 3 and 79.8% effective in the week starting July 19. Effectiveness fluctuated between 78.2% to 92.7% in the interim.

In that same period, the vaccines were 95.3% effective in both the first and last weeks at preventing infections serious enough to require hospitalization, fluctuating from 91.9% to 96.2% in the interim.

The study did not establish, and was not intended to establish, why the vaccine gradually became less effective at preventing infection in late spring and early summer.

But the study’s authors say there are three likely factors: People do not wear masks and keep distant from each other as much as they previously did; the Delta variant of COVID-19 spreads more easily; and the COVID vaccine, like other vaccines, becomes less effective over time in the human body.

The authors said it’s not known how much impact each of those three factors may have individually. That’s a determination for another study.

However, all three factors were clearly at play in New York from May 3 to July 25: Masking and social-distancing requirements eased sharply during that time; the Delta variant rose from 2% to 80% of new infections; and by the end of July, New Yorkers were as much as six months beyond their two doses of vaccine.

The study concludes that unvaccinated New Yorkers were eight times more likely to become infected with COVID-19 and 11 times more likely to be hospitalized because of it than those who were fully vaccinated.

The datasets include adults only. Most children are not eligible to receive the vaccine.

A similar phenomenon has been observed in Israel, which had one of the earliest and most effective COVID vaccination campaigns in the world: Fully vaccinated Israelis are now contracting the virus at an increasing rate.

The lead author of the study, Dr. Eli Rosenberg, said in a news release: “At this important time in the epidemic, we’ve observed a clear increase in cases for unvaccinated and even vaccinated people. Yet these results demonstrate that compared to unvaccinated people, those who are vaccinated remain consistently far more protected against infection and hospitalization. Vaccines remain a critical tool for COVID-19 prevention.”

Israel already has authorized booster shots for those over 50 years old.


New York state and individual counties provided statistical updates on the COVID-19 pandemic Wednesday:

  • On Tuesday, 322 COVID-positive patients were admitted to New York hospitals, bringing the patient census to 1,888; the census had been as low as 330 in early July. Capital Region hospitals climbed from 5 to 106 inpatients in that period.
  • On Tuesday, 4,737 new COVID infections were confirmed statewide, 251 of them in the Capital Region.
  • Twenty new COVID-related deaths were reported statewide Tuesday, including one each in Schenectady and Warren counties, bringing the official number of confirmed deaths in New York to 43,299.
  • Warren County has had a significant number of breakthrough infections; four elderly, fully vaccinated residents of a nursing facility that is battling an outbreak have died of COVID-19 in recent days.
  • Washington County reported that three of its 40 breakthrough cases resulted in hospitalization, the rest involved mild or no symptoms.
  • Saratoga County reported that 31% of new infections in the last seven days — a total of 105 — have been breakthrough cases. Three of the 173 county residents who have died of COVID had been fully vaccinated. 
  • Albany County reported 12 of the 25 county residents hospitalized Monday evening had been fully vaccinated, but said the severity of symptoms in those infected has decreased as the county’s vaccination rate rose.
  • Albany Medical Center, the region’s largest hospital, reported an increasing number of admitted patients who’d been vaccinated but contracted COVID anyway. It said their symptoms are on average milder, so much so that some are hospitalized not because of COVID but for other health concerns.

National reporting by The Associated Press was included in this story.

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