ALBANY, N.Y. (NEWS10) – The New York State Department of Health (NYSDOH) has published a comparative study on immunity to COVID-19 from vaccines and its effectiveness. Researchers found that from May to November 2021, COVID-19 cases and related hospitalization were substantially lower among those who had been vaccinated and/or survived a previous infection.

According to researchers, the study concluded that although the Delta variant emerged, new infections and hospitalizations were lowest among people with prior infectionespecially those who were also vaccinated. They say continued research on vaccine effectiveness results show vaccination remains the safest way to prevent future COVID-19 infections and severe outcomes, including death. 

Since the beginning of the pandemic, more than 63,500 New Yorkers have died from COVID-19. Researchers say It found that both vaccination and a prior infection provided protection against future infection and hospitalization.

The NYSDOH study also contains new data on reinfections, which was conducted in collaboration with researchers from the California Department of Public Health and the Centers for Disease Control and Prevention and published in the CDC’s Morbidity and Mortality Weekly Report.

The study is based on over 32 million adults who had at least one COVD-19 test, grouped as follows: 

  • Group 1 – Unvaccinated with no previous laboratory-confirmed COVID-19 diagnosis
  • Group 2 – Vaccinated (14 days after completion of a primary COVID-19 vaccination series) with no previous COVID-19 diagnosis
  • Group 3 – Unvaccinated who survived a previous COVID-19 diagnosis
  • Group 4 – Vaccinated who survived a previous COVID-19 diagnosis

During the study period of May 30 through November 20, 2021, new COVID-19 cases in both states were highest among unvaccinated people without a previous COVID-19 diagnosis compared with the other three groups. Researchers noted that after the Delta variant became prominent in late June and July, case rates were lower among those vaccinated with no previous COVID-19 diagnosis. The lowest they say among the two groups with a previous COVID-19 diagnosis.

For example, In New York State beginning the week of October 3, unvaccinated people without a previous COVID-19 diagnosis were 4.5 fold more likely to have a positive COVID-19 test than vaccinated people without a previous COVID-19 diagnosis. Group 1 vs. 2 was 14.7-fold more likely than unvaccinated people with a previous diagnosis, and Group 1 vs. 3, had a 19.8-fold more likely than vaccinated people with a previous COVID-19 diagnosis in Group 1 vs. 4.

During the same period, compared with unvaccinated people without a previous COVID-19 diagnosis, numbers and hospitalization rates in California followed a similar pattern from the study conducted. Researchers added these results, in two large states like California and New York comprised one-in-six U.S. deaths from COVID-19 through the end of November.

Researchers say it suggests that vaccination protected against infection and related hospitalization, along with surviving a previous infection protected against reinfection and hospitalization. These findings apply to the period before the emergence of the Omicron variant and the widespread use of booster doses they say.

To provide ongoing information on reinfections to the public, the NYSDOH has also launched a new dashboard with data on COVID-19 reinfection in New York State. The Department similarly launched a pioneering dashboard on breakthrough data after the publication of its study on vaccine effectiveness last year.