Study: Low rate of new COVID infections statewide among previously recovered

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ALBANY — A new study finds people who have had a previous COVID infection enjoy substantial protection against repeat infections.

It also quantifies the protection offered by vaccination, and concludes the vaccines are the best protective strategy.

While the first infection reduces the chances of a second infection, the first carries the risk of serious illness or death, and the possibility of transmitting the disease to other people who might face the same risks.

On Wednesday, the state Department of Health announced results of what it called the largest comparative study of its kind, performed in collaboration with the California Department of Public Health and the federal Centers for Disease Control and Prevention.

It mines electronic records to match the names and birth dates of more than 32 million adults who have had at least one laboratory COVID test, and it showed that previously infected people are being infected at a fraction of the rate of those who’d never been infected.

Reinfection is defined as a new infection more than 90 days after the first infection.

This gap narrowed significantly in late December and early January, amid the omicron surge, but the rate of reinfections still lags far behind the rate of first-time infections.

Statewide, the rate of reinfections was less than 1 per 100,000 residents for almost all of 2021, but it began to rise at the same time the rate of first-time infections jumped — early to mid-December, when the omicron variant began to race through New York. 

Data for the last three weeks is still being gathered but shows the reinfection rate peaking during the week starting Dec. 27, then beginning to decline.

In the eight-county Capital Region, first-time infections to date total 186,579, while reinfections total 4,393. The rates per 100,000 residents of first-time infections versus reinfections were as follows for the weeks starting on the given dates:

  • Dec. 6: 57, 1
  • Dec. 13: 67, 2
  • Dec. 20: 85, 4 
  • Dec. 27: 178, 11
  • Jan. 3: 239, 17
  • Jan. 10: 167, 11

In the six-county Mohawk Valley region, first-time infections to date total 92,74, while reinfections total 2,461. The rates per 100,000 residents of first-time infections versus reinfections were as follows for the weeks starting on the given dates:

  • Dec. 6: 74, 2
  • Dec. 13: 77, 3
  • Dec. 20: 77, 5
  • Dec. 27: 143, 10
  • Jan. 3: 205, 18
  • Jan. 10: 162, 14

The new study’s analysis of the protection vaccines offer is similar to a previous NYS DOH that showed vaccines, months after they are administered, provide diminished protection against infection, but retain most protection against symptoms serious enough to require hospitalization.  

The new study reported Wednesday placed people into four groups:

  • Unvaccinated, no prior infection
  • Fully vaccinated, no prior infection
  • Unvaccinated and recovered from a previous infection more than 90 days earlier
  • Fully vaccinated and recovered from a previous infection more than 90 days earlier

During the study period of May 30 to Nov. 20, 2021, new infections in Group 1 in New York were 4.5 times higher than Group 2, 14.7 times higher than Group 3 and 19.8 times higher than Group 4.

The study period does not include the omicron surge, and booster shots were not factored into the calculations.

Senior study author Eli Rosenberg of the NYS DOH said in a news release: “This analysis represents another chapter in our ongoing studies of this virus and the most effective ways to be protected from illness. Our knowledge evolves along with the virus and together with our public health partners, we will continue to study these issues in order to best inform and protect the public.”

Study co-author and acting state Health Commissioner Dr. Mary T. Bassett said: “Although the epidemiology of this virus may continue to change as new variants emerge, vaccination remains the safest way to prevent infection, hospitalization and death.”

DAILY UPDATE

Gov. Kathy Hochul on Wednesday said the state is showing continued progress against the winter surge. State Department of Health data reported Wednesday included:

  • 23,375 new lab confirmed infections statewide Tuesday, down from a recent one-day high of 90,132. The Capital Region accounted for 1,123 new infections and the Mohawk Valley 536.
  • A seven-day average positive test rate of 14.3% statewide, down from a recent peak of 22.5%. The Capital Region stood at 16.5% and the Mohawk Valley 16.0%.
  • A seven-day average daily case rate of 205 infections per 100,000 residents statewide, down from a recent peak of 382. The Capital Region stood at 179 and the Mohawk Valley 162.
  • 12,027 COVID-positive patients hospitalized statewide, down from a recent peak of 12,671 but up from a more recent low of 11,713. Capital Region hospitals are at an 11-month high of 430 COVID-positive patients; Mohawk Valley hospitals, with 160 such patients, are just shy of an 11-month high.
  • 165 COVID-related deaths were reported Tuesday in hospitals and elder-care facilities, including two each in Albany, Herkimer, Saratoga and Schenectady counties, and one each in Greene, Fulton and Washington counties.
By John Cropley

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