As the Omicron variant emerged in New York State, the number of people who have been infected with COVID for a second time has increased dramatically (“reinfection”). The Department of Health recently released a study with California and the CDC that looks at the occurrence of reinfection, among other trends. The Department will update reinfection data here on a weekly basis.
What is a reinfection?
A reinfection is when a person becomes infected with COVID, enough time passes, and later becomes infected again. A person is considered to have been reinfected if they test positive again 90 days or more after their first positive test.
How does this relate to other testing information DOH publishes?
Because data on reinfections and new infections are collected in different ways, they must be presented separately. The COVID-19 daily testing tracker and the positive tests over time dashboard show the number of first-time infections in New York State, based on when these new infections are reported to the State. The reinfection page presents the number of unique instances a person tested positive, thus including those who have tested positive again 90 days or more after their first positive test. To ensure each positive case is at least 90 days apart, reinfection cases are tracked by the date the sample was collected. Due to high volumes and differing reporting practices and timing, many testing sites do not report a case the same day the specimen is collected or the positive result is confirmed.
As a result, the total for any single day will differ between these two reports.
Reinfections and First Infections Over Time, By Region
This chart shows the weekly number of reinfections and their rate per 100,000 population.
*Grey shaded regions of figures and tables reflect recent weeks for which data are still accruing and estimates are subject to most change.
These data demonstrate low levels of reinfection, compared to first infections. This did not change after the Omicron variant emerged in December 2021, although the number of reinfections increased.
Data on this page also suggest that people with a prior diagnosed COVID-19 infection have had some protection against future infections. This is similar to lower levels of infection among vaccinated people (‘breakthrough infection’), compared to among unvaccinated people, which is used to demonstrate vaccine effectiveness.
Our in-depth study measured the relative protection afforded by vaccination and/or prior infection, during 2021, before the Omicron variant emerged. Both may offer protection against future infections and COVID-19 hospitalizations. However, because initial infections carry increased risk of illness and death, vaccination remains the safest strategy to prevent COVID-19 and associated complications and is the only strategy that should be pursued.
- New York data were matched in the Electronic Clinical Laboratory Reporting System (ECLRS) with the use of an exact matching process on the basis of first name, last name, and date of birth to find all instances of an individual’s positive test result.
- A positive result is to be deemed a repeat positive if it meets either of the following criteria:
- It has been 90 days since the first positive result for the person, regardless of whether or not the person had a positive test between the two results.
- It has been 90 days since the repeat positive result for the person, regardless of whether or not the person had a positive test between the two results.
- Both PCR and antigen laboratory tests are included in this analysis and are analyzed based on specimen collection date.
- Specimen lineage is currently not a factor of this report.
- Out of state residents are excluded.
- The COVID-19 testing tracker is updated daily with a 2:00 pm cutoff. This report is updated weekly and will cover the full ‘as of date’ time period. As such, the cumulative first infection total and most recent tested positive (cumulative) COVID-19 testing tracker day total will not align.
- All estimates in this report are preliminary and subject to change. In order to confirm that two positive tests were at least 90 days apart, the specimen collection dates must be evaluated, as opposed to the dates these cases were reported to NYS DOH. Because of this requirement and ongoing data submissions to ECLRS, it is expected that historical estimates may need minor changes as this report is updated to provide a timely snapshot of the epidemic.