ALBANY, N.Y. (NEWS10)- As the rate of omicron rose in New York, so did the percentage of breakthrough cases. Both decreased immunity over time and the effectiveness of vaccines against omicron could be the driving factor for increased breakthrough cases.

On Dec. 6 the percentage of cases in those fully-vaccinated was 1.17%. By Dec. 27 it had reached 4.59% and on Jan. 1 it was up to 4.9% for New Yorkers 12+, according to the New York State Department of Health (DOH). Omicron was detected in 2.1% of COVID-19 cases tested on Dec. 4 but by Jan. 1 that had leaped to 96%.

“As predicted since it was first detected in New York in early December, the new omicron variant is moving swiftly through communities and is resulting in an uptick in cases for both unvaccinated and vaccinated people (breakthrough infections),” said DOH spokesperson, Erin Silk.

See the percentage of breakthrough cases grow as cases of omicron grew in December below:

Breakthrough cases

Dec. 61.17%
Dec. 131.33%
Dec. 202.09%
Dec. 274.59%
Source: DOH

Omicron cases

Dec. 141.9%
Dec. 1839.3%
Jan. 195.7%
Source: DOH

Percentages are a better indicator, rather than raw numbers because omicron is so widespread. Raw numbers indicate samples that were taken to date and the number of them confirmed to be from omicron, the DOH said.

 “While it is the case that 4.59% of all vaccinated people have had a breakthrough infection to date, our week-by-week comparison shows that levels of infection are higher among those unvaccinated, with the unvaccinated experiencing infections at about 4.5 times the rate as those vaccinated,” Silk said.

The overall effectiveness of the vaccines has changed only slightly from 81% on Dec. 6 to 78% on Dec. 27 in the 18+ population in the state. Hospitalizations for breakthrough cases are up but the percentage remains less than 1% at .15%.

“Vaccination, and getting boosted if eligible, remains the best way for New Yorkers to increase their protection from infection, and to lessen severity if they contract the virus,” said Silk.

As the use of at-home testing has become more popular some counties like Albany and Warren have given residents a way to report results. At-home test results are not being tracked by the DOH. Laboratories are required to report all molecular, antigen, and serological tests to the state, according to the DOH.