MANHATTAN — Two highly infectious variants of the coronavirus now account for more than half of new COVID-19 cases in the city, the de Blasio administration announced Wednesday.

"Unfortunately, we have found that the new variants of COVID-19 are continuing to spread," Dr. Jay Varma, Mayor Bill de Blasio's senior adviser for public health, said. "And when you combine the variant of concern, B.1.1.7, the one first reported in the U.K., and the variant of interest, B.1526 that was first reported here in New York —  together these new variants account for 51% of all cases we have in the city right now."

Health officials said that while they believe the New York strain is likely more infectious than older strains of the virus, they don't think that it results in more severe cases or reduces the effectiveness of the vaccines. 

Dr. Dave Chokshi, the city's health commissioner, said the New York strain is growing in prevalence across the five boroughs, with 39% of samples sequenced in the last week linked to that variant. 

"The variants have been detected in samples from across New York City, indeed in other states as well," Dr. Chokshi said. "That means we need all New Yorkers to pay attention to this."

The city said it is working with the Centers for Disease Control and other partners to continue analyzing the impact of the variants.

Officials emphasized that New Yorkers should continue doing what they've been doing: wearing masks, social distancing and getting tested for the virus.