The Biden administration announced Wednesday that it is extending the nationwide mask requirement for public transit for 15 days as it monitors an uptick in COVID-19 cases.

There has been a slight increase in cases in recent weeks, driven by the BA.2 strain, with daily confirmed cases nationwide rising from about 25,000 per day to more than 30,000. Those figures are an undercount since many people now test positive on at-home tests that are not reported to public health agencies.

Severe illnesses and deaths tend to lag infections by several weeks. The CDC is awaiting indications of whether the increase in cases correlates to a rise in adverse outcomes before announcing a less restrictive mask policy for travel.