The spread of the COVID-19 virus gets easier in winter as people increase their indoor activities, U.S. media outlet NPR reported on Friday citing early signs that could contribute to a possible new wave of infections in the country.

In northeastern parts of the U.S., such as Pennsylvania, Connecticut and Vermont, the levels of the virus being detected in wastewater are up, as indicated in a data tracker of the national wastewater surveillance program lead at the Centers for Disease Control and Prevention (CDC).

Infections and even hospitalizations have started rising in some of the same parts of New England, as well as some other northern areas, such as the Pacific Northwest, NPR reported citing Dr. David Rubin, the director of the PolicyLab at Children's Hospital of Philadelphia, which tracks the pandemic.

"We're seeing the northern rim of the country beginning to show some evidence of increasing transmission ... The winter resurgence is beginning," Rubin said.

More transmissible variant could emerge

U.S. top infectious disease expert Dr. Anthony Fauci urged Americans to stay cautious on the pandemic as there's always a "risk of an uptick" in winter, adding that "we shouldn't be surprised" if another new, more transmissible variant emerges, CNBC reported on Friday.

"We should anticipate that we very well may get another variant that would emerge, that would elude the immune response that we've gotten from infection and/or from vaccination," he said.

New research in August, published in The Lancet, found that some new variants – BA.4 and BA.5 subvariants – appear to evade immunity even more effectively than BA.5.

In the week ending October 8, the BA.4.6 subvariant is expected to make up 13.6 percent of total COVID cases in the U.S., higher than the 12.7 percent prevalence last week, CDC estimated on Friday.

The subvariant has been slowly increasing in prevalence across the U.S., despite BA.5 currently making up 79.2 percent of all cases circulating in the country.

According to the FDA's fact sheet, the BA.4.6 subvariant was likely to have a more than a 1,000-fold reduction in susceptibility to the antibody therapy, based on laboratory tests, Reuters reported on Saturday.