There have also been reports that cases of invasive infections of group A Streptococcus bacteria, or strep A, may be on the rise in the United States and Europe. Although these cases remain rare, they may be related to the recent surges in flu and R.S.V., which can leave people more vulnerable to invasive strep, officials have said.
However, some encouraging signs have recently emerged, especially regarding R.S.V. Nationally, hospitalization rates and R.S.V. detections have fallen since mid-November, according to C.D.C. data.
“I think it’s likely that the R.S.V. season has peaked in most parts of the country,” Dr. Pitzer said. “I think that there is a light at the end of the tunnel.”
The trajectory of the flu surge is more difficult to discern, scientists said. Levels of the virus are still very high, and some locations may be seeing their flu peaks now. “It still looks really serious most everywhere,” Dr. Lover said.
But there are hints that conditions may be beginning to improve in some areas of the country, including in parts of the South and the Mid-Atlantic States. According to the C.D.C.’s latest influenza report, during the week that ended on Dec. 10, the percentage of laboratory samples testing positive for flu held steady, nationally, and the number of hospital admissions declined, compared with that of the previous week.
Several experts expressed hope that this year’s early-starting flu season might also end early, with cases plummeting quickly as the virus finds fewer people to infect. “It burns through all the people who are susceptible to disease or to infection and doesn’t have as much fuel during the traditional season,” said Justin Lessler, an infectious disease epidemiologist at the University of North Carolina at Chapel Hill.
Earlier this year, for instance, Australia saw a severe, early flu season, with cases rising precipitously and then “crashing down pretty quickly,” Dr. Shaman noted.
