NEW YORK (AP) — It may feel like you are surrounded by sniffles and coughs, but flu season activity is still low in many parts of the U.S.

New government data posted Friday shows that as of last week, flu activity was high in four states — Colorado, Louisiana, New Jersey and New York — and minimal or low in most others. Severity indicators are increasing but are still within the boundaries of a “mild” season, said officials at the U.S. Centers for Disease Control and Prevention.

A number of diseases tend to peak in the winter, thanks to indoor gatherings that help germs spread. The list includes not only colds and flu but also norovirus — a highly infectious cause of vomiting and diarrhea. Norovirus cases have generally been trending up in the last month.

Here are three seasonal respiratory viruses that experts are keeping an eye on:

Experts are closely watching flu

Last flu season was bad, with the overall flu hospitalization rate the highest since the H1N1 flu pandemic 15 years ago. With the addition of a late-reported case, child flu deaths reached 288, the worst recorded for regular U.S. flu season and the same number seen in the 2009-2010 flu pandemic.

This season's first pediatric flu death was reported this week.

There are reasons to fear this winter might be bad.

One type of flu virus — called A H3N2 — historically has caused the most hospitalizations and deaths in older people. So far this season, that's the type most frequently reported. Even more concerning, 89% of the H3N2 infections analyzed were a new version — known as the subclade K variant — that differs from the strain in this year’s flu shots.

Flu seasons often don't peak until around February, so it's too early to know how big a problem that mismatch will be.

The CDC recommends that everyone 6 months and older get an annual vaccination, and public health experts say it’s not too late. About 42% of U.S. adults and 41% of children have gotten flu shots this season, according to CDC data.

The shots may not prevent all symptoms but they can prevent many infections from becoming severe. That appears to be true for this year’s shot, according to a preliminary U.K. analysis.

RSV usually peaks soon

Respiratory syncytial virus is a common cause of cold-like symptoms. But it can be dangerous for infants and the elderly, and is known for filling hospitals with wheezing babies every fall and winter.

RSV seasons typically peak by December or January, but the season seems to be starting later than usual reported cases so far have been relatively low, according to the CDC.

It’s likely more RSV is coming, said Dr. Cameron Wolfe, an infectious diseases expert at Duke University, in an email. And, indeed, Friday’s CDC update showed signs that infections are increasing in the South and in mid-Atlantic states.

But relatively new vaccines may be helping. In 2023, the government licensed new RSV vaccines for pregnant women and older people, and injections of laboratory-made versions of antibodies for infants.

“Perhaps, glass half full, we’re cumulatively getting more people slowly vaccinated against RSV,” Wolfe said. “And because the virus mutates far less quickly than flu or COVID, the one vaccine you might have had as an older adult two or three years ago is likely still quite effective.”

As of October, about 41% of Americans 75 and older have been vaccinated, and about 40% of infants were reported to be protected, CDC data says.

The Trump administration, which has appointed vaccine skeptics to public health leadership and advisory positions, this week opened a review of the two injectable drugs used to protect babies and toddlers despite no signs of safety issues.

COVID-19 indicators are down from a summer peak

COVID-19 activity right now is relatively low.

This week, the CDC published research showing the COVID-19 vaccine can keep kids from developing a severe illness. Among children nine months to 4 years, the shots were 76% effective against symptoms severe enough to send a child to a hospital ER or urgent care center, the agency found. Among kids five to 17 years, it was 56% effective.

Other studies also found the shots are safe and effective for children. But the report comes out after Trump administration officials stopped recommending COVID-19 vaccines for healthy children, and as anti-vaccine advocates are petitioning the government to revoke licenses for the Moderna and Pfizer-BioNTech vaccines.

Few people are getting the shot this year. About 7% of children and 15% of adults have gotten this season's version of COVID-19 vaccine, according to the CDC.

In October, the agency stopped recommending COVID-19 shots for anyone, leaving the choice up to patients. Several doctors groups and scientific organizations argued against watering down vaccination recommendations for a disease that has been a primary or contributing factor in more than 1.2 million U.S. deaths.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.