Summer heat, outdoor fun… and cold symptoms?

These three elements may not be related in many people’s minds, partly due to common myths about germs and partly because many  viruses  actually have lower activity levels in the  summer.

But it is possible to have a runny nose, or worse, in the summer. Federal data released Friday, for example, shows that  COVID-19  is on the rise in most  U.S. states , with an increase in emergency room visits among people of all ages.

Here’s what you need to know about summer viruses.

To what extent are colds and the flu circulating at this time?

The number of people seeking medical care for three key illnesses — COVID-19, influenza, and respiratory syncytial virus, or RSV — is currently very low, according to data from the  Centers for Disease Control and Prevention.

Flu cases are declining and RSV  has remained stable. But COVID-19 is on the rise in most U.S. states. “Moderate” COVID-19 activity is estimated based on wastewater data from across the country.

Wastewater samples studied by the CDC also show that the  XFG variant, nicknamed stratus,  is the most common in the United States. Stratus can cause a “razor-like” throat pain and is considered a “variant under surveillance” by the World Health Organization. The WHO said the variant is only marginally better at evading  people’s immune systems  and that vaccines still work against it.

COVID-19 is expected to stabilize into a winter seasonal pattern like other  coronaviruses , but in recent years there has been a surge in late summer, said Dr. Dean Blumberg, chief of pediatric infectious diseases at the University of California, Davis Children’s Hospital.

Other viruses that circulate at this time of year include the one that causes ” hand, foot and mouth disease ,”  which has cold-like symptoms as well as sores and rashes, and  norovirus,  sometimes called stomach flu.

Do viruses spread less in the summer?

Many viruses circulate seasonally and increase as the weather cools in  the fall and winter.  So it’s true that fewer people have stuffy noses and coughs in the summer, but cold weather itself doesn’t cause colds.

It’s not just about seasonality. The other factor is our behavior, experts say. Good weather means people open windows and gather outdoors, where it’s harder for  germs to spread.

But respiratory viruses are still present. When the weather gets too hot and everyone stays indoors and turns on the air conditioning, doctors start seeing more illnesses. In places that are very hot for long periods, summer can be a cold season in its own right.

“I grew up on the East Coast, and everyone gets sick in the winter,” said Dr. Frank LoVecchio, an emergency physician and researcher at Arizona State University. “A lot of people get sick in the summer here. Why is that? Because you spend more time indoors.”

With the spread of stratus, is it necessary to receive another booster of the COVID-19 vaccine?

People who are healthy should consider the timing of any vaccination. A big trip or wedding might be a good reason to get a booster, doctors say. But for most people, it may be worth waiting until the fall in anticipation of a potential surge in  COVID-19 cases  during the winter.

People at higher risk of complications should always talk to their doctor about what’s best for them, she added.  Older adults  and those with weakened immune systems may need more boosters than others, she said.

Are more young children getting COVID-19?

Last month, the CDC noted that emergency room visits by children under four were on the rise. That makes sense, Blumberg said, because many  young children are getting the disease for the first time or are not vaccinated.

Health Secretary Robert F. Kennedy Jr. said in May that vaccines would no longer be recommended for healthy children, a decision that health experts say lacks scientific basis. The American Academy of Pediatrics still supports COVID-19 vaccines for children older than six months.

What other ways can I reduce my risk?

The same things that help prevent colds, flu, and COVID at any other time of year work in the summer, doctors say.

It is recommended to spend time outdoors whenever possible, wash your hands, and wear a mask. And if a person is sick, they should stay home.