Sept 22 (Reuters) - Expert advisers to U.S. Centers for Disease Control and Prevention (CDC) on Friday recommended Pfizer's respiratory syncytial virus (RSV) vaccine for women in the middle of the third trimester of pregnancy to protect their babies from severe illness.

That Pfizer shot and one developed by GSK in May became the first two RSV vaccines to win U.S. approval, for use in people aged 60 and over to prevent severe illness. In August, Pfizer's vaccine also won approval for the maternal use. Here's what you need to know.

What is RSV?

RSV is a usually seasonal respiratory virus that generally causes mild, cold-like symptoms. Still, infants and older adults have a higher risk of developing severe RSV.

RSV leads to 58,000 to 80,000 hospitalizations among children under age 5, and 60,000 to 160,000 hospitalizations among adults age 65 and older each year, according to the CDC. It causes around 14,000 deaths in adults aged 65 and older in the U.S. annually, according to government estimates.

Who should get the vaccines?

The U.S. CDC has recommended that adults aged 60 or older may get the shot after discussions with a healthcare provider about whether RSV vaccination is right for them. The agency stopped short of saying all adults over the age of 60 should receive it this year.

Outside advisers to the CDC suggested the narrower recommendation in June after expressing concern that there was not sufficient data on how effective the vaccines are in people over age 75 and in other high-risk groups.

The CDC will make its formal recommendation on use of the vaccine in expecting mothers to protect infants up to age 6 months after weighing the views of members of its Advisory Committee on Immunization Practices. The panel recommended use of the shot in women 32 weeks to 36 weeks into their pregnancy from September to January, in order to protect babies born in peak RSV season.

How often do I need to get the vaccine to stay protected?

Early data suggests that the RSV shots are protective for at least two years, but it is not yet clear how often older adults will need to be revaccinated. CDC advisers will consider the frequency of revaccination when more data becomes available.

What else is available to protect infants from RSV?

In July, the FDA also approved Beyfortus, a long-acting antibody therapy from Sanofi and partner AstraZeneca , to prevent RSV in children up to 24 months of age.

Previously, Swedish Orphan Biovitrum's Synagis was the only approved preventive therapy in the U.S. for high-risk infants. Synagis is given as monthly injections, while Beyfortus can be given annually.

Are RSV cases on the rise?

Yes, although not alarmingly so. Detection of the virus in testing has increased significantly over the last month to around the same levels as this spring, according to CDC data. Still, that is a fraction of the positive tests recorded at the same time a year ago, when RSV cases were surging around the country and hospitals were running out of pediatric beds.

Can I get the RSV shot alongside my COVID and flu shots?

Yes, current CDC guidelines allow for all three vaccines to be administered simultaneously, even though they have not been tested together.

"If it's now or never again, it's best to get all the vaccines you're eligible for to get the protection against as many diseases as possible," said Dr. Jeffrey Duchin, a member of the board of directors for the Infectious Diseases Society of America. "If you've got the luxury of returning for more than one visit, you can choose to space them out."

Will my insurance cover it?

Adults who are insured under the U.S. Medicare program for people aged 65 and older or disabled are covered for the vaccine. Many private insurance plans, including large insurers like CVS Health's Aetna, Humana and Elevance , which owns Blue Cross Blue Shield insurers including Anthem, also say they are covering the shot for adults 60 and older who are not yet eligible for Medicare. Typically you do not need a prescription. Keep up with the latest medical breakthroughs and healthcare trends with our newsletter Reuters Health Rounds. Sign up here. (Reporting by Michael Erman in New York; Additional reporting by Bhanvi Satija in Bengaluru Edtiting by Caroline Humer and Bill Berkrot)