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New Tack on Preventing Flu

Recent studies show that children are the main spreaders of influenza in a community, and that vaccinating children dramatically reduces the impact flu has on a community during flu season.

Each year, about 36,000 people -- mostly elderly -- die from flu and its complications.

The studies in children are one reason the Centers for Disease Control and Prevention is expanding its flu-vaccine recommendations this year. Before, the CDC advised vaccinating infants between 6 months and 23 months. Now, it says healthy children between 6 months and 5 years should be vaccinated.

Also new this year: The CDC is recommending vaccination for adults of any age who have household contact with children younger than 5, including any out-of-home caregivers. The CDC also advises that children younger than 9 get two doses of vaccine if they've never been vaccinated before.

Vaccination is not recommended in situations where a person with AIDS or another immune deficiency might come into contact with someone who's been recently vaccinated.

Two Types of Flu Vaccine

The most familiar vaccine is the flu shot, which contains the three strains of flu that experts think will be the most likely to circulate widely during the coming season.

The other is a newer product, FluMist. It's a nasal spray that contains a live, but weakened, form of the flu. The FDA has approved FluMist for healthy people ages 5 to 49 years, based on studies in these age groups. (Studies of other groups are still being evaluated).

Neither vaccine promises to prevent flu in 100 percent of people who get vaccinated. And in some groups, such as the elderly, shots may be less than 60 percent effective overall. Even so, many people who get the flu after being vaccinated have a milder case.

In some studies, the nasal spray has been shown to protect up to 85 percent of children and adults ages 49 and younger.

These numbers also depend on how well each year's flu vaccine -- shot or spray -- matches the strains that actually end up in wide circulation. Also, it takes approximately two weeks for the vaccine to produce full immunity in adults, according to the CDC.

Bad Reactions Are Rare

The risk of a serious reaction to the flu shot is extremely low. Some people experience fever and other flu symptoms for a day or so after a shot. Studies of the spray show no significant increase in flu-like symptoms after the vaccine is taken.

The shot may also slightly raise the risk of getting Guillain-Barre syndrome, a rare but serious neurological disease that affects about 20 Americans annually. The CDC says the shot might produce one extra case of GBS per million people vaccinated, but it is very difficult to study a disease that occurs in so few people. And the risk of dying from the flu -- one in 10,000 -- is far higher than the risk of GBS, the CDC says.

Studies of FluMist found no increased risk of serious side effects compared with placebo.

Public health officials have been concerned for many years that FluMist might theoretically spread the flu in some cases, rather than prevent it. That's because FluMist contains live virus that has been made less contagious.

The flu shot contains killed virus and cannot spread the flu.

One study showed that children vaccinated with FluMist can "shed" live flu viruses for up to three weeks after vaccination, meaning that they spread the viruses found in the vaccine to others. That study, in part, prompted researchers to look at a real-life situation in a day-care center.

They studied 197 children in the center and found that one of 99 unvaccinated children got the flu virus from children who had received FluMist. Four other unvaccinated children might have gotten it from vaccinated children, but the evidence was inconclusive.

In the documented case, the child developed very mild symptoms of the flu. Given this low rate of transmission, and the mildness of the symptoms, researchers say that exposure to vaccinated children may even be beneficial to unvaccinated children -– serving as a type of "passive immunization" against exposure to people with active cases of the flu.

When it was first developed, many experts thought a nasal-spray vaccine would gain wide acceptance, because adults and children generally dislike shots. Yet FluMist still lags in sales far behind traditional shots, partly because it is more expensive than shots.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

Joe Neel is NPR's deputy senior supervising editor and a correspondent on the Science Desk.
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