By Brenda Goodman, MAWebMD Health News

Reviewed by Brunilda Nazario, MD

Feb. 26, 2015 — It’s no secret this year’s flu shots didn’t work as well as doctors had hoped. But the news got worse Thursday when the CDC revised its estimates of the flu vaccine‘s effectiveness downward even further, from 23% to 18%.

That means for all ages, getting vaccinated cut the risk of needing medical treatment for flu symptoms by just 18%.

“That’s crummy, at best. This year was a bum year,” says William Schaffner, MD, an infectious disease expert and a professor at the Vanderbilt University School of Medicine in Nashville, TN.

And there’s more bad news: Early numbers show that for the second flu season in a row, the FluMist nasal spray, aimed mainly at children, didn’t work at all for kids ages 2 through 8.

That was a bit awkward for the CDC, which had just advised doctors that they choose the nasal spray over the shot for younger kids. Previous studies had suggested that FluMist was more protective than injections for kids in this age group.

Today the agency’s advisory committee changed its position, telling doctors to use either kind of vaccine in children, with no particular preference for the nasal spray.

The vaccine-effectiveness percentage is just an average. The real effectiveness probably sits in a range between 6% and 29%, says Brendan Flannery, PhD, of the Center for Immunization and Respiratory Diseases at the CDC.

When the vaccine is a good match to the strains of flu making people sick, vaccine effectiveness has been as high as 60%.

This season’s dominant flu strain, H3N2, is different from the strains included in the flu vaccine, though.

So far this season, 86 children have died of the flu, and more than 13,000 people have been hospitalized with it, according to the CDC. The highest rate of hospitalizations is in adults older than 65. Most adults who’ve had to go to the hospital have had at least one underlying medical condition.

Experts say even though this flu season’s vaccine wasn’t up to par, people shouldn’t give up on getting their annual flu shots.

“Year in and year out it prevents much disease, many hospitalizations, and it prevents some deaths, so we have to use the technology that we have available today,” Schaffner says.

“Down the road, all of us have our fingers and toes crossed, we’re hoping for the so-called universal influenza vaccine, which is tantalizingly out there now in early clinical trials. It may be in 5 years we have a vastly improved influenza vaccine, but this is the one we have now,” he says.

Problems With Nasal Spray

Meanwhile, other experts presenting to the CDC advisory committee tried to get to the bottom of another mystery. For the past two flu seasons, the nasal spray FluMist, which contains a live, but weakened form of the flu virus, hasn’t worked in children, the group of people the vaccine was really intended to protect.

In the 2013-14 season, the nasal spray had no measurable effectiveness against the H1N1, that season’s dominant strain. Flu shots, though, were about 60% effective for kids.

Kathleen Coelingh, senior director of medical affairs at MedImmune, the company that makes FluMist, says one of three flu strains included in the vaccine — the A/California strain, which protects against H1N1 flu — was vulnerable to heat. Some lots of the vaccine were left outside refrigerated warehouses during shipping for hours at a time.

A company study found that when the vaccine was shipped during colder months, it was more effective than when it was shipped during the warmer summer months.

This year, FluMist is also performing badly in children, Coelingh says. But she says that’s also because of the same problem that’s plagued all vaccines: “the mismatch” between the vaccine strains and the ones that are making people sick “is really bad,” she says.

Coelingh says the company is working to replace the heat-sensitive strain with one that’s more heat-stable.

SOURCES: Meeting, The Advisory Committee on Immunization Practices, Feb. 26, 2015. William Schaffner, MD, professor of preventive medicine, Vanderbilt University School of Medicine, Nashville, Tenn. The Centers for Disease Control, “Weekly U.S. Influenza Surveillance Report.”

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