Flu Vaccine Less Effective Than Expected: CDC

This year's flu vaccine may not be as effective as you think.

— -- Does it seem like everyone you know is getting sick this winter? That may be because this year's flu vaccine isn't as strong expected, according to the U.S. Centers for Disease Control and Prevention.

The vaccine has an 18 percent effectiveness against the dominant H3N2 flu strain, the CDC reports. Earlier in the season, flu shot protection level was estimated at 23 percent.

"There's more data that's come in now, given how much of the flu is caused by this mutated strain of H3N2," ABC News' Chief Health and Medical Editor Dr. Richard Besser told ABC News today. "It turns out the vaccine is even less effective than they thought."

Children have even worse odds: for kids ages 2 to 8, the flu vaccine's effectiveness is just 15 percent, according to the CDC.

Children tend to get more viral illnesses than adults, Dr. Besser said, because they're in physical contact with each other and don't have years of flu exposure built up.

The CDC also reports that the nasal-spray version of the vaccine, which was "recommended especially for young children," Dr. Besser said, "is shown to not be effective at all."

Dr. Besser added that the CDC will not preferentially recommend the nasal spray vaccine ahead of the shot and both will be recommended as options.

It may be the end of February, but we're still not out of the woods for flu season.

"Flu season is winding down," Dr. Besser said, but "there is still flu activity around the country."

"We encourage people who are sick to stay home from school and work, and cover their coughs and sneezes," he added.