HOUSTON—Experts analyzed the flu shot in 2007 after the Centers for Disease Control found it was ineffective for over half of the circulating flu viruses.

“Usually every ten years the virus Influenza A and B, and what happened usually the virus changes a little bit every year. But every ten years is a major change,” Dr. Lela Vizirov, from Memorial Hermann Hospital, said.

Doctors say the flu virus drifted last year.

So while the shot was crafted to prevent illness for specific strains of influenza, the virus mutated and last year’s shot became much less effective.

“This year we have better coverage, better protection for our population,” Vizirov said.

After FDA recommendations, manufacturers changed all three strains of the flu virus contained in the shot. That’s something that hasn’t been done in years.

Usually only one or two strains are changed, but after last year’s virus drift these changes are expected to better protect patients.

“To me, it kind of helps me because I’m out in the weather all the time anyways,” patient Kevin Redden said.

Redden works in construction and despite last year’s flu shot fumble, like most people, he still gets his shot every year.

A nasal spray is also available this year, but Dr. Vizirov explained it’s not for everyone.

“If somebody has an immune deficiency: pregnant, older than 50 years old, cannot give it to them,” said the doctor.

Influenza peaks in February. Doctors say a shot now will protect you for the entire season.