2007-08 Flu Season: A Seasonal Checkup

By the time calendars turned over to January, it appeared the 2007-2008 season would not be a knock-out year for the flu. Rates had been low in the nation since the beginning of flu season in October. All signs indicated the U.S. population had influenza in check.

But in February, the Centers for Disease Control and Prevention began receiving reports of widespread flu activity. Weren’t the vaccines working? Why was flu creeping up late in the season?

While people across the country still huddle under bedcovers, MSN consulted the CDC and Dr. William Schaffner, chair of the Department of Preventive Medicine at the Vanderbilt Medical School in Nashville, Tenn., and member of the Infectious Disease Society of America’s Immunization Workgroup. We sought a late-season diagnosis of this year’s flu, and asked what lessons are being learned about fighting influenza with vaccine.

Taking aim at a virus

“As flu researchers and health care professionals say, ‘If you’ve seen one flu season, you’ve seen one flu season,’” Schaffner quips, a reference to the ever-changing challenges of fighting influenza with vaccine. Influenza is a mutating virus; unlike a disease such as measles, the active strains are different every year. Given the lead time needed to research, produce and distribute the annual vaccine, “You cannot predict with certainty eight or 10 months in advance which strains will be circulating,” he explains. “Flu is simply too iffy.”

We were off to a good start this season. Of the three viruses this year’s vaccine aimed to cover, the two primary, or “A,” strains were well addressed. It’s the late-coming “B” virus, a minor strain, that is causing widespread illness now. “The minor strain usually causes less severe disease and more localized outbreaks but it’s becoming more common this year,” Schaffner says. “I have a feeling that’s because the other two strains were so on-target. There was a partial mismatch — exactly how much won’t be determined for months.”

The CDC’s track record on matching vaccines to strains is actually quite good — even excellent, in Schaffner’s view. “We can’t get 100 percent on the exam, so to speak, but if you’re up over 80 percent, that’s as good as you can expect all the gray-haired eminences who study flu full-time to do.” According to the CDC, vaccines have been well matched to predominant circulating viruses in 16 of the last 19 U.S. influenza seasons. That’s an 84 percent success rate, which is right in Schaffner’s ballpark.

Get the shot?

If you received the flu shot for this season and still got sick, you may be thinking it isn’t worth a stick in the arm next year. It’s an understandable perspective, to be sure, but science is not on your side.

You quite simply stand a better chance evading the flu if you have the shot than if you don’t. The vaccine is not foolproof, but even mismatched vaccines offer some cross-protection against related strains of the virus. “Protection is rarely zero from the vaccine,” says Schaffner. “If you don’t expect perfection, you won’t be disappointed.”

One major deterrent to getting the shot is the dogged perception that one can acquire the flu from the shot. Though health providers are specific that it’s impossible—vaccines  carry only inactive virus, not live strains—try telling that to someone who has fallen ill just days after receiving an inoculation.

“We have the problem of trying to sort out coincidence from causality,” says Schaffner. “Just because X follows Y doesn’t mean X caused Y.”

Studies repeated each year show that symptoms appear at the same rate in people who have received vaccine as in people who have received a placebo. Between 1 percent and 5 percent of both groups experience symptoms after their shot.

“You could get inoculated with peanut butter! Still, 1 to 5 percent are going to experience a cold-like illness within the following week or two,” Schaffner says.

Blaming the flu vaccine for an illness is also indicative of our need to hold someone or something responsible when we feel lousy. What we forget, though, is that people can spread viruses days before they show signs of illness. The individual who passed along his/her flu may have exhibited no symptoms whatsoever. And when we don’t remember being around anyone who seemed sick, we blame that damned flu shot.