Blog | Friday, March 22, 2013

Was this year's flu vaccine good enough?

Let me tell you about two patients.

Mr. S is thirty years old. He shuffled into the office in a sweatshirt and pajama bottoms. Black unwashed hair stuck out from a black and silver toque. He looked like he was keeping his head up by sheer force of will, and had no energy left for shaving or other trivialities.

He had a sore throat, a cough, and a fever of 103. He didn't have a flu shot, and tested positive for influenza.

He went home with advice to get some rest and drink plenty of fluids. His wife and children had their flu shots earlier in the year and did not become ill.

Ms. R is eighty. She started to cough and over the course of a couple of days became weak and had trouble breathing. In the emergency department she was found to have influenza and was admitted for IV fluids and oxygen therapy.

A few days later her condition worsened. In the middle of the night she was transferred to the ICU and put on a breathing machine. A chest X-ray showed pneumonia.

Two weeks later she was discharged to a nursing home, and eventually returned to her own apartment. She had a flu shot two months before her illness.

A widely-cited statistic says that this year's flu shot is "62% effective," whatever that may mean. For Ms. R, it was 0% effective. She developed pneumonia as a complication of her flu and was lucky to survive.

What accounts for these different stories? Many people, especially young people, have been spared the flu this season because of the flu shot. But older folks haven't done as well.

A recent Morbidity and Mortality Weekly Report, a publication of the U.S. Centers for Disease Control and Prevention, describes the situation in an update on the efficacy of this year's shot. Influenza A (H3N2) is one of the subtypes in this year's shot, and also a really nasty bug. It tends to cause more severe disease than other influenzas, and has been a big player this season. It turns out the shot has done a good job against this guy, reducing flu-related doctor visits by one-third to one-half. Older folks haven't done so well.

So far this year, the flu shot has failed to show a significant drop in doctor visits for people over sixty-five. This is on par with previous data on flu vaccines. Some studies have shown much less benefit in older adults. But some studies have looked at different end-points, such as death from all causes, or pneumonia or heart attack. Many of these studies have been more encouraging.

The long and short of it is, the flu shot seems to be cutting back significantly on flu cases, which will benefit us all. Since those most vulnerable aren't as well protected by the shot, they will benefit from those around them being vaccinated. If you aren't exposed to the flu, you can't catch it.

The way to protect those who aren't protected by the shot is to vaccinate as much of the population as possible so that we can all benefit from "herd immunity." The flu shot is still a good idea for everyone over 6 months of age.

Peter A. Lipson, ACP Member, is a practicing internist and teaching physician in Southeast Michigan. After graduating from Rush Medical College in Chicago, he completed his internal medicine residency at Northwestern Memorial Hospital. This post first appeared at his blog at Forbes. His blog, which has been around in various forms since 2007, offers "musings on the intersection of science, medicine, and culture." His writing focuses on the difference between science-based medicine and "everything else," but also speaks to the day-to-day practice of medicine, fatherhood, and whatever else migrates from his head to his keyboard.