Subjects: Public health
Efficacy data on flu vaccine is decidedly mixed, surprisingly enough.
Many trials suggest it has a beneficial effect. For example, an October, 2007 meta-analysis in NEJM pooled the results of 18 studies involving 713,872 elderly people and concluded the vaccine cut hospitalizations for flu and pneumonia by 27% while reducing all-cause death rates by 48%.
Those findings confirmed a March, 2002 analysis in which non-institutionalized elderly folks who received flu vaccine experienced 35% fewer flu-like illnesses and a 50% lower mortality risk than those who didn’t take the spike.
But many well-designed trials conclude the vaccine is ineffective. The most recent of these, published in Lancet in August, 2008 showed that flu vaccine had no impact on the risk of community-acquired pneumonia in a cohort of 4,000 elderly people.
That study confirmed a February, 2005 piece in the Archives of Internal Medicine which concluded that flu-related mortality reductions in the early 1970s were attributable to immunity acquired during the pandemic of 1968, not the vaccine.
These scientists also noted that although vaccine coverage skyrocketed from 15-20% in 1980 to 65% in 2001, there was no associated drop-off in flu-related mortality.
So what’s a mother to do, not to mention everyone else that’s supposed to queue up each fall for the jab?
Authors of the negative studies who were interviewed by Amednews say flu vaccine does work, just not all that well.
“The true benefit is somewhat unknown,” Lisa Jackson , a co-author of the Lancet piece told Amednews.
“It’s reasonable to continue getting influenza vaccine, but we need a more realistic message about the benefits (people) might expect. (A) 50% reduction in all-cause mortality is just not plausible,” she added.
A randomized controlled trial of flu vaccine in the elderly population would settle the matter, but that’s not going to happen for ethical reasons.
A more fundamental problem is that the flu virus morphs into a different beast every year, and vaccine makers are in constant catch-up mode. There’s no way to generalize results on vaccine efficacy from year to year.
For example, an article appearing in last month’s Journal of Infectious Diseases concluded that flu vaccine prevented an infection requiring medical attention just 5% of the time during the 2004-05 season, but the 2006-07 version prevented these visits 37% of the time.
More than 143 million flu vaccines were delivered this season.