How Well Does the Vaccine Work in the Elderly?

Tuesday, October 25, 2005

Despite 64 published studies over the past 35 years, we really don't know how well the flu vaccine works to prevent serious illness and death in the elderly. How is this possible? The answer has to do with how the studies were done.

Fifty-nine of the 64 studies were observational; that is, studies where scientists simply count up outcomes (e.g., the number of flu-like illnesses among people who did or did not get the vaccine). Observational studies cannot prove cause and effect. And findings that are encouraging -- for example, fewer deaths observed among those vaccinated -- may not mean the vaccine works. Rather, such results may simply reflect that the people who get vaccinated are generally healthier than those who do not.

The five remaining studies were randomized trials -- the gold-standard experiments most trusted in science. None of the five looked at the vaccine's effect on flu-related death; what they looked at instead was the vaccine's effect on getting the flu or a flu-like illness. The results suggest that flu shots have a larger effect in nursing homes than in the community at large.

© 2005 The Washington Post Company