HCW study probes flu vaccine’s effectiveness

Take a long-term view of vaccine, expert says

If public health authorities want to convince health care workers to get vaccinated against influenza, they won’t mention a recent study at a Denver hospital. It found that this year’s vaccine did not reduce the likelihood of getting influenzalike illness.

Yet that study is far from the final word on the subject. Its major weakness: It did not measure how well the vaccine protected against lab-confirmed influenza.

"If you look at other studies, in previous years where there was not an exact match between the circulating virus and what was in the vaccine, the cruder studies that used influenzalike illness all showed much lower vaccine efficacy rates than did the studies that came along later, that took much more lab work to use laboratory confirmed influenza," says William Schaffner, MD, who is chair of the department of preventive medicine at Vanderbilt University in Nashville, TN.

"This is the first of many studies of vaccine efficacy that are going to be done," explains Schaffner, who is also on the board of the National Foundation for Infectious Diseases, which made flu vaccination of health care workers a priority goal this year. "This is kind of an expected result."

Furthermore, the survey had a response rate of 61%. The health care workers who failed to respond may have been the healthier ones, notes Schaffner. "You have to wonder who didn’t hand back the survey," he says. "My sense is that well people didn’t hand back the survey so that the survey is going to be biased in terms of survey results."

The survey was distributed in paper and e-mail form to 3,100 employees of The Children’s Hospital in Denver. Of 1,818 respondents who completed the survey, 78% were vaccinated.

Overall, 289 (16%) of respondents reported having influenzalike illness; an analysis found no significant difference in the "attack rate" among those vaccinated and those not vaccinated.1

Future studies will look at the impact on lab-confirmed influenza and on serious complications related to influenza. Even when a vaccine is not well matched with the circulating strains, as happened this year, it may provide significant benefit in preventing influenza-related deaths and serious complications, the Centers for Disease Control and Prevention reported.

Health care workers need to take a long view of the influenza vaccine, Schaffner stresses. They receive the vaccine not just to protect themselves, but also to protect their vulnerable patients.

"Influenza vaccine is not a perfect vaccine, but it is a pretty darn good vaccine. Every once in a while — every six to 10 years — there’s not going to be a perfect match between what’s in the vaccine and the circulating virus," he explains.

"We should not be making decisions about whether or not to get the vaccine on an annual basis. We should get vaccinated annually," says Schaffner. "We’re interested as health care workers in doing the best we can do in preventing our transmitting influenza to our patients and to remain healthy on the job when we are most needed and not to bring flu home to our families. The best way to do that is to get vaccinated every year."

Reference

1. Dolan S, Nyquist SC, Ondrejka D, et al. Preliminary assessment of the effectiveness of the 2003-2004 inactivated influenza vaccine — Colorado, December 2003. MMWR 2004 53:8-11.