MALTA—U.S. drug stores have been advertising their seasonal flu shots to the public for weeks, and here at Scientific American employees have already been invited to sign up for free jabs next month.

These vaccination enticements, for the most part, come down to individuals' decisions about arming themselves against the flu. But for doctors, nurses and other workers in the health care industry, their level of protection against the season's circulating flu strains has the potential to impact hundreds of others, noted health experts at the fourth European Scientific Working Group on Influenza (ESWI) conference earlier this month in Malta.

If an office worker gets sick, he or she might spread germs to co-workers who sit nearby. But if doctors or nurses get the flu, they can pass it to the dozens of patients they come into contact with each day—many of whom have other conditions that render them more susceptible to infection. The flu still kills thousands of people each year in the U.S., most frequently those with underlying conditions, who also have more frequent contact with medical personnel than the healthy.

Last winter just under two thirds (63.5 percent) of health care workers got a seasonal flu shot, according to an August report published by the U.S. Centers for Disease Control and Prevention (CDC), even though universal vaccination of health care workers is supported by numerous scientific and medical groups.

Why would so many of these workers forgo the protective injection? "There is some question of understanding" as to whether even many health professionals are aware of the limited risks and outsize benefit of the vaccine, Maria Zambon, director of the Center for Infections at the U.K.'s Health Protection Agency, said at ESWI.

Many of those in the health care field who opted not to get the shot did not think that the vaccine "was worth the time and expense" or that it could "protect them and the persons around them from the disease," according to the CDC report. About 40 percent of the health workers who did not get vaccinated said that they did not consider influenza a serious threat to the health of people around them—and about 55 percent said that they did not think the vaccine would protect those around them.

And as tough as they can be, the immune systems of doctors and nurses are not impervious to influenza. Unvaccinated health care staffers are second only to unvaccinated adults living with kids in their likelihood of coming down with the flu. About 18.7 percent of unvaccinated health workers versus 24 percent of unvaccinated adults with children in the home get the flu each year, according to Allison McGeer, a microbiologist and infectious disease consultant at Mount Sinai Hospital in Toronto. That means "health care workers are at higher risk of influenza than other working adults," who have an annual infection rate of just 5.4 percent, she said at the ESWI meeting. And her analysis suggests that health workers tend to have a higher rate of asymptomatic infections, which "may say something about the risk of influenza transmission to patients."

Hospitals mandating vaccination for employees have raised the hackles of some unions and professional associations. States and local governments can also exercise their rights to pass mandatory vaccination laws for certain groups (such as school children, military enlistees or health care workers), according to a congressional report (pdf) produced earlier this year.

For medical institutions that have adopted a requirement that their employees get the shot, their rate of vaccination was 98.1 percent last flu season, according to the CDC report. Another study found hospitals that introduced vaccination requirements mid-season last year increased the rate of employee flu shots 62 percent to 76.6 percent. "Hospitals that are unable to improve suboptimal influenza vaccination coverage through multifaceted, voluntary vaccination campaigns may consider institutional requirements," noted the authors of the paper, which was published online September 22 in Vaccine. "Rapid and measurable increases in vaccination coverage followed institutional requirements." These employers still seemed to be in the minority, though, with only 13 percent of respondents in the CDC study reporting that they had been required to get the shot.

Another policy that has boosted shot rates in some hospitals, just shy of a full-coverage mandate, is the condition that any employees who decline the vaccination be required to wear a surgical mask for the duration of the flu season—even if that employee does not work with patients. "That means that individual is stigmatized, whether or not the face masks are doing a good job of preventing transmission," Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health, said at the ESWI. The mask policy, for example, increased uptake of the vaccine from 70 to 96 percent at one Massachusetts hospital, The Boston Globe reported earlier this month.

Improving uptake of the seasonal flu vaccine among health workers could also improve response to a pandemic in the future by creating wider immunity to a number of strains and by habituating people to getting the shot. "If we get it right for influenza, it will help us to be better prepared for other infections," Zambon said. But, she added, those in the health care industry are a crucial barometer: "If we are unable to convince them about the vaccine," the rest of the population might be even more challenging to rally. During the 2009 H1N1 pandemic, for example, only slightly more than a third (37 percent) of health care professionals ended up getting the shot when it became available.

Monto calls the decision to pass up the vaccine—whether you are a health worker or not—"stupid behavior," noting that the demonstrated benefits to yourself and those around you far outweigh any slight risks of adverse reactions.

McGeer put it a little more diplomatically, noting that there is "no question in my mind, from a scientific point of view, that no one should be working in health care without being vaccinated."