Like many Canadians, you may be wondering whether to be vaccinated against influenza. You know that elderly people and those with compromised immune systems can suffer life-threatening complications from the flu—but you’re healthy, so shouldn’t you be able to weather it if you catch it? Maybe, too, you’ve heard about a controversy around the use of thimerosal in influenza vaccines. (This is a mercury-based preservative that some suspect of having harmful effects.) What should you do? For the answers, we looked at reports from the Public Health Agency of Canada, the Centers for Disease Control and Prevention in the U.S., and the National Advisory Committee on Immunization (NACI). We also talked with Dr. Joanne Langley, a Halifax pediatrician who chairs that committee.

What is the flu vaccine?

Each year, different influenza strains become dominant. The World Health Organization determines the makeup of each year’s vaccine based on its analysis of which strains are likely to cause the most trouble. For the 2008-2009 season, it has zeroed in on a couple of strains first seen in Australia and one originating in Florida. The flu vaccine is made from inactivated viruses grown in fertilized hens’ eggs. It cannot cause the flu, and the most common side effect is a sore arm, which may last for a couple of days.

It’s a good idea for everyone to get vaccinated, says Langley, but the highest priority goes to people with a greater risk of developing complications from the flu: children between six and 23 months, seniors, people with certain chronic medical conditions (such as heart and lung disease, diabetes, cystic fibrosis, cancer and metabolic disease), as well as residents of nursing homes and other chronic care facilities. Caregivers for these individuals should also be vaccinated because they can transmit the flu to those at high risk for complications. Last year, Canada added healthy pregnant women to this list. (The flu shot is safe for women at all stages of pregnancy.)

Benefits of the flu vaccine

• Studies indicate that when the match between the vaccine and the circulating viruses is good, there are 70-90 percent fewer cases of the flu among healthy vaccinated adults under 65. Even when there is a mismatch, as was the case last year, there were 50 percent fewer cases of the flu in those who were vaccinated.
• Young adults who get the flu shot take fewer days off work, visit the doctor less often, and take fewer antibiotics and over-the-counter medications. They are also less likely to end up in hospital.
• The flu shot is considered the best defence against influenza. Anti-viral drugs are a secondary defence. These are sometimes prescribed during an outbreak to prevent influenza in people who have not been immunized or to lessen the symptoms in people who come down with the flu. Recently, however, some influenza strains have developed resistance to an antiviral called amantadine, so it doesn’t work as well. The NACI no longer recommends its use. Last winter, some flu strains, mainly in Europe, developed resistance to another anti-viral drug, oseltamivir (Tamiflu). So far, it is still considered effective against strains circulating in Canada.

Concerns about the flu vaccine

• Thimerosal is a mercury-based preservative that has been used since the 1930s in a variety of medications and cosmetics. It is used to prevent bacterial infections, which can be an issue in multi-dose vaccines. Because mercury is a known neurotoxin, controversy has swirled around this additive, raising suspicions that it might be linked to autism. However, studies that have looked at thimerosal in routine childhood immunizations could not establish a link. The form of mercury in thimerosal, ethylmercury, is flushed quickly from the body (unlike its cousin, methylmercury, which accumulates and causes neurological damage). Nevertheless, the pharmaceutical industry is working on removing thimerosal, to increase patients’ confidence. It has already been removed from most vaccines—however, hepatitis B vaccines and most flu vaccines still contain it.
• If you’re allergic to eggs, or have had an allergic reaction to previous flu shots, you should talk with your doctor about the pros and cons of vaccination.

Flu vaccine: the bottom line

Pay attention to risk factors—your own and those of the people around you. And if you dread the annual misery of coming down with the flu, you really can increase your chances of avoiding it.

What do you think about the flu shot? Will you be getting it this year? Share your views in the Comments section below.

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