Which Flu Shot Is Right for You?

HealthMap Vaccine Finder (flushot.healthmap.org) is a handy tool for finding a flu shot provider by town or ZIP code. The site lists the types of vaccines offered, but it's a good idea to call ahead to check on supplies.

Flu vaccine options vary according to a person's age. Here are some questions and answers to guide you:

If You're Age 65 and Older

The choices include the regular flu shot (standard dose of the trivalent), the high-dose flu shot (double dose of trivalent), the quadrivalent flu shot (a new four-strain version) and the egg-free shot called Flucelvax.

Should you get the high-dose vaccine or standard one?

Talk to your doctor about whether you need a high-dose vaccine, but studies do show that people who receive the high-dose vaccine produce more antibodies — infection-fighting proteins in the blood — than those who get the regular dose. That's important because vaccines work by provoking the immune system's defenses against the target disease, and older people tend to mount a weaker response.

In fact, the high-dose vaccine was developed to address concerns that the standard-dose shot doesn't work very well in people 65 and older, the very group most likely to be hospitalized or die from flu complications. Last year, for example, the CDC reported that season's regular vaccine lowered an older person's risk of flu by only 27 percent, an unexpectedly low level of effectiveness compared with a 63 percent reduction for people ages 50 to 64.

Whether the high-dose shot's effect on blood antibodies will translate into substantially fewer people getting sick is not yet clear. But signs are good that it offers at least some advantage. In August the vaccine's maker, Sanofi Pasteur, issued preliminary findings from an ongoing clinical trial showing the higher dose increased flu prevention by 24 percent over the standard dose.

What about the new quadrivalent vaccine?

While the high-dose shot seems to offer stronger protection against flu, the quadrivalent shot gives broader protection. Every year public-health authorities design the trivalent vaccine to build immunity against the three strains of flu deemed most likely to circulate that season — two strains of type A flu and one strain of type B.

The trouble is, two separate subtypes of B virus are common causes of illness, and it's not easy to predict which one will predominate in a given year. "We're wrong about half the time," says Gregory Poland, M.D., a vaccinologist who founded and leads the Vaccine Research Group at the Mayo Clinic in Rochester, Minn.

The quadrivalent shot solves that by including both common B subtypes, so its protection is broader. However, the B viruses tend to be more virulent in children, while the A strains are more likely to cause severe illness in older people. For this reason, all three experts we spoke with recommended that people 65-plus get the high-dose standard shot — with its extra dose of A-strain vaccine — rather than the quadrivalent. The high-dose also may be easier to find than the quadrivalent, which is in shorter supply.

If You're Ages 50 to 64

The choices include the regular flu shot, the new quadrivalent flu shot, the tiny-needle shot and the egg-free Flucelvax.

Should I get the quadrivalent vaccine?

For somewhat younger adults, the quadrivalent shot may be ideal in terms of protection against flu. But here as well, studies have yet to prove superior performance over regular vaccine. And because it's brand new this year, supplies are limited. Zimmerman says that if all the alternatives were offered at the same price, for people 50 to 64 he'd choose the quadrivalent vaccine. "However, I would not travel an extra 20 minutes for it," he adds.

Is the tiny-needle shot a good option?

Those wary of needles can also opt for the tiny-needle or "intradermal" shot, which deposits the medicine under the skin rather than in the muscle, as a standard shot does. It's been approved for people ages 18 to 64 and protects against three viral strains, same as the standard flu shot. It also can be harder to find than the standard flu shot.

What about the egg-free vaccine?

Anyone 18 or older who is hypersensitive to eggs — a problem that's actually far more common in young children — can choose a vaccine whose virus is grown in mammalian cells rather than chicken eggs.

Katharine Greider is a freelance writer.