Until 2003, there was only the flu shot. A needle in the arm delivered vaccine, and a couple of weeks later your immune system was primed to fight off the top three strains of influenza likely to be floating around that winter and early spring.
But over the past several years, flu vaccine developers and manufacturers have been doing a lot of tinkering. They've come up with at least seven different types of vaccine and/or delivery modes.
There are options for people who haven't been able to get vaccinated because of an allergy to eggs; for those who hate needles; for those who hate needles injected into muscle and for older people with balky immune systems who might need a stronger dose to gain protection; plus new lines of vaccines that protect against an extra strain of flu virus.
In all, manufacturers have told the federal Centers for Disease Control and Prevention, or CDC, that they expect to produce at least 135 million flu vaccine doses for distribution in the U.S. this season, with more than 73 million doses already delivered to doctors' offices, clinics, pharmacies, hospitals and other outlets.
Last year, the flu season got an early start in October. Many officials fear the same pattern may repeat this fall, prompting an early "get a flu shot" campaign that rivals the Christmas promotions by some retail chains.
The CDC and other public health advocates recommend flu vaccination for anyone 6 months or older (younger babies' immune systems aren't geared up enough to get it). Last year, an estimated 56 percent of children and 42 percent of adults got the flu vaccine. Children younger than 9 getting a flu shot the first time need two doses.
"We have more types of vaccine available than ever before, and there are one or more options that are right for everyone,'' Dr. William Schaffner, an infectious disease specialist at Vanderbilt University and past president of the National Foundation for Infectious Diseases, said at a Sept. 26 briefing sponsored by the foundation.
All flu vaccines will include strains of H1N1 and H3N2 and a strain of influenza B. The three-strain or "trivalent" vaccine represents the bulk of vaccine stocks available this season. Some lines are made using a virus grown in eggs and can be given to anyone 6 months and older; others are grown in a cell culture and are approved only for patients 18 years and older.
The four-strain, or quadrivalent, vaccine is the big innovation for this year, protecting against a second B-type influenza that mainly sickens young children. It's available as a shot and as a nasal spray, which is limited for use on healthy people 2 to 49 years old.
Vaccination experts expect the four-strain dose will replace the three-strain version in all products within two to five years, but the CDC says it will make up less than a quarter of vaccine supplies this year.
Quadrivalent vaccines will cost a third to a half more, according to some prices in government contracts and trade reports. For instance, one manufacturer's price per dose to the CDC is $12.03 for the four-strain and $8.08 for the standard three-strain version.
Another three-strain version can be delivered with barely a tingle by an array of tiny, short microneedles into the skin, rather than by a single needle into muscle.
And for people sensitive to eggs — which is roughly 1 percent of adults and 4 percent of children — there's a new egg-free, three-strain formula. The vaccine is cultured in caterpillar cells.
There's also a high-dose vaccine intended for people 65 and older whose immune systems are less responsive and may need a bigger virus challenge for flu protection.
Although the four-strain vaccines clearly cover more ground, CDC officials say that all FDA-approved vaccines offer good protection and that no strong evidence suggests one type is superior.
"There are lots of open questions, and each year is different,'' said Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.
Because individual immune systems differ and flu vaccines may not perfectly match the virus going around, no vaccine can guarantee you won't get sick. But even if you do, the illness is likely to be shorter and milder than without a flu shot.