Which Flu Shot Should You Get? Here's What You Need To Know

The most standard flu shot is a quadrivalent vaccine.

My kids and I tried something different for our flu shots this year. Instead of making separate visits to my doctor and their pediatrician, we all went to the same place: our local Target, where the in-store clinic offered us each a $5 gift card for getting vaccinated. The visit was convenient: We walked right in without an appointment on a Saturday morning. For the first time, my 5-year old didn't scream as the needle went in. And the boys were thrilled to shop for new toys after their shots.

Just before the injections started, however, I started to wonder which flu shot we were going to get. Was it the same one that we'd get at our doctors' offices or that my husband received at a nearby hospital? Was it the best one? Was there even such a thing as the "best one"?

The number of choices available for getting immunized against influenza is unrivaled in the vaccine world. There are10 varieties of flu vaccine made by multiple companies approved for use in the United States.

Options vary in the way they are produced, the way they are delivered and how many strains of influenza virus they include. Also, unlike other types of vaccines, flu shots are available seemingly everywhere: not just in health clinics and pharmacies but in grocery stores, fitness centers, and pop-up fairs at schools and workplaces.

"Nothing approaches flu in terms of the numbers of products available and the number of different ways they are made," says Paul Offit, a pediatric infectious disease specialist at Children's Hospital of Philadelphia who also serves on the Food and Drug Administration advisory committee that determines which strains to include in the seasonal vaccine. "There are no other vaccines that offer so many choices."

So, what's a confused flu-shot seeker to do?

For most people, simply getting the flu vaccine - any flu vaccine - is what matters most, says David Cennimo, an infectious-disease specialist at Rutgers New Jersey Medical School in Newark. And in practice, most of us don't really end up making a decision at all. Each clinic decides which varieties to carry, so by the time you get there the decision has been made.

Generally, the most standard flu shot is a quadrivalent vaccine, which comes in five varieties that contain the same four strains of influenza most likely to be circulating each season. The shot goes into a muscle, usually the arm. This is what my kids and I got, I learned when I called the Target clinic to ask which shots they generally offer. The woman who answered said they have a few kinds but give most people "the regular one." Pressed for more detail, she told me it was a quadrivalent variety called Fluzone.

Also available are three trivalent options, which contain three strains of influenza instead of four. Offit says one of them, approved for people ages 6 months to 64 years, will probably be phased out over time because it offers less protection than the quadrivalent versions. (If you have received a trivalent version, Offit says, there's no harm in getting a second shot with the quadrivalent formulation.)

If you're 65 or older, however, the other trivalent options are probably your best bet. One, the Fluzone High-Dose, contains four times the number of viral particles that prompt the body to produce antibodies. The other, Fluad, contains a compound called an adjuvant, which induces the immune system to react more forcefully to the injection. Both types address the weakened immune response that happens with age.

Fluzone High-Dose and Fluad are both produced by Seqirus and both work equally well, Offit says. One 2014 study showed that, among nearly 32,000 people, the Fluzone High-Dose elicited more antibodies and was 24 percent more effective at preventing influenza infections compared with a regular-dose flu shot. More recent data from last year suggest the high-dose vaccine was better but less so - offering about 8 percent more protection.

On the other side of the age spectrum, kids who are 2 and up can get FluMist, a quadrivalent vaccine that includes bits of live virus (modified so that they can replicate in the nose but not replicate in the warm conditions of the lungs). The American Academy of Pediatrics has recommended shots over the nasal spray for kids, based on some evidence that FluMist didn't work particularly well in the winters of 2013-2014 and 2015-2016.

But manufacturer GlaxoSmithKline has reformulated a new version of the nasal spray that, Offit says, appears to be at least as effective as the shot. The Centers for Disease Control and Prevention supports both, and FluMist can be a good option for people who hate needles. "We should offer it to young children," Offit says. "I think it's kinder."

Most flu vaccines, including the nasal spray, are still made the old-fashioned way - grown inside chicken eggs. The pharmaceutical company Sanofi Pasteur has taken a different strategy, growing the vaccine in cells instead. Originally, this recombinant flu vaccine, called Flublok, was designed for people with severe egg allergies. But even vaccines grown in eggs appear to be safe for most people with egg allergies.

And because the virus tends to mutate inside eggs, the cell-based vaccine may be more protective overall, suggests a new study, which found that Flublok may be about 36 percent more effective than flu vaccines cultivated in eggs. Last year, the cell-based vaccine also performed slightly better than the high-dose vaccine in older people.

Flublok is more expensive to make and supplies are lower. Still, Offit says his 26-year-old son found a pharmacy that offered it.

Multiple flu vaccines are available as either a single dose, packaged in its own vial, or one that gets siphoned off from a larger vial of liquid. There is no need to seek out one or the other, Cennimo says, even though some people have expressed concerns about preservatives used in the multidose vials.

"It's crazy to worry about this," he says. "The data (show) that it's safe."

As for where to go, some doctors prefer their patients come to their primary-care clinic, because that makes it easier to keep track of who has been vaccinated, says Gregory Poland, director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota. Others don't care. Most agree that it's better to get the shot somewhere than not at all.

"Just get something," says Cennimo, who adds that he asks patients to bring him their records so he knows they've received their flu shot each year. "At the end of the day, as long as you get a vaccine you are much better off than all the people who didn't."