The 2017–2018 flu season reached epidemic proportions for 16 consecutive weeks. According to the Centers for Disease Control and Prevention, the flu was responsible for a record number of hospitalizations, as well as more than 80,000 U.S. deaths, the highest number in over a decade and at least 25,000 more than the previous year.
Even though the flu is a serious health issue, many people drag their feet when it comes to getting vaccinated. Typically, only about 40 percent of adults get flu shots. Pedro A. Piedra, a physician and researcher at the Vaccine Research Center, would like to see that number (called flu coverage) rise to 80 percent.
People cite all sorts of reasons for opting out of vaccination. Some fear they’ll get sick from the flu shot itself, while others distrust vaccines generally, or believe the vaccine is pointless since it doesn’t protect against every flu strain. Still others assume that a flu-free past means a flu-free future. But in the vast majority of cases, experts say there’s no justification for riding out the flu season without protection.
“Last year was a severe year for influenza. We had high attack rates, high hospitalizations and high mortality in both children and older adults,” said Piedra, who is also a professor of virology and microbiology at Baylor College of Medicine in Houston. “What will happen this year, we can’t predict. But I can say that the flu will circulate and will cause problems, and the best way to protect yourself from it is to be vaccinated.”
The flu shot: backstory and basics
The influenza virus was first isolated in a laboratory in the early 1930s, and a vaccine has been in use since the end of World War II. The flu isn’t a single virus: Instead, there are two main types of influenza, A and B, each with multiple strains. The diseases caused by all of these viral strains are collectively called “the flu,” and between 9.2 million and 35.6 million people get it every year. The vaccine helps the body produce an antibody response that will prevent viral infection.
Early flu-shot guidelines focused on vaccinating high-risk populations, meaning children, the elderly and people with compromised immune systems. Once Medicare began covering flu shot costs for patients in 1993, vaccination became more widespread in the U.S. In 2010, the CDC began recommending flu shots for everyone 6 months old and up.
The disease primarily spreads via the mouth, nose and eyes when infected people talk, cough and sneeze. It’s also possible to pick up the flu if you touch a surface harboring the virus and then touch your face, although this mode of transmission is less common. Symptoms can include fever, body aches, fatigue and sometimes diarrhea and vomiting. Most people will only get mildly ill from the flu and won’t need medical care or antiviral drugs, says Bert Kelly, a spokesman for the CDC. But one person’s mild case of the flu can turn into another person’s serious illness. That’s why the CDC asks that anyone with the flu stay home, refrain from travel and avoid contact with other people except to get medical care.
These instructions might seem obvious, but in a recent consumer poll of more than 2,000 CVS customers, two-thirds of respondents said they’d go to work with the flu, because they don’t like to use paid time off or because their bosses expect them to work through sickness. Respondents also said flu symptoms wouldn’t prevent them from going to the grocery store (28 percent), picking up children at school (12 percent) or taking public transportation (10 percent).
Why flu vaccines change every year
Influenza viruses mutate constantly, which is why vaccines need to be updated. Each year, researchers figure out the strains by analyzing data collected from early cases of the flu in a worldwide surveillance network. Once the virus is isolated in patients, doctors conduct testing to determine the virus subtype. CDC research suggests that H1N1 (the flu strain behind the 2009 pandemic), H3N2 and two main lineages of the B virus will be responsible for the 2018–2019 flu season.
The next step entails even further testing to understand the composition of the major viruses circulating among flu-infected people. Once researchers have a best guess of the strains most likely to spread, they develop vaccines anywhere from three to six months in advance of flu season.
How the vaccine protects you (and everyone else)
It takes about two weeks for the flu vaccine to take effect. During that time, the body develops antibodies to fight the virus. Some people are more sensitive to the flu shot and might experience mild flu-like symptoms afterward, but the flu shot will not give you the flu. In addition, some people might experience soreness at the injection site, but it only lasts a day or two.
The CDC estimates that flu vaccines are about 30 percent to 60 percent effective in any given year. That might sound low, but there’s something else at play: herd immunity. Populations can collectively stop flu transmission if enough people are immune to infection.
“The definition of ‘enough,’ that magic number, is based on how transmissible the infection is,” said Stephen S. Morse, an epidemiologist at the Mailman School of Public Health at Columbia University. “There are some standard ways to model this mathematically.”
A 50-percent vaccination rate would be enough to stop flu transmission in a geographic area. By contrast, it would take a 95-percent vaccination rate to build herd immunity to measles, which is about 10 times as transmissible as the flu.
“Even if a vaccine is only partially effective,” Morse said, “it will still reduce transmission significantly, as well as protecting you.”
Plus, if you do contract a strain of the flu despite being vaccinated, your symptoms will likely be more mild than if you hadn’t gotten one.
Does everyone get the same flu shot?
Most but not all flu vaccines are administered via injection. The reasons to get a particular type primarily come down to age and health status. It’s not your responsibility to choose the right flu vaccine; doctors, nurses, pharmacists and anyone else administering vaccines should collect enough information from you to make a selection on your behalf.
Here are four commonly available vaccines:
- Standard-dose flu shot (IIV): the traditional “flu shot,” an injected vaccine made from an inactivated (i.e., killed) flu virus; a number of manufacturers produce standard-dose flu shots, some of which are trivalent vaccines, meaning those that protect against three strains of the flu, while others are quadrivalent vaccines, which protect against four flu strains.
- High-dose flu shot: an injected, high-dose trivalent vaccine
- Egg-free flu shot (RIV): an injected quadrivalent vaccine made from recombinant DNA
- Nasal spray (LAIV): a nasal spray quadrivalent vaccine made from a live, weakened virus
Who gets which vaccines?
Many people can receive multiple types and brands of flu vaccine, and the CDC says there’s no reason to seek out one vaccine over another. “Not all products are likely to be uniformly available in any practice setting or locality,” according to the CDC’s 2018–2019 flu season report. “Vaccination should not be delayed in order to obtain a specific product when an appropriate one is already available.” In other words, get whichever appropriate vaccine is offered where you get vaccinated, without worrying about brand names or whether you’re receiving a trivalent or quadrivalent vaccine.
With that said, age and health issues dictate which types are appropriate.
For nonpregnant people ages 2 to 49, the CDC now recommends the nasal spray vaccine in addition to standard-dose flu shots. The spray was unavailable for the past two years due to uncertainty over its effectiveness against the H1N1 virus, but a tweaked version is back in play. The American Academy of Pediatrics, on the other hand, still recommends a standard-dose shot for kids, unless they really can’t handle needles.
Starting at age 50, adults should get shots, not the spray. Adults 65 and older are advised to get the high-dose flu shot or, as an alternative, a standard dose of a relatively new, strong flu shot called Fluad, which is only approved for this age group. Either way, the CDC says that older adults should make sure to get vaccinated, even if only standard-dose shots are available.
The high-dose flu shot is also typically recommended for organ transplant patients.
Pregnant and nursing mothers should get vaccinated with the standard-dose shot rather than the nasal spray. The CDC also recommends shots over the spray for children taking aspirin for any reason and for people with compromised immune systems who’ve recently taken antiviral drugs.
People with egg allergies can safely get the egg-free shot. For those with milder egg allergies (nothing worse than hives), the egg-free shot may not be necessary. Check with your doctor and the CDC’s guidelines for more information.
Should anyone not get a flu vaccine?
The vast majority of people can (and should) get a flu vaccine. The CDC notes two exceptions:
- People with a history of severe allergic reaction to a flu vaccine or a vaccine component other than egg
- Some but not all people who’ve previously developed Guillain-Barré syndrome within six weeks after getting a flu vaccine
These two populations shouldn’t write off flu protection altogether. Doctors may opt to use preventive antiviral drugs instead. Aside from these specific instances, the CDC’s Kelly says that everyone over 6 months old should get the flu vaccine, particularly high-risk populations, including children younger than 5, adults 65 and older, pregnant women, residents of nursing homes or long-term care facilities, people with severe obesity, American Indians and Alaska Natives, and people who have certain medical conditions, such as chronic asthma or heart problems.
“If you have questions about which vaccine is best for you,” Kelly said, “talk to your doctor or other healthcare professional.”
How long is flu season?
Typically, flu “illness activity” starts ramping up in November. In 2017–2018, flu-caused illness peaked in January and February and continued through the end of March, making it the longest season in recent years. However, it’s possible to catch the flu as late as May.
So when should you get a flu shot?
The CDC’s standard recommendation is to get vaccinated by the end of October. Children between the ages of 6 months and 8 years old getting their first flu shot, however, are supposed to receive two vaccine doses at least four weeks apart, so they should get the first dose as soon as possible to fit in a second dose by the end of October. Kids in this age group who’ve received flu vaccines before only need one dose.
Flu shots generally become available around the first week of August, and Piedra says not to worry about getting vaccinated too early. As a rule, he says it makes sense to think of back-to-school season as a reminder.
“I think it’s better to get one a little too early than too late,” Morse said. “There isn’t solid evidence about when it’s best to get a flu shot, except that you definitely want to get it at least two weeks before you might be exposed to the flu.”
If you don’t get vaccinated by late October, don’t write it off for the season. Getting the vaccine in late winter will confer protection through spring, when the flu is still being passed around.
Where should you get vaccinated?
Primary care doctors generally administer flu shots in their offices, and many employers, schools and drug stores offer them as well. If you need help finding a shot spot, the CDC recommends vaccinefinder.org.
Is there any reason to fear the vaccine might run out?
There hasn’t been a serious shortage of the flu vaccine since 2003–2004. Today there are many more vaccine manufacturers, so there’s little chance we’ll run out this year.
How much does flu vaccination cost?
Vaccination costs range from nothing to $70, depending on the type of vaccine your doctor recommends and your insurance coverage. High-dose shots for the elderly tend to be the most expensive, but Medicare should cover them. Affordable Care Act health plans should cover flu vaccination without a co-pay, but check with your carrier. CVS, for example, offers shots for $41 for the standard dose and $67 for seniors.
The future of the flu shot
A study is underway to find out whether a topical cream that treats genital warts and skin cancer might be able to boost immune responses against the flu. If so, it could help stretch the supply of vaccines for H5N1 (avian flu) and allow more people to get vaccinated during an outbreak. Researchers are also working on the phase 2 clinical trial for an experimental universal flu vaccine.
It will take at least one to two years for either to be publicly available, but for medical professionals and public health officials, anything that will increase flu coverage is a positive step forward.
“There are always barriers to getting enough people vaccinated, and the need for an annual vaccination is one barrier,” Piedra said. “It would be nice if we could produce a longer duration of immunity.”
This story has been updated to reflect newly released CDC data for the 2017–2018 flu season.