Flu shot 101: Everything you need to know about getting vaccinated

Flu shot vs. nasal spray vaccine | Who needs it | When to get flu shot | Where to get flu shot | Cost | Vaccine safety | Efficacy

Winter is coming, and so is the dreaded flu season. Fortunately, there’s a vaccine for that—one that can help you, your family, and vulnerable or high-risk populations in the community avoid the influenza virus and the serious complications that can come along with it.

Maybe you get your flu shot every year. Or maybe it’s your first time considering one and you’re wondering whether it’s safe, effective, and necessary. Either way, it is important to understand what the flu shot is and the ramifications of skipping the seasonal flu vaccine. We called on experts to answer eight common flu shot questions.

1. What is the flu shot?

The flu vaccine is a once-a-year immunization that offers protection against whichever influenza strains experts predict will be circulating in a given year. 

“The flu [vaccine] is our best defense against the influenza virus,” says Ian Nelligan, MD, a primary care doctor at Stanford Hospital and Clinic in Palo Alto, California. “Beyond hand hygiene and contact precautions, it is really the best way to protect ourselves against infection.”

If you do catch the virus, flu symptoms include fever, chills, body aches, cough, and sore throat (to name a few). Serious complications can range from bronchitis and pneumonia to encephalitis (swelling of the brain), sepsis (life-threatening response to infection), and multi-organ failure.

These risks are why it’s important to get the injection… or nasal spray. The vaccine is available in both forms.

The shot

The flu shot is typically administered via an injection into the deltoid muscle of the shoulder. Despite common misconceptions, the shot does not contain live flu virus, explains Shital Patel, MD, an infectious disease specialist and investigator at the Baylor College of Medicine’s vaccine research center in Houston, Texas. Instead, it contains virus proteins that prompt an immune response in the body. 

Because the types of flu viruses change slightly each year, the flu shot changes each year as well, explains Dr. Patel. She says the World Health Organization (WHO), the Food and Drug Administration (FDA), and many other research groups are constantly examining all circulating strains of the flu viruses to make sure they develop the closest match for any given flu season. 

Some flu vaccines, she says, are trivalent, meaning they offer protection from three strains of influenza. Others are quadrivalent, meaning they offer protection from four influenza strains. Whether you get the quadrivalent or the trivalent vaccine largely depends on where you choose to receive your influenza vaccination, Dr. Patel says. In other words, some clinics and pharmacies carry trivalent vaccines; others carry quadrivalent. 

Dr. Patel encourages people to find a clinic or pharmacy that offers quadrivalent flu vaccines if it is convenient to do so, since it offers the “best possible option to protect yourself.”

For the 65+ population, Dr. Patel recommends a high-dose flu vaccine. Though it is trivalent, the high-dose vaccine contains four times the virus proteins that are in standard-dose flu shots, offering greater protection to seniors (who, based on age alone, face a higher risk of serious complications from the flu). The flu shot can be especially important for those who live in nursing homes where viruses can spread quickly.

For now the high-dose vaccine is only licensed for use in older adults ages 65 years and older. Everyone else should stick to the standard flu vaccine, Dr. Patel says. 

Some popular brand-name flu shots include Flublok, Fluarix, and FLUAD.

Nasal spray

A nasal spray version is also available for those who qualify to receive it. Because it is a live attenuated virus—aka a weakened version of the influenza virus—people with certain medical conditions and compromised immune systems (such as pregnant women, the elderly, people going through cancer treatment, or those living with organ transplants) should not receive the nasal spray flu vaccine. 

Otherwise, healthy individuals between the ages of 2 and 49 are eligible for the nasal spray flu vaccine as long as their healthcare professional approves. 

Unlike the flu shot, the nasal spray vaccine is quadrivalent by default. 

2. Do I need a flu shot?

Dr. Nelligan, who sees patients of all ages in his clinic, says it is important for everyone over 6 months of age to be vaccinated. Babies under 6 months cannot be vaccinated because their immune systems are too weak to respond to the vaccine. 

“Even in normal healthy adults, the flu can cause severe illness,” he says. So, yes, even if you have never had the flu and are in excellent health, you still need to make it a priority to get your flu vaccine.

Flu shots are particularly important for pregnant women because the flu can be quite dangerous to both the mother and the baby, agree Dr. Patel and Dr. Nelligan. The flu shot, on the other hand, is perfectly safe. In fact, a flu shot received in pregnancy continues to protect the baby after birth. 

Aside from babies under 6 months, the only people who should not get a flu shot are those who have had a severe allergic reaction to it in the past, Dr. Patel says. However, she also points out that such reactions are extremely rare. The risk of experiencing serious flu-related complications is much greater. In the 2019-2020 flu season, for example, the flu was responsible for up to 56 million illnesses and 740,000 hospitalizations according to the Centers for Disease Control and Prevention (CDC). 

3. When should I get a flu shot?

The flu doesn’t peak until mid-winter, but, in order to reap the full benefits of a flu shot, you need to get your immunization well before the flu virus becomes widespread, says Dr. Patel. The timing depends on where you live and can vary year-to-year, but the consensus is sooner rather than later. 

In general, flu season begins in the fall and lasts through early- to mid-spring (check the CDC’s influenza activity update page for information on flu activity in your area). Young children aged 6 months to 8 years old who are receiving the flu shot for the first time should have two doses, one month apart, says Dr. Patel. 

Many retail pharmacies start offering the flu shot as early as August. Medical clinics tend to receive their stock a little later, usually by the end of September. Dr. Nelligan encourages patients to get an influenza vaccine as soon as it’s available. Preferably, you should get the vaccine by the end of October so “you are covered before the flu is really starting to be transmitted in your area,” he says.

But, if you don’t make the end of October deadline, don’t let that keep you from getting it all. “If someone does not get their flu vaccine by the end of October, it is still beneficial to get vaccinated throughout the flu season,” Dr. Patel says. 

Another reason to get your flu shot ASAP? To safeguard yourself in the unlikely event of a vaccine shortage. Manufacturing and shipping issues led to a vaccine shortage in 2004, leading the CDC and other organizations to prioritize influenza vaccinations for high-risk groups over the general population. And while this sort of problem isn’t anticipated this flu season, it’s always better to be prepared. 

The only reason you might want to delay getting a shot is if you have a fever. The shot might “confuse” your immune system, leading to a less robust response to the vaccine. But as soon as the fever is gone, you should be ready to roll up your sleeves and get your shot. Regardless of when you get your flu vaccination, be aware that it takes two full weeks for its protective benefits to completely kick in, both Drs. Patel and Nelligan agree. 

4. Where should I go for the flu shot?

The flu vaccine is available at numerous locations. Most people get vaccinated at their doctor’s office or a pharmacy. Some employers offer flu shot clinics in the office, as do certain government agencies and campus health centers. There is even a Vaccine Finder map that will direct you to places offering the flu vaccine (and other vaccines) in your area. 

While it doesn’t really matter where you go, it could be good to visit your primary healthcare provider. “That is the person who knows your health conditions and history the best, and if the patient has any questions or concerns, that is probably the person who can answer those questions the best,” Dr. Nelligan says. “But if it becomes an issue of convenience or whether or not you are going to get it at all, I think getting it at the most convenient location is okay.”

RELATED: What you should know about getting vaccinated at the pharmacy

5. How much is a flu shot?

In terms of cost, insurance (including Medicare, Medicaid, private insurance companies, and health marketplace plans) should cover your flu shot. However, you might have to receive your influenza vaccination at a particular location—so be sure to check before heading in. 

Furthermore, many organizations offer free flu-shot clinics throughout the season for those who lack insurance or accessibility. If you do wind up needing to pay out of pocket for your flu shot, be aware that price varies depending on where you get it. 

If you’re unsure which flu shot you need, you can take our discount card to most major pharmacies and your pharmacist will find the best savings for you.

6. Is the flu shot safe?

The flu vaccine is safe for just about everyone. 

“Flu vaccines have been around for decades and safety has continued to be monitored throughout each season,” Dr. Patel says. “We have millions of data points [that say] it is safe.” She adds that in the 2018-2019 flu season 169 million doses of the flu vaccine were distributed with “no signal of any major effect or issues.”

Furthermore, you absolutely cannot get the flu from the flu shot, she says. Some individuals may experience mild to moderate flu-like symptoms, such as mild pain and soreness at the injection site, fatigue, headache, muscle aches, and/or low-grade fever—but this is not the flu and the side effects are unlikely to prevent you from going about your daily routine. Your body is simply mounting an immune response to the vaccine, she explains. “Your immune system is being stimulated to protect itself,” she says. 

Another common concern about the flu shot? Egg allergies. Most flu vaccines are cultured in egg protein, which means there is the potential for trace amounts of egg protein in the vaccine itself. Fortunately, flu shots are safe for people who are allergic to eggs, Dr. Patel says. 

“What we have found is that (most) people with egg allergies can receive any of the licensed, age-appropriate flu vaccines that are available right now,” she says.

The exception would be people with severe egg allergies, e.g., the type of allergy that leads to anaphylaxis. For this group, she recommends asking for the recombinant flu vaccine, which is not produced with chicken eggs.

Other allergies to the flu shot are extremely rare, she says. Anyone with concerns, however, should receive the flu vaccine in a medical setting.

7. How effective is the flu shot? 

So all that said, will receiving the flu shot guarantee that you won’t get the flu? No, the vaccine effectiveness isn’t infallible. But if you do get sick, the chances of severe illness or flu-related complications are significantly reduced, Dr. Patel explains. According to the CDC, the flu vaccine reduces the risk of flu illness by 40% to 60%. 

“Sometimes people think the flu vaccine will protect people 100%, but … how well the flu vaccine works depends on many different factors, and that changes from year to year,” she says. “But when we look at people who have been in the hospital, those who have had complications from the flu are those who have not been vaccinated.”

When it comes to the flu, the numbers speak for themselves. Throughout the 2017-2018 flu season, considered a “high-severity” season, around 80,000 adults and 81 (primarily unvaccinated) children died from flu-related complications. Close to 900,000 more were hospitalized, according to the National Foundation for Infectious Disease, and as mentioned earlier, the flu is responsible for millions of illnesses each year in the United States. 

“Those are big numbers, and if we can prevent [the flu], it reduces days off work, sick days, complications, and it reduces a significant burden on the individual and the family,” Dr. Patel says. “It is a preventable illness, and we have [the means] to prevent serious complications in children and those who are elderly who have a really hard time with it.”

RELATED: Does the flu shot prevent COVID-19?

8. How long does a flu shot last?

The immunity provided by a flu shot declines over time, which is part of the reason you need a flu shot each year. (The other part is that the active strains change every year.) While there’s not an exact length of time the flu shot lasts, experts say it protects you for around six months.