Everything You Need to Know About the Flu Shot

As the temperature outside inches toward freezing, we must start preparing for winter. We prepare our houses by turning up the thermostat, unpacking the blankets and sweaters, and trimming back our gardens for winter dormancy. We prepare our cars by creating emergency kits, keeping fuel levels high, and replacing the antifreeze. It's important to also prepare our bodies for the onset of flu season.

What is the flu shot and how does it work?

The flu shot is a vaccine that protects against influenza. Vaccines are like training modules for your body's immune system. By introducing weaker or inactivated versions of viruses to your body, a vaccine allows your immune system to practice fighting the "infection" while it's not dangerous. Once your body clears out the vaccine, it creates memory cells that "remember" how to fight the infection if you ever contract it again. These memories are strong enough to stop a new infection even if the viruses are activated and stronger than they were when you were first inoculated.

The flu vaccine is composed of weakened or inactive versions of three or four different strains of influenza, depending on which vaccine type you get. The strains of influenza included are determined based on research and predictions of which types will be most common in any given year. Sometimes the predictions are correct and sometimes they are not. When they are correct, the vaccine leads to a decrease in influenza diagnoses and deaths.

There are three types of flu vaccine:

Inactivated influenza,
Recombinant influenza and
Live attenuated influenza.

The inactivated influenza vaccine is a vaccine that uses an inactive, or "dead," version of the virus. The recombinant influenza vaccine contains no traces of the influenza virus at all. The live attenuated influenza vaccine, or the nasal spray, contains a weakened version of influenza and is applied through your nose. The weakened virus is cold-adapted, meaning that it might survive in your nose, but it won't in your lungs.

When should you get the flu shot and how long does it last?

The best time to get your flu shot is by the end of October. If you haven't gotten your flu shot yet, don't worry. Peak flu season is between December and February, so if you go in November, you still have time for the vaccine to settle into your system before you're most at risk. It takes about two weeks after vaccination for the flu vaccine to begin to protect you.

Everyone 6 months or older, especially people at risk of serious complications from influenza, should get a flu shot. Your doctor can choose the appropriate type of vaccine for you. The Center for Disease Control has a list of people who should be prioritized when there is a flu vaccine shortage. This list is also useful to consult if you are wondering if you should get a flu shot. It includes:

Children 6 months to 4 years old;
People 50 years old and older;
People with chronic diseases, including lung disease, heart disease, and kidney, liver, neurologic, blood, or metabolic disorders;
People who are immunosuppressed;
Women who are or will be pregnant during flu season;
Children taking certain types of medications;
Residents of nursing homes and other chronic-care facilities;
American Indians/Alaska Natives;
People with extreme obesity;
Health care personnel;
Caregivers and family of children under five and adults aged 50 and older; and
Caregivers and family of people with certain medical conditions.

Immediately after getting the flu shot, you might experience soreness and redness in your arm. For a short period of time, you might also have side effects such as runny nose, wheezing, headache, vomiting, muscle aches, fever, sore throat, or coughing. The CDC reports that these side effects do not last long, and they are significantly weaker and shorter-lasting than the symptoms of the flu itself.

The flu shot is good for the year after you receive it. The CDC recommends that you get vaccinated every year, because the vaccine changes to meet the demands of that season. In some cases, the effects of getting vaccinated can carry over from year to year. However, that depends on the type of vaccine administered and the types of influenza virus that spread in subsequent years.

What are the benefits and risks of getting a flu shot?

There are many benefits of getting your flu shot. Among them:

It can prevent you from contracting the flu,
It can reduce the risk of influenza-related hospitalization,
It can prevent complications in people with chronic health conditions,
It can protect women during and after pregnancy,
It can be life-saving in children,
It can reduce the severity of influenza if you catch the virus anyway and
It can protect the people around you from contracting influenza.

Some people (children under six months old and people with life-threatening allergies to the ingredients of the vaccine) cannot get the flu shot. Just like other vaccines, herd immunity can help those people to avoid contracting the disease.

The CDC also recommends against giving the live attenuated influenza vaccine to certain vulnerable groups of people. These people can still benefit from other types of the vaccine. And if you have an allergic reaction to the vaccine, you can receive compensation form the Health Resources & Services Administration's National Vaccine Injury Compensation Program.

The flu shot will not give you influenza. The vaccine is also not infectious to the people around you while your body is working to get rid of it. The inactivated virus is a "dead" virus; it will not multiply in your system, and it is not infectious. The recombinant vaccine is made with no virus at all, but still provides immunity to certain strains of the flu.

It is possible to get the flu even after you've received the flu shot. This is because of how the vaccine is made. There are several types of influenza that could circulate in any season. The vaccine only protects against some of them. It also does not protect against similar illnesses like rhinovirus (the common cold) and respiratory syncytial virus (RSV). However, the vaccine can reduce the severity of illness if you do get the flu. In fact, vaccination in children can significantly reduce a child's risk of dying from the flu.

Are flu shots effective?

Flu vaccines reduce the risk of flu illness by 40%–60%. Several factors affect the effectiveness of the vaccine, including:

The characteristics of the person,
What influenza viruses are circulating that year and
Which type of vaccine was used.

Effectiveness of the flu vaccine depends on the similarity between the vaccine administered and the flu virus that is common in any given year.

The history of the flu vaccine

The theory of vaccination was first introduced by Edward Jenner in 1798. It was based on the observation that people who had survived smallpox were later immune to it, and that a similar disease, cowpox, could protect children from the disease without putting them at risk of infection. Louis Pasteur developed the first live attenuated bacterial vaccine in 1879 and the first live attenuated viral vaccine in 1884.

The United States has experienced several influenza pandemics, most notably the 1918 "Spanish" influenza. Five hundred million people worldwide were infected with the "Spanish" influenza, prompting the United States government to invest in the creation of a flu vaccine. In 1942, the first Influenza A/B vaccine was introduced to the armed forces. It was licensed in 1945 and later used for civilians. The United States experienced other influenza pandemics throughout the twentieth and twenty-first centuries. Each strain of influenza saw a reduced rate of infection and death compared to the pandemics before them. In the United States:

1918 "Spanish" influenza: 675,000 deaths
1957–8 "Asian" influenza (H2N2): 116,000 deaths.
1968–9 "Hong Kong" influenza (H3N2): 100,000 deaths.
2009 Swine flu (H1N1): 12,469 deaths.

After the use of vaccines against influenza became common, pandemics such as these continued to occur because the vaccines created for those years were unable to meet the demand of the season. For example, 2009's swine flu (H1N1) contained a unique combination of influenza genes that scientists had never identified before. After that first year, a vaccine was created to respond to H1N1 in subsequent years.

In 2003, the live attenuated influenza vaccine (nasal spray) was approved, with questions regarding its effectiveness arising in 2017 and affecting its availability. The inactivated and recombinant vaccines were still available for inoculation.

According to Vox, 80,000 Americans died of the flu last year. (The CDC notes that these numbers are a rough estimate.) Your health insurance is required to pay for the flu shot and other vaccines, although they might restrict where you can go for your shot. So, even if you're skeptical about the effectiveness of the vaccine, the risk of getting it pales in comparison to the risks of contracting the flu. You can get your flu shot at most pharmacies and clinics. The CDC provides a tool to find flu shot providers near you. In the meantime, protect yourself further after you get your flu shot, by covering your coughs, washing your hands often, and avoiding people who are sick.

This information is based on research from the CDC, and each individual should consult with a doctor as to whether they should or not get the flu shot.