Flu Shots: 10 Facts About Flu Shots

Influenza is a viral infection. More commonly called the flu, this disease’s symptoms range from mild to severe. The flu can cause hospitalization or even death for people who are already frail. The severity of the flu differs from year to year.

Healthy people can be infected by the influenza virus and transmit it to others. But young children, elderly people, pregnant women, and people with certain medical conditions are at greater risk of suffering serious complications from the flu.

The best way to reduce the risk of catching the flu and spreading it to others is to receive an annual flu vaccine. Vaccines are available either as an injection or nasal spray. When more people in a community get the flu vaccine, the illness spreads to fewer people, and the whole community enjoys stronger immunity. Some experts suggest wearing a mask and doing good handwashing to reduce the chance of exposure to the flu.

The flu vaccine stimulates the production of antibodies. Antibodies are proteins that provide immune defense against illness. It takes the body about two weeks to generate antibodies after receiving the flu vaccine. This means that during the two weeks after your flu vaccine, your body remains vulnerable to infection.

Every year the seasonal flu vaccine is tailor-made to protect against the particular flu strains that are currently circulating. For example, trivalent flu vaccines protect against two types of influenza A (H1N1 and H3N2) and one type of influenza B. Quadrivalent vaccines protect against these three types plus an additional strain of influenza B.

Everyone over 6 months old should get the flu shot, with rare exceptions detailed later in this article. Some people need it more than others. People who work with or around children or sick people should strongly consider getting annual flu vaccinations to help protect themselves and the vulnerable populations they work with.

Different types of flu vaccines are appropriate for different groups of people. A patient's age, health status, and allergies should all be taken into account when deciding what type of flu vaccine is appropriate.

People ages 2 to 49 who do not want the standard, injectable flu vaccine may opt for the nasal spray vaccine as long as they meet certain requirements.

Ideally, it is best to receive the flu vaccine as soon as it becomes available at the start of flu season. Flu outbreaks may begin as early as October and typically peak between December and February. The CDC has studied peak flu months. In about 40% of US flu seasons studied (between 1982 and 2018), February was the month with the highest percentage of influenza-positive test samples. Keep in mind that this can vary from community to community, and from year to year.

Vaccines are usually available between September and early November. Getting the vaccine is appropriate as long as the flu is circulating. Receiving the flu vaccine as early as possible or just prior to the beginning of flu season works best to help protect yourself and your community against influenza.

Flu vaccines are widely available at pharmacies, supermarkets, urgent care centers, clinics, doctors’ offices, and university health centers. Some employers and schools even offer flu vaccines onsite. You do not need to be under the regular care of a doctor or nurse to get a flu vaccine.

Yes. It is still possible to get the flu even though you got the flu vaccine first. This can be for a variety of reasons. For one, the vaccine’s effectiveness varies based on a person’s age and health status. Another reason is that the vaccine is only fully effective two weeks after vaccination, when your body has had time to develop immunity.

Another issue is that a new vaccine is developed every year. Every year, public health officials predict which flu strains will circulate. They manufacture the yearly vaccine to best protect against the anticipated strains. However, the strains that circulate do not always match the strains accounted for in the vaccine.

Vaccine effectiveness is highest when the strains in the vaccination match closely with the strains that are causing illness. But even in years when the flu vaccine is a poor match, vaccination stimulates the production of antibodies. This confers some protection against the circulating strains via a process called cross-protection. These antibodies will be enough to protect some people from getting the flu and will help protect others against dangerous complications of the flu.

Even if you do get sick after vaccination, several studies show that you are likely to get less sick than you normally would. Those vaccinated experience fewer hospitalizations from illness, and those who are hospitalized have shorter stays on average.

There are many flu vaccination benefits. The obvious and perhaps greatest benefit is that the flu vaccine helps protect you and those close to you from getting the flu. But the benefits don’t end there.

The flu vaccine also helps protect vulnerable populations in the community: infants, young children, elderly adults, and those with chronic health conditions. These especially vulnerable people risk serious complications from infection.

Vaccination also lessens the intensity of the illness if you do catch the flu. That’s why the flu vaccine helps protect against potentially serious complications of influenza.

If you have certain serious illnesses, flu vaccinations may be even more important. People with heart disease who get vaccinated are less likely to experience harmful cardiac events. And people with diabetes and chronic lung disease who are vaccinated spend less time in the hospital on average.

Can the flu vaccine give you the flu? No, it is not possible to get influenza from the flu vaccine. Injectable flu vaccines contain either inactivated viruses or no virus at all, and neither one is capable of making people sick.

However, the nasal spray flu vaccine does contain live, weakened (attenuated) viruses. It also cannot make people sick with the flu. The viruses used in the nasal vaccine are cold-adapted. This means they are designed to only infect cooler environments, such as the environment inside your nose. The viruses in the nasal vaccine are incapable of infecting warmer body areas like your lungs. While some people who receive the nasal spray do develop some symptoms, those symptoms are typically milder and last a shorter time than they do in cases of flu infection.

Possible side effects vary between the flu shot and the nasal vaccine. The most typical side effect of the shot involves a local skin reaction. The skin immediately surrounding the shot area may swell, ache, redden, and become tender. This reaction typically clears up in one to two days.

Did the Flu Shot Cause My Illness?

It’s not likely. Studies comparing people who took the flu shot with people who took a placebo showed no difference as far as who developed symptoms like fever, runny nose, and body aches. Some people who receive the shot have been or will be infected by a common cold virus or some other illness. Also, some people are infected with flu before the shot has become fully effective (two weeks after injection).

Side Effects of the Nasal Spray Flu Vaccine

The nasal spray flu vaccine may cause side effects different from the injection, including vomiting, fever, and headache, as well as common cold symptoms like runny nose and sore throat. When these occur, they are usually much less severe than comparable symptoms found during a flu infection.

Serious Side Effects

Allergic reactions are the most serious side effects of flu vaccination. They are very rare. Anaphylactic reactions can be fatal, but they can also be effectively treated. The CDC recommends flu shots even for those with known egg allergies, provided these patients are monitored following the injection.

The Centers for Disease Control and Prevention (CDC) recommends that everyone age 6 months and older be vaccinated annually against the flu; however, it also provides a few exceptions.

Flu Shot

These people should not receive a flu shot:

• Infants under 6 months old, who are too young.
• Anyone with severe, anaphylaxis-type allergies to the flu shot or any ingredients contained within the vaccine. Such ingredients include gelatin and antibiotics.

These people should talk to their doctor before getting a flu shot:

• Currently feeling sick
• Have a history of Guillain Barre syndrome (GBS).
• Have an egg allergy or are allergic to other ingredients contained within the vaccine. People with egg allergies can usually still receive a vaccine with additional safety measures.

Nasal Flu Vaccine

These people should not receive a nasal flu vaccine:

• Children under 2
• Adults over 50
• Pregnant women
• Children 2-17 taking aspirin or salicylate (caution; risk of Guillain-Barre Syndrome)
• People with weak immune systems, and those who care for them
• Children ages 2 to 4 with asthma
• People prone to severe allergic reactions (anaphylaxis) to any of the vaccine’s ingredients
• People recently on antiviral drugs for influenza
• Children taking the drug Humira should not receive this vaccine, as this drug can reduce a child’s immune response.

These people should talk to their doctor before getting the nasal vaccine:

• People over age 5 with asthma
• People with serious chronic conditions, such as heart disease, kidney disease, and chronic lung diseases.
• Anyone currently ill to a moderate or severe degree (whether or not it’s due to fever)
• People who contracted Guillain Barre syndrome within 6 weeks following a previous flu vaccine.