Addressing misconceptions about flu vaccines

People should get a flu vaccine every year for optimal protection against flu

CDC recommends a yearly flu vaccine for everyone 6 months and older with rare exception. The reason for this is that a person’s immune protection from vaccination declines over time, so an annual vaccination is needed to get the “optimal” or best protection against the flu. Additionally, flu viruses are constantly changing, so the vaccine composition is reviewed each year and updated as needed.

Getting a flu vaccine will not give you flu

Flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are made with either inactivated (killed) viruses, or with only a single protein from an influenza virus. The nasal spray vaccine contains live viruses that are attenuated (weakened) so that they will not cause illness.

Flu illness can be serious

Flu can be a serious disease, particularly among young children, older adults, and people with certain chronic health conditions, such as asthma, heart disease or diabetes. Any influenza virus infection can carry a risk of serious complications, hospitalization or death, even among otherwise healthy children and adults. Therefore, getting vaccinated is a safer choice than risking illness to obtain immune protection.

Preferential recommendation for older adults

There are three influenza vaccines that are preferentially recommended for people 65 years and older.

Flu vaccine side effects and adverse events

Most side effects following flu vaccination are mild

Some people report having mild side effects after flu vaccination. The most common side effects from flu shots are soreness, redness, tenderness or swelling where the shot was given. Low-grade fever, headache and muscle aches also may occur. If these reactions occur, they usually begin soon after vaccination and last 1-2 days.

Side effects from the nasal spray flu vaccine may include: runny nose, wheezing, headache, vomiting, muscle aches, fever, sore throat and cough. If these problems occur, they usually begin soon after vaccination and are mild and short-lived. The most common reactions people have to flu vaccines are considerably less severe than the symptoms caused by actual flu illness.

Serious side effects from flu vaccination are very rare

Serious allergic reactions to flu vaccines are very rare. If they do occur, it is usually within a few minutes to a few hours after vaccination. While these reactions can be life-threatening, effective treatments are available.

Getting a flu vaccine and still getting sick with flu symptoms

There are several reasons why someone might get flu symptoms even after they have been vaccinated against flu.

• Someone can get sick with another respiratory virus besides influenza virus, such as rhinoviruses or SARS-CoV-2 (the virus that causes COVID-19). Other respiratory viruses can cause symptoms similar to flu, and they can also spread and cause illness during flu season. Flu vaccines only protect against flu, not other illnesses.
• Someone can be exposed to influenza viruses shortly before getting vaccinated or during the two-week period after vaccination that it takes the body to develop immune protection. This exposure may result in a person becoming sick with flu before protection from vaccination takes effect.
• Flu vaccines vary in how well they work. Someone can get vaccinated but still get sick with flu. However, flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
• There are also many different influenza viruses that spread and cause illness among people, so someone can get vaccinated and still get sick if they are exposed to an influenza virus that is very different from the viruses in the flu vaccine. The ability of a flu vaccine to protect a person depends partially on the similarity or "match" between the vaccine viruses chosen to make vaccine and those spreading and causing illness. Even when that happens though, flu vaccination can still reduce severity of illness.

Flu vaccination and other respiratory viruses

Flu vaccines are not thought to make people more susceptible to other respiratory infections.

A 2012 study that suggested that flu vaccination might make people more susceptible to other respiratory infections. After that study was published, many experts looked into this issue further and conducted additional studies to see if the findings could be replicated. No other studies have found this effect. It's not clear why this finding was detected in the one study, but the majority of evidence suggests that this is not a common or regular occurrence and that flu vaccination does not, in fact, make people more susceptible to other respiratory infections.

Flu vaccination and COVID-19

There is no evidence that getting a flu vaccination increases your risk of getting sick from a coronavirus, like the one that causes COVID-19.

You may have heard about a study published in January 2020 that reported an association between flu vaccination and risk of four commonly circulating seasonal coronaviruses, but not the one that causes COVID-19. This report was later found to be incorrect.

The results from that initial study led researchers in Canada to look at their data to see if they could find similar results in their population. The results from this study showed that flu vaccination did not increase risk for these seasonal coronaviruses. The Canadian findings highlighted the protective benefits of flu vaccination.

The Canadian researchers also identified a flaw in the methods of the first study, noting that it violated the part of study design that compares vaccination rates among patients with and without flu (test negative design). This flaw led to the incorrect association between flu vaccination and seasonal coronavirus risk. When these researchers reexamined data from the first study using correct methods, they found that flu vaccination did not increase risk for infection with other respiratory viruses, including seasonal coronaviruses.

Misconceptions about whether flu vaccines work

Flu vaccine effectiveness can vary. The protection provided by a flu vaccine varies from season to season and depends in part on the age and health status of the person getting the vaccine and the similarity or "match" between the viruses in the vaccine and those in circulation. During years when the flu vaccine match is good, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness and complications. However, the benefits of flu vaccination will still vary, depending on characteristics of the person being vaccinated (for example, their health and age), what influenza viruses are circulating that season and, potentially, which type of flu vaccine was used.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.

In adults, studies have not shown a benefit from getting more than one dose of vaccine during the same flu season, even among elderly persons with weakened immune systems. Except for children getting vaccinated for the first time, only one dose of flu vaccine is recommended each season.

Misconceptions about the timing of seasonal flu vaccination

While delaying getting a flu vaccine until later in the fall may lead to higher levels of immunity during winter months, this should be balanced against possible risks, such as missed opportunities to receive vaccine and difficulties associated with vaccinating a large number of people within a shorter time period.

Vaccination can still be beneficial as long as influenza viruses are circulating. If you have not been vaccinated by the end of November, it can still be protective to get vaccinated in December or later. Flu is unpredictable and seasons can vary. Seasonal flu disease usually peaks between December and March most years, but disease can occur as late as May.

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Misconceptions about physician consent for vaccination

There is no recommendation for pregnant people or people with pre-existing medical conditions to seek special permission or secure written consent from their doctor for vaccination if they get vaccinated at a worksite clinic, pharmacy or other location outside of their physician's office. With rare exception, CDC recommends an annual flu vaccine for everyone 6 months and older, including pregnant people and people with underlying medical conditions.

Misconceptions about “stomach flu”

Many people use the term “stomach flu” to describe illnesses with nausea, vomiting or diarrhea. These symptoms can be caused by many different viruses, bacteria or even parasites. While vomiting, diarrhea, and being nauseated or “sick to your stomach” can sometimes be related to flu — more commonly in children than adults — these problems are rarely the main symptoms of influenza. Flu is a respiratory disease and not a stomach or intestinal disease.