How to respond to flu vaccine doubters

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The benefits of influenza vaccination are clear to those in the medical community. Yet misinformation and unfounded fears continue to discourage some people from getting a flu shot. During the 2018–2019 influenza season, only 45% of US adults and 63% of children were vaccinated.1

Table 1. Reasons people give for not wanting the influenza vaccine, and potential responses
What should we tell patients who say no to the flu shot? Here are 12 reasons people give for not wanting to receive the inactivated influenza vaccine, along with some potential responses and comments about the nasal live-attenuated vaccine (Table 1).


Multiple studies have shown that the flu vaccine prevents millions of flu cases and flu-related doctor’s visits each year. During the 2016–2017 flu season, flu vaccine prevented an estimated 5.3 million influenza cases, 2.6 million influenza-associated medical visits, and 85,000 influenza-associated hospitalizations.2

Several viral and host factors affect vaccine effectiveness. In seasons when the vaccine viruses have matched circulating strains, flu vaccine has been shown to reduce the following:

  • The risk of having to go to the doctor with flu by 40% to 60%
  • Children’s risk of flu-related death and intensive care unit (ICU) admission by 74%
  • The risk in adults of flu-associated hospitalizations by 40% and ICU admission by 82%
  • The rate of cardiac events in people with heart disease
  • Hospitalizations in people with diabetes or underlying chronic lung disease.3

In people hospitalized with influenza despite receiving the flu vaccine for the season, studies have shown that receiving the flu vaccine shortens the average duration of hospitalization, reduces the chance of ICU admission by 59%, shortens the duration of ICU stay by 4 days, and reduces deaths.3

Table 2. Contraindications and precautions to the use of influenza vaccines
Since 2010, the Advisory Committee on Immunization Practices (ACIP) of the US Centers for Disease Control and Prevention (CDC) has recommended routine annual influenza vaccination for all persons 6 months of age and older who do not have a contraindication to it.4Table 2 summarizes the current contraindications to and cautions regarding influenza vaccination.


Selecting an effective influenza vaccine is a challenge. Every year, the World Health Organization and the CDC decide on the influenza strains expected to circulate in the upcoming flu season in the Northern Hemisphere, based on data for circulating strains in the Southern Hemisphere. This decision takes place about 7 months before the expected onset of the flu season. Flu viruses may mutate between the time the decision is made and the time the vaccine is administered (as well as after the flu season starts). Also, vaccine production in eggs needs time, which is why this decision must be made several months ahead of the flu season.

Vaccine effectiveness varies by virus serotype. Vaccines are typically less effective against influenza A H3N2 viruses than against influenza A H1N1 and influenza B viruses. Effectiveness also varies from season to season depending on how close the vaccine serotypes match the circulating serotypes, but some effectiveness is retained even in seasons when some of the serotypes don’t match circulating viruses. For example, in the 2017–2018 season, when the influenza A H3N2 vaccine serotype did not match the circulating serotype, the overall effectiveness in preventing medically attended, laboratory-confirmed influenza virus infection was 36%.5

A universal flu vaccine that does not need to be updated annually is the ultimate solution, but according to the National Institute of Allergy and Infectious Diseases, such a vaccine is likely several years away.6


Pain at the injection site of a flu shot occurs in 10% to 65% of people, lasts less than 2 days, and does not usually interfere with daily activities.7

Systemic symptoms such as fever, malaise, and myalgia may occur in people who have had no previous exposure to the influenza virus antigens in the vaccine, particularly in children. In adults, the frequency of systemic symptoms after the flu shot is similar to that with placebo.

The Vaccine Adverse Event Reporting System, which has been capturing data since 1990, shows that the influenza vaccine accounted for 5.7% of people who developed malaise after receiving any vaccine.8

The injectable inactivated influenza vaccine cannot biologically cause an influenza virus-related illness, since the inactivated vaccine viruses can elicit a protective immune response but cannot replicate. The nasal live-attenuated flu vaccine can in theory cause acute illness in the person receiving it, but because it is cold-adapted, it multiplies only in the colder environment of the nasal epithelium, not in the lower airways where the temperature is higher. Consequently, the vaccine virus triggers immunity by multiplying in the nose, but doesn’t infect the lungs.

From 10% to 50% of people who receive the nasal live-attenuated vaccine develop runny nose, wheezing, headache, vomiting, muscle aches, fever, sore throat, or cough shortly after receiving the vaccine, but these symptoms are usually 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.

While influenza illness results in natural immunity to the specific viral serotype causing it, this illness results in hospitalization in 2% and is fatal in 0.16% of people. Influenza vaccine results in immunity to the serotypes included in the vaccine, and multiple studies have not found a causal relationship between vaccination and death.9

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