Influenza Vaccine

Influenza, "the flu," is potentially a very serious illness that can affect people of any age. Each year 5% to 20% of the U.S. population gets the flu, and there averages over 200,000 hospitalizations and 36,000 deaths due to flu and its complications.

The most effective way to prevent the flu is with vaccination. Below is information adapted from the Centers For Disease Control website concerning whom should be vaccinated and frequently asked questions about the flu vaccines.

  • Whom to Vaccinate
  • Influenza Vaccine FAQ
  • Influenza Vaccine FAQ - Healthcare Workers

In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. In fact, the Advisory Committee on Immunization Practices (ACIP) now recommends that anyone over the age of 6 months be vaccinated annually. The ACIP continues to regard the following groups as priority groups to receive influenza vaccine:

  • Persons 50 years old or greater
  • Children/adolescents aged 6 months to 18 years (particularly those aged 6 months--4 years (59 months)).
  • Residents of nursing homes or other chronic care facilities
  • Adults or children with chronic respiratory or cardiac conditions including asthma (hypertension is not considered a high risk condition)
  • Adults or children who have required regular medical care in the preceding year for chronic metabolic disease such as diabetes, renal dysfunction, hemoglobinopathies, immunodeficiency (including immunodeficiency caused by medication or HIV)
  • Adults and children with any neurologic condition (e.g. spinal cord injury, seizure disorder, etc) that can compromise respiratory function
  • Children and adolescents (6 mos to 18 yrs) who are taking aspirin regularly
  • Women who will be pregnant during the influenza season
  • Persons who live with or care for persons at high risk for influenza-related complications, including healthy household contacts and caregivers of children aged 0-59 months
  • Healthcare workers

What is the flu shot?

The flu shot is an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. It contains three (or four in case of quadrivalent vaccine) influenza viruses. The vaccine strains – one A (H3N2) virus, one A (H1N1) virus, and one (or two) B virus – are representative of the influenza vaccine strains anticipated to be circulating that year. Viruses for the flu shot are grown in eggs. About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.

Is the flu shot safe?

Because the viruses in the flu shot are killed (inactivated), one cannot get the flu from a flu shot. The risk of a flu shot causing serious harm, or death, is extremely small. However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions. Almost all people who get influenza vaccine have no serious problems from it. What are the side effects that could occur?

  • Soreness, redness, or swelling where the shot was given
  • Fever (low grade)
  • Aches
If these problems occur, they begin soon after the shot and usually last one to two days.

Who should not get a flu shot?

Persons who have ever had a severe allergic reaction to eggs or to a previous flu shot should not have a flu shot. Persons who have history of Guillain Barre Syndrome should consult with their doctor before receiving a flu shot.

How effective is the flu shot?

With the flu shot, when the "match" between vaccine and circulating strains is close, the vaccine prevents influenza in about 70%-90% of healthy persons younger than age 65 years. Among elderly persons and those with chronic medical conditions (asthma, diabetes, heart disease, etc) the flu shot is less effective in preventing influenza but is effective in preventing a significant proportion of the complications of influenza such as pneumonia necessitating hospitalization and death.

Why is it necessary to get a flu shot every year?

Flu viruses change from year to year, which means two things. First, one can get the flu more than once during a lifetime. The immunity (natural protection that develops against a disease after a person has had that disease) that is built up from having the flu caused by one virus strain doesn't always provide protection when a new strain is circulating. Second, a vaccine made against flu viruses circulating last year may not protect against the newer viruses. That is why the influenza vaccine is updated to include current viruses every year. Another reason to get flu vaccine every year is that after vaccination, immunity to the disease declines over time and may be too low to provide protection after one year.

Why is it particularly important that healthcare workers be vaccinated against influenza (the flu)?

Healthcare workers infected with the flu can spread it to patients, a particularly vulnerable population because of co-morbid illness and often, advanced age. An infected healthcare worker can spread the infection even before he or she is clinically ill.

In some flu seasons the vaccine has been ineffective against circulating strains of influenza? Why should healthcare workers (or others) be expected to be vaccinated when sometimes the vaccine may be incompletely effective as it was in the 2007-2008 flu season?

The Centers for Disease Control (CDC) recommends getting a flu vaccination every year, even when there is a less than ideal match between the viruses used to make the vaccine and those causing illness. This is especially important for people at higher risk for serious flu-related complications and for people who come into close contact with them (i.e., healthcare workers). Flu viruses are always changing. Sometimes they change from when the vaccine is recommended and the beginning of the flu season; they can even change during a flu season. When flu viruses change, they may no longer closely match viruses used to make that season’s flu vaccine. This can make the vaccine less effective. But even when this happens, the vaccine can still offer protection:

  1. The vaccine contains three (or four) viruses, so it can provide protection against the other two (or three) viruses that may be making people sick.
  2. The immune protection derived from the vaccine can provide partial protection against flu viruses that are related to those used to make the vaccine (this is called cross-protection.) So while a less than ideal match can reduce vaccine benefit, the vaccine can still provide enough protection to make illness less severe and prevent flu-related complications.
A less than perfect vaccine is still the best protection we have against influenza. That is why CDC continues to recommend getting the vaccine even when there is a less than perfect match between viruses used to make the vaccine and viruses making a lot of people sick.

For persons who do not like injections are there alternative means of vaccination?

The answer that follows is for historical purposes only as Live Attenuated Influenza Vaccine in not recommended for the 2016-2017 flu season. LAIV may or may not be available for subsequent flu seasons.

Yes. Vaccination with a nasal-spray flu vaccine (Live Attenuated Influenza Vaccine (LAIV)) is an option for healthy persons aged 2-49 years who are not pregnant. This vaccine has been shown to be highly effective in preventing influenza in children and in preventing influenza like illness in adults. It can be made available as an option for employees who would prefer to not receive an injection. It is contraindicated in persons aged 50 or greater, those with certain chronic medical conditions putting them at high risk of complications from influenza, those with history of egg allergy, and those with prior Guillain Barre Syndrome. The nasal spray vaccine (LAIV) contains attenuated live virus. Rarely vaccine strain virus can be transmitted to close contacts of the person vaccinated. Because of its attenuated nature the vaccine strain of flu does not tend to cause clinical illness in those rare instances of transmission. The nasal-spray vaccine is approved for use in healthcare personnel except for those caring for the most immunocompromised patients (for example, those caring for hematopoietic stem cell transplant patients in a protective environment.

Influenza Primer