What is an Inactivated Influenza Vaccine?

An inactivated influenza vaccine contains strains of killed influenza viruses grown in chicken eggs, as opposed to the flu mist that has live viruses. The strains in the vaccine change annually to try and match the ones most likely to circulate and cause the flu. It is generally recommended that everyone over the age of six months get vaccinated against the flu, especially those considered to be high risk, although there are some cases in which the vaccine should not be received. It is rare to have serious complications from an inactivated influenza vaccine, but there are a few possible side effects.

Since the strains of influenza viruses that circulate can change frequently, scientists try to match the virus in the inactivated influenza vaccine to the strains most likely to circulate during flu season each year. The vaccine will typically contain three strains of killed influenza viruses, such as influenza A/H1N1, A/H3N2, and influenza B. It takes approximately two weeks after receiving the injection for the body to build protection by producing antibodies, and the protection lasts about a year. Getting an inactivated influenza vaccine cannot cause influenza because it does not contain live viruses.

Health officials generally recommend getting an inactivated influenza vaccine just prior to the start of the flu season, which is in the winter months for most countries. The vaccine is given by injection into the muscular area of the upper arm. Many locations offer flu vaccines, like doctor’s offices, health clinics, and pharmacies. Sometimes schools, churches, and senior centers will offer it as well.

The inactivated influenza vaccine is usually approved for those aged six months and older. Children under the age of nine might need two shots given one month apart, but those older than nine usually only need one per year. Doctors typically recommend that everyone get vaccinated each year, especially those who are at high risk for complications from the flu. High risk individuals include health care workers, those in close contact with children under six months old, pregnant women, and those over age 50. People who live in nursing homes or have chronic medical conditions might also be high risk.

There are some cases in which people should not receive an inactivated influenza vaccine. Those who have had severe allergic reactions to the vaccine or any of its components, or those who are allergic to chicken eggs should not get it. People who are moderately or severely ill should wait until they recover. Additionally, those who have ever had Guillain-Barre syndrome should consult a doctor prior to receiving an influenza vaccine.

Most people who get the inactivated influenza vaccine do not experience any complications, but there are a few side effects possible. The most common ones are soreness and swelling at the injection site. Less than 1% of people will have other side effects, including low-grade fever, cough, and aches. Side effects might begin shortly after getting the shot but will typically disappear within one to two days.

In rare instances, people might have an allergic reaction to the vaccine. Signs of a serious reaction include difficulty breathing, hives, fast heartbeat, and dizziness. When a reaction does occur, these symptoms usually happen within a few minutes of getting the shot.