Flu Vaccine

Why the Flu Vaccine Matters

How effective is the flu vaccine?

Vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine and the strain or strains that circulate during the influenza season. Vaccine strains must be chosen 9 to 10 months before the influenza season, and sometimes mutations occur in the circulating strains of viruses between the time vaccine strains are chosen and the next influenza season. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine effectiveness.

Vaccine effectiveness also varies from one person to another, depending on factors such as age and overall health.

What are the side effects of the flu vaccine?

The most serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs. For this reason, people who have an allergy to eggs should not receive the influenza vaccine.

The National Center for Infectious Diseases (a division of the Centers for Disease Control and Prevention, CDC) says that influenza vaccine causes no side effects in most people who are not allergic to eggs. Less than one-third of people who receive the vaccine experience some soreness at the vaccination site, and about 5 to 10 percent experience mild side effects, such as headache or low-grade fever for about a day after receiving the vaccination.

Because these mild side effects mimic some influenza symptoms, some people believe the influenza vaccine causes them to get influenza. However, according to the CDC, "influenza vaccine produced in the United States has never been capable of causing influenza because the only type of influenza vaccine that has been licensed in the United States to the present time is made from killed influenza viruses, which cannot cause infection."

Who should immunize against the flu?

The flu causes complications that may develop into a more serious disease or become dangerous to some groups, such as elderly people and those with chronic medical conditions. For these reasons, the CDC recommends that the following groups immunize themselves each year. Always consult your physician for more information regarding who should receive the flu vaccine:

  • persons 50 years old or older (Vaccine effectiveness may be lower for elderly persons, but it can significantly reduce their chances of serious illness or death from influenza.)
  • children and adolescents six months to 19 years of age
  • residents of nursing homes and any other chronic care facilities that house persons of any age who have chronic medical conditions
  • adults and children who have chronic disorders of the pulmonary or cardiovascular systems, including children with asthma
  • adults and children who have the following medical conditions:chronic metabolic diseases (i.e., diabetes)
    • renal dysfunction
    • immunosuppression
    • hemoglobinopathies
  • children and teenagers (aged 6 months to 19 years) receiving long-term aspirin therapy
  • women who will be pregnant during flu season

In addition, the following groups should be vaccinated:

  • healthcare providers
  • employees of nursing homes and chronic care facilities who have contact with patients or residents
  • providers of home care to persons at high risk
  • household members (including children) of persons in high-risk groups
  • persons of any age who wish to decrease their chances of influenza infection, excluding persons who are allergic to eggs

When should I get a flu shot?

The Centers for Disease Control and Prevention (CDC) recommends getting the flu shot every year, between September and mid-November, before the flu season hits (usually December to April). The flu shot takes one to two weeks to become effective.

Although there are many new medications designed to treat flu symptoms and even shorten the duration of the illness, the flu vaccine still offers the best protection against the flu.

If I get the flu shot, can I still get the flu?

Every year, the flu shot "cocktail" changes to combat the current strains of influenza affecting the population. The World Health Organization (WHO) monitors flu outbreaks worldwide and recommends appropriate vaccine compositions to be used for the next year. However, sometimes, a strain may appear that was not included in the flu vaccine. People who have had the flu shot tend to have milder symptoms if they contract the flu.

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