Flu Vaccines and How They Work

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Flu SHot, Vaccination

By Dr. Mary O’Brien MD

Composed of two type A viruses and one type B virus, seasonal flu vaccines change annually to reflect the viral types and strains that international surveillance and scientific analysis predict will circulate during a given year. Each vaccine’s protective potential is determined by individual health status and by similarities among the viruses contained in the vaccine and those in circulation. A vaccine that closely matches circulating viruses protects most people from serious flu-related illness.
Even a vaccine that is not a close match affords a degree of protection. Flu vaccines do not protect against flu-like illnesses, which are caused by non-influenza viruses. Also, seasonal flu vaccine does not provide protection against type C influenza.
Seasonal flu vaccine is available in two forms: injected and intranasal routes. Injected vaccine is made from inactivated viruses while the intranasal is an live-attenuated virus.

Live-attenuated influenza vaccine (LAIV) is a flu vaccine in the form of a nasal spray. LAIV is made from live, weakened viruses that do not cause the flu. The Center for Disease Control has approved LAIV for use in people between two years and 49 years of age who are healthy and who are not pregnant. LAIV is also an approved option for people who live with or care for those at high risk for contracting flu. It is not recommended for caregivers of people whose severely compromised immune systems require a protected environment. These healthy individuals should get the flu shot.

Flu vaccinations may be given at the same time that other vaccines are administered. Although vaccination is advisable as soon as seasonal vaccines become available, being vaccinated later in the flu season, like December, still confers benefit in most years. One dose of vaccine a year is sufficient for most people. Children under nine years of age who are being vaccinated against flu for the first time or who were initially vaccinated with a single dose during the previous flu season should receive two doses of vaccine at least four weeks apart.

Side effects associated with flu shots are generally mild, appear shortly after the injection, and persist for a day or two. They include soreness: redness; and swelling at the injection site; low-grade fever; sore or red eyes; and aches. LAIV can cause headache and runny nose. Adults may also develop sore throat or a cough, and children may wheeze, vomit, and have muscle aches or fever.

Symptoms of rare, serious reactions include:

  • high fever
  • behavioral changes
  • breathing difficulties
  • hoarseness or wheezing
  • hives
  • paleness
  • weakness
  • rapid heartbeat
  • dizziness

Although flu-related morbidity and mortality vary from year to year, the CDC estimates that between five and 20 percent of Americans contract flu in a given year and that 200,000 are hospitalized for treatment of flu-related complications. Approximately 36,000 deaths a year result from flu-related causes in the United States. Always check with your doctor before getting a flu vaccination. Also, many local pharmacies offer flu vaccinations in the store to fit your schedule.

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