Influenza Vaccine - Side Effects

Side Effects

Side effects of the flu vaccine injection include:

• mild soreness, redness, and swelling where the shot was given
• fever
• aches

These problems usually begin soon after the injection, and last 1–2 days.

Side effects of the activated/live/LAIV flu nasal spray vaccine:

Some children and adolescents 2–17 years of age have reported:

• runny nose, nasal congestion or cough
• fever
• headache and muscle aches
• wheezing
• abdominal pain or occasional vomiting or diarrhea

Some adults 18–49 years of age have reported:

• runny nose or nasal congestion
• sore throat
• cough, chills, tiredness/weakness
• headache

More severe, but very rare side effects include:

• life-threatening allergic reaction

Some injection-based flu vaccines intended for adults in the United States contain thiomersal (also known as thimerosal). Despite some controversy in the media, the World Health Organization (WHO) has concluded that there is no evidence of toxicity from thiomersal in vaccines and no reason on grounds of safety to change to more-expensive single-dose administration.

Although Guillain-Barré syndrome had been feared as a complication of vaccination, the CDC states that most studies on modern influenza vaccines have seen no link with Guillain-Barré.

A review has concluded that the 2009 H1N1 ("swine flu") vaccine has a safety profile similar to that of seasonal vaccine. Although one review gives an incidence of about one case per million vaccinations, a large study in China, reported in The New England Journal of Medicine covering close to 100 million doses of vaccine against the 2009 H1N1 "swine" flu found only eleven cases of Guillain-Barre syndrome, (0.1 per million doses) total incidence in persons vaccinated, actually lower than the normal rate of the disease in China, and no other notable side effects; "The risk-benefit ratio, which is what vaccines and everything in medicine is about, is overwhelmingly in favor of vaccination." Getting infected by influenza itself increases both the risk of death (up to 1 in 10,000) and increases the risk of developing Guillain-Barré syndrome to a much higher level than the highest level of suspected vaccine involvement (approx. 10 times higher by 2009 estimates).