Two facts should be emphasized before adverse reactions to influenza vaccine are discussed:
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Inactivated influenza vaccine contains non-infectious parts of killed viruses that cannot cause influenza;
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Coincidental respiratory disease unrelated to influenza vaccination can occur after vaccination.
Most people have little or no reaction to the vaccine. One in four might have a swollen, red, tender area where the vaccination was given. These local reactions typically are mild and rarely interfere with the person's ability to conduct usual daily activities.
In a much smaller number, fever, malaise, muscle ache, and other systemic symptoms can occur after vaccination with inactivated vaccine and most often affect persons who have had no prior exposure to the influenza virus antigens in the vaccine (e.g., young children). These reactions begin 6 – 12 hours after vaccination and can persist for 1 – 2 days. Young children may have chills or a headache, or feel a little sick. People who already have a respiratory disease may find their symptoms worsened. Usually none of these reactions lasts for more than a few days.
In addition, adverse reactions to the vaccine, perhaps allergic in nature, have been observed in some people. These could be due to an egg protein allergy because the egg in which the virus is grown cannot be completely extracted. These people should be vaccinated only if their doctor believes it necessary and if the vaccine is given under close observation by a doctor.
