Are there any flu shot side effects in adults or in children?
Charles P. Davis, MD, PhD
Emergency Medicine, WebMD Medical Expert
Medical Editor/Author, MedicineNet
Although annual influenza (injectable) vaccination has long been recommended for people in the high-risk groups, many still do not receive the vaccine, often because of their concern about side effects. They mistakenly perceive influenza as merely a nuisance and believe that the vaccine causes unpleasant side effects or that it may even cause the flu. The truth is that influenza vaccine causes no side effects in most people. The most common and serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs, since the viruses used in the vaccine are grown in hens' eggs. For this reason, people who have an allergy to eggs should see an allergy specialist before receiving the influenza vaccine. Also, the vaccine is not recommended while individuals have active infections or active diseases of the nervous system. Less than one-third of those who receive the vaccine have some soreness at the vaccination site, and about 5% to 10% experience mild side effects, such as headache, low-grade fever, or muscle cramps, for about a day after vaccination. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past.
Another type of influenza vaccine (nasal spray) is made with live, attenuated (altered) influenza viruses. This vaccine is made with live viruses that can stimulate the immune response enough to confer immunity but do not cause classic influenza symptoms (in most instances). The nasal spray vaccine (FluMist) is only approved for healthy individuals ages 2 to 49. This nasal spray vaccine contains live, attenuated virus (less able to cause flu symptoms due to a designed inability to replicate at normal body temperatures). This live vaccine could possibly cause the disease in infants and immunocompromised people and does not produce a strong immune response in many older people. Side effects of the nasal mist include nasal congestion, sore throat, and fever. Headaches, muscle aches, irritability, and malaise have also been noted. In most instances, if side effects occur, they only last a day or two. This nasal spray has been produced for conventional flu viruses and should not be given to pregnant individuals or anyone who has a medical condition that may compromise the immune system, because in some instances the flu is the side effect. Caregivers should read the vaccine precaution insert before giving any vaccine, injectable or nasal, as these inserts are occasionally updated.