Influenza (cont.)

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Are there any flu shot or nasal spray vaccine side effects in adults or in children?

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 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 not receive 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%-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. The intradermal shots reportedly have similar side effects as the IM shot but are less intense and may not last as long as the IM shot.

Nevertheless, some older people remember earlier influenza vaccines that did, in fact, produce more unpleasant side effects. Vaccines produced from the 1940s to the mid-1960s were not as highly purified as modern influenza vaccines, and it was these impurities that caused most of the side effects. Since the side effects associated with these early vaccines, such as fever, headache, muscle aches, and fatigue, were similar to some of the symptoms of influenza, people believed that the vaccine had caused them to get the flu. However, injectable influenza vaccine produced in the United States has never been capable of causing influenza because it consists of killed virus.

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 2-49 years of age. 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 spray vaccine 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 may be a side effect. Caregivers should read the vaccine precaution insert before giving any vaccine, injectable or nasal, as these inserts are occasionally updated.

Some people do not receive influenza vaccine because they believe it is not very effective. There are several different reasons for this belief. People who have received influenza vaccine may subsequently have an illness that is mistaken for influenza, and they believe that the vaccine failed to protect them. In other cases, people who have received the vaccine may indeed have an influenza infection. Overall 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. Because the vaccine strains must be chosen nine to 10 months before the influenza season, and because influenza viruses mutate over time, sometimes mutations occur in the circulating virus strains between the time the vaccine strains are chosen and the next influenza season ends. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine efficacy. This commonly occurs with the conventional flu vaccines as the specific virus types chosen for vaccine inclusion are based on reasoned projections for the upcoming flu season. Occasionally, the vaccine does not match the actual predominating virus strain and is not very effective in generating a specific immune response to the predominant infecting flu strain. For the 2011-2012 flu season, the seasonal trivalent vaccine contains a H1N1 strain (swine flu strain) of virus that was one of the predominating pandemic viral strains in 2009-2010. Fortunately, it also contains the H3N2 virus that predominated in a few regions in 2010-2011. However, it does not protect well against the newest type H3N2v strain that has appeared in 2012.

Vaccine efficacy also varies from one person to another. Studies of healthy young adults have shown influenza vaccine to be 70%-90% effective in preventing illness. In the elderly and those with certain chronic medical conditions such as HIV, the vaccine is often less effective in preventing illness. Studies show the vaccine reduces hospitalization by about 70% and death by about 85% among the elderly who are not in nursing homes. Among nursing-home residents, vaccine can reduce the risk of hospitalization by about 50%, the risk of pneumonia by about 60%, and the risk of death by 75%-80%. If antigenic drift results in changing the circulating virus from the strains used in the vaccine, vaccine efficacy may be reduced. However, the vaccine is still likely to lessen the severity of the illness and to prevent complications and death.

Medically Reviewed by a Doctor on 2/20/2013

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