In addition to periodic global pandemics, during which hundreds of thousands or even millions may die, flu claims thousands of American lives every winter. With the introduction of the first flu vaccines in the 1940s, infectious disease experts took a big step toward limiting the impact of influenza. For nearly 60 years, flu vaccines were administered via injection. In June 2003, the U.S. Food and Drug Administration licensed FluMist, the first nasally administered flu vaccine, for use in healthy people aged 5 to 49 years.
Dead or Alive
When your doctor gives you a vaccination, it triggers an immune response that leads to production of protective antibodies. These antibodies then protect you from being infected by whatever agent was contained in the vaccine. Some vaccines contain inactivated, or killed, pathogens, while others contain living but weakened pathogens. Living pathogens, even when weakened, may cause more undesirable side effects than killed organisms. Injectable flu vaccines contain killed viruses, while FluMist contains live, weakened viruses.
Problems for the Very Young
Two years after FluMist was introduced, the FDA extended its licensing to include healthy children down to 2 years of age. FluMist is not approved for use in children under 2 because studies showed an unacceptably high rate of wheezing and hospitalization in younger children who received this vaccine. FluMist is still not recommended for children up to age 5 who have had recurrent wheezing, nor is it recommended for anyone with asthma, regardless of age. The respiratory symptoms associated with FluMist stem from its live-virus formulation and its route of administration. Introducing live viruses, even though they are weakened, into your nasal passages may trigger wheezing, sore throat, fever and other side effects.
Issues for Older People
As people age, their immune systems gradually weaken. This phenomenon is called “immunosenescence.” According to a 2010 review in "Mayo Clinic Proceedings," elderly individuals -- unlike children or young adults -- may not develop adequate immunity if they receive an intranasal influenza vaccine. It is not yet clear if immunosenescence plays a role in this poor response or if many years of exposure to similar flu viruses somehow interferes with FluMist's effectiveness. Until this issue is clarified, choose an injectable flu vaccine if you are age 50 or older. Your doctor may even recommend a higher-potency flu shot to account for immunosenescence.
While FluMist appears to be safe for healthy persons from age 2 to 49 years, in some situations, a traditional flu shot may be better, even if you think you can take FluMist. Because FluMist contains live viruses, only people with healthy immune systems should receive this vaccine. People whose immune systems are impaired due to HIV infection, long-term corticosteroid use or other factors should get flu shots, rather than FluMist, due to a higher risk for side effects with a live-virus vaccine. For the same reason, people with certain medical conditions, such as chronic lung disease, heart failure or diabetes, should receive flu shots. FluMist is not licensed for use in pregnant women. Your doctor can help you decide which flu vaccine is best for you.
- Philosophical Transactions of the Royal Society of London: Towards Universal Influenza Vaccines?
- U.S. Food and Drug Administration: June 17, 2003 Approval Letter: Influenza Virus Vaccine Live, Intranasal
- U.S. Food and Drug Administration: FDA Approves Nasal Influenza Vaccine for Use in Younger Children
- Mayo Clinic Proceedings: Influenza Vaccines: From Surveillance through Production to Protection
- Comstock Images/Comstock/Getty Images