Medical Health Encyclopedia

Until recently the vaccine has been administered only with injection. A vaccine (FluMist) that can be delivered in a nasal spray has now been approved for people between 5 and 49 years of age. The vaccine contains live viruses that have been engineered to replicate in the cool temperatures of the nasal passages, but not in the warmer lungs and lower airways. Its presence in the nasal passages boosts the specific immune factors in the mucous membranes that fight off the epidemic viruses. Studies in 2003 reported protection against the flu that ranged between 66% and 92%, depending on whether the flu was A or B. (The lower rates were those observed for influenza B, particularly a new variant.) In a broad 2004 Canadian study, one to two doses of the intranasal spray offered significantly more effective protection to children (aged 15 - 71 months) than injected vaccines.  However, most insurance plans do not cover the cost of the intranasal vaccine. A preservative-free intramuscular injectable vaccine (Fluzone) is also now available.

Timing and Effectiveness of the Vaccine

Ideally, appropriate candidates should be vaccinated every October or November. However, it may take longer for a full supply of the vaccine to reach certain locations. In such cases, the high-risk groups should be served first.

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Antibodies to the flu virus usually develop within two weeks of vaccination, and immunity peaks within four to six weeks, then gradually wanes.

• Because children under age nine do not develop strong immune responses to one dose, the CDC recommends two vaccinations given one month apart.
• Early research also suggests that it may be equally effective to administer children’s vaccinations in the spring and fall, rather than one month apart; further study is ongoing.
• It should be noted that if an individual develops flu symptoms and is accurately diagnosed in time, vaccination of the other members of the household within 36 – 48 hours affords effective protection to those individuals, according to a 2004 Canadian analysis of multiple studies.