- Influenza A. The influenza A virus is further categorized by primary molecular antigens (hemagglutinin and neuraminidase), which serve as the targets for the vaccines. Influenza A is a particular problem because it can infect other species, such as pigs or chickens, and undergo major genetic reassortments.
- Influenza B viruses tend to be more stable than influenza A viruses, but they too vary. Although influenza B has been far less common than A, a vaccine for type B is important because experts are concerned that small children will not have developed any immunity to the virus and will experience severe flu if they are exposed to type B.
A live but weakened intranasal vaccine (FluMist) is proving to be effective and safe in healthy people aged 5 - 49 years and has been approved by the FDA. It is known as a live, attenuated, intranasal influenza vaccine (LAIV). The vaccine is engineered to grow only in the cooler temperatures of the nasal passages, not in the warmer lungs and lower airways. It boosts the specific immune factors in the mucous membranes of the nose that fight off the actual viral infections. FluMist is employed using a nasal spray. In one study , FluMist provided protection against the flu in up to 93% of children. According to a broad Canadian study in 2004, one to two doses of the intranasal spray gave children better protection than injected vaccines.
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.
Antibodies to the influenza virus usually develop within 2 weeks of vaccination, and immunity peaks within 4 - 6 weeks, then gradually wanes.
- Because children under age 9 do not develop strong immune responses to one dose, the CDC recommends two vaccinations given 1 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 influenza 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.
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