Pneumonia - Prevention

Viral Influenza Vaccines (Flu Shot)

Description of Vaccines. Vaccines againstthe flu (or a "flu shot") useinactivated (not live) viruses. They are designed to provoke the immune system to attack antigens contained on the surface of the virus. Antigens are foreign molecules that the immune system specificallyrecognizes andtargets for attack.

Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy them.

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Unfortunately, the antigens in these influenza viruses undergo genetic alterations (called antigenic drift) over time, so they are likely to become resistant to a vaccine that worked in the previous year. Vaccines are then redesigned annually to match the current strain.

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 changes.
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) for healthy people aged 5 to 49 years is approved by the FDA. It is known as a live, attenuated, trivalent, 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 isa nasal spray. In one study it protected up to 93% of children against the flu.

Timing and Effectiveness of the Vaccine. Ideally, people should get a flu shotevery 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 two weeks of vaccination.Immunity peaks within four to six weeks, then gradually wears off. That is why most people should get a flu shot every year.