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Immunizations

Description

An in-depth report on the purpose of immunizations and recommended schedules.


Alternative Names

Measles; Rubella; Tetanus; Vaccinations; Whooping cough


Viral Influenza

Influenza, commonly called the flu, is always caused by a virus.

Influenza
Influenza, also known as the flu, is caused by a virus.

There are different strains of influenza:

Based on a final analysis of the 2001-2002 flu season, nearly 90% were type A and about 10% were type B. Influenza A usually causes more severe disease than type B. However, because influenza B has been less common in the past few years, there is some concern that some people -- particularly small children -- may have fewer antibodies to it and so may be at higher risk for severe infection. (See Flu Vaccines in this report.)

Complications of the Flu. In general, the flu is usually self-limited and not serious. It is responsible, however, for 15 - 30% of the excess number of hospitalizations that occur in winter. About 1% of people who contract the flu end up in the hospital, and an estimated 36,000 people currently die each year of flu-related complications. The highest risks for serious complications occur in people age 65 and older and in those who are already sick with another disease. There have also been reports of flu-related deaths in very young children.

Pneumonia is the major serious complication of the flu and can be very serious. It can develop about five days after viral influenza. It is an uncommon event, however. It nearly always occurs in high-risk individuals, such as the very young or very old, and hospitalized or immunocompromised patients.

Note on Pandemics. Every year, flu strikes millions of people worldwide. Influenza epidemics are most serious when they involve a new strain against which most people are not immune. Such so-called pandemics can infect more than one fourth of the world's population within a three-month period. For example, the Spanish flu in 1918 and 1919 killed 20 million people in the US and Europe and 17 million in India. Although pandemics are still of great concern, there have been major improvements in private and public health since then, including the discovery of antibiotics to treat bacterial complications, new anti-viral agents and vaccines, and intensive world-wide surveillance of outbreaks.

Flu Vaccines

Description of Vaccines. Vaccines against the flu use inactivated (not live) viruses. The influenza vaccine is commonly called a "flu shot." It is designed to provoke the immune system to attack antigens contained on the surface of the virus. (Antigens are foreign molecules that the immune system specifically recognizes as alien and so targets for attack.)

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.

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.

Antibodies to the flu virus usually develop within 2 weeks of vaccination, and immunity peaks within 4 - 6 weeks, then gradually wanes.

In healthy adults, immunization typically reduces the chance of the flu by about 70 - 90%. The current flu vaccines may be slightly less effective in certain patients, such as the elderly and those with certain chronic diseases. Some evidence suggests, however, that even in people with a weaker response, the vaccine is usually protective against serious flu complications, particularly pneumonia. The major outstanding question is whether the vaccination prevents complications of serious illness. One 2003 study, for instance, reported no reduction in severity of chronic lung diseases among vaccinated patients with asthma, emphysema, or chronic bronchitis. Some evidence suggests, on the other hand, that among the elderly, a flu shot may help protect against stroke, adverse heart events, and death from all causes.

Candidates for the Flu Vaccine

Children Who Should Be Vaccinated. The following children over 6 months should be vaccinated against the flu:

Of note: There has been some question concerning flu shots because of some reports that vaccines may worsen asthma. Recent and major studies have been reporting, however, that the vaccination is safe for children with asthma. It is also very important for these patients to reduce their risk for respiratory diseases. Still, 90% of asthma patients remain unvaccinated.

Older Children and Adults Who Should Be Vaccinated. The following in order of priority are the population groups who should be vaccinated each year. The first two groups have the highest need for flu shots and are given top priority:

Other adults who should consider flu shots include:

Side Effects

Possible side effects include:


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