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U.S.
Food and Drug Administration |
This article originally appeared in the November 1994 FDA Consumer. |
Though flu is expected to make its usual rounds this winter, many Americans won't have to suffer its high fever, characteristic cough, and possibly serious complications. A safe, effective vaccine is available.
It was not always so.
In 1918-1919--during the worst flu epidemic of all time--doctors had meager resources to fight the disease. To relieve symptoms, they relied on aspirin and other simple remedies. An influenza vaccine and antibiotics to combat pneumonia and other flu complications were years away from development. It has been estimated that over 20 million people died and possibly half the world's population came down with the flu in this global epidemic, or pandemic.
Influenza epidemics spread quickly through large populations because flu viruses are highly contagious. During flu's acute phase, respiratory tract secretions are rich in infectious virus and the disease is transmitted easily by sneezing and coughing. The incubation period lasts one to three days. Then symptoms--such as chills and fever that develop within 24 hours, headache often accompanied by sensitivity to light, sore muscles, backache, weakness, and fatigue--appear suddenly. Respiratory tract symptoms may be mild at first with a dry, unproductive cough, scratchy sore throat, and runny nose. As the person's temperature rises--sometimes to as high as 104 degrees Fahrenheit-- the muscle aches and headache get worse, and secondary bacterial infections, such as bronchitis and pneumonia, may move in. Ear infections are a common complication in children.
With no complications, acute symptoms usually subside after two or three days and the fever ends, although it may last as long as five days. Weakness and fatigue may persist for several weeks.
Today, we have several ways to defend people from influenza. The most important tool is immunization by a killed virus vaccine. Flu vaccines are licensed by FDA, and the exact composition of the vaccine varies each year, depending on the flu strains scientists expect to be most common. (See "This Year's Vaccine.") Influenza viruses have the ability to change themselves, or mutate, thereby becoming different viruses. Having the flu once does not confer lasting immunity, as is the case with some childhood viral diseases. The antibodies people produce in response to the one flu virus don't recognize and, therefore, donœt provide immunity to a different flu virus. Because the immunity conferred by a flu shot lasts for only about a year--and because different flu strains may circulate each season--individuals who want to be protected from flu should be vaccinated annually.
It takes two to four weeks for antibodies to develop after the vaccine is given. Therefore, the ideal time to get the flu vaccine is mid-October to mid-November, before the start of the flu season, which lasts from about December to March in the Northern Hemisphere. (Travelers should be aware that flu season lasts all year in some tropical climates, and in the Southern Hemisphere occurs from April to September.)
Vaccination is available to anyone who wants it and whose doctor agrees it would be beneficial. The Public Health Service's Advisory Committee on Immunization Practices (ACIP) strongly recommends vaccination for:
To reduce the risk of transmitting flu to high-risk persons, such as the elderly, transplant patients, and people with AIDS (who may have low antibody response to the flu vaccine)--and also to protect themselves from infection-- ACIP recommends vaccination for doctors, nurses, hospital employees, employees of nursing homes and chronic-care facilities, visiting nurses, and home-care providers. Students, police, firefighters, and other essential workers and community service providers may also find vaccination useful.
In most cases, children at high risk for influenza complications may receive the flu vaccine when they receive other routine vaccinations, including DTP (diphtheria, tetanus and pertussis) and pneumococcal vaccines. Pregnant women who have a high-risk condition should be immunized regardless of the stage of pregnancy; healthy pregnant women may also want to consult their health-care providers about being vaccinated.
The flu vaccine cannot cause flu because it contains only inactivated viruses. Any respiratory disease that appears immediately after vaccination is coincidental. However, the vaccine may have some side effects, especially in children who have not been exposed to the flu virus in the past.
The most commonly reported side effect in children and adults is soreness at the vaccination site that lasts up to two days. Fever, malaise, sore muscles, and other symptoms may begin 6 to 12 hours after vaccination and may last as long as two days.
People should be aware that they may test HIV-positive with the ELISA test after a recent flu shot, says the national Centers for Disease Control and Prevention. CDC recommends retesting with the more accurate Western Blot test to rule out false positives.
The vaccine is not for everyone. People allergic to eggs--the vaccine is made from highly purified, egg-grown viruses that have been made noninfectious--or other vaccine components should consult a doctor before getting a flu shot because they may develop hives, allergic asthma, difficulty breathing, and other allergic symptoms. The vaccine should not be given to any person ill with a high fever until the fever and other symptoms have abated.
For these individuals, and persons expected to develop low levels of antibodies in response to the influenza vaccine because they have impaired immune systems, influenza-specific anti-viral drugs can be used for prevention during the flu season or after infection to relieve influenza symptoms.
The anti-viral agents Symmetrel (amantadine), approved by FDA in 1976, and Flumadine (rimantadine), a chemically similar drug approved by FDA in September 1993, are safe and effective in preventing signs and symptoms of infection caused by various strains of the influenza A virus in children over 1, healthy adults, and elderly patients. These drugs may also be used for family members or close contacts of influenza A patients and for elderly nursing home patients who have been vaccinated but may need added protection. When a vaccine is expected to be ineffective because an epidemic is caused by strains other than those covered by the vaccine, anti-viral drugs may be used to provide protection against infection.
Either drug may be used following vaccination during a flu epidemic to provide protection during the two- to four-week period before antibodies develop. If an adult has already come down with the flu, treatment with Symmetrel or Flumadine has been shown to reduce symptoms and shorten the illness if administered within 48 hours after symptoms appear. Children with the flu can be treated with Symmetrel
About 5 to 10 percent of people who take Symmetrel experience nausea, dizziness and insomnia. There have been reports of more serious neurological adverse events, including seizures and aggravations of psychiatric illnesses. Flumadine has similar side effects, but at a lower rate.
Though many flu victims use over-the-counter preparations, such as decongestants and fever reducers, to make them feel more comfortable, none of these products affects the course of the disease.
Every year, about 20 percent of the U.S. population may become infected with flu, although each flu season is different. About 1 percent of those infected will require hospitalization because of complications, mostly bacterial pneumonia. Among those hospitalized, as many as 8 percent may die-- about 20,000 people in an average year. But the 1957-1958 "Asian flu" caused 70,000 deaths, and the 1968-1969 "Hong Kong flu" carried off 34,000 persons. The toll is usually greatest among the elderly.
The economic costs run high, too. From 15 million to 111 million workdays are lost each year, depending on the severity of the epidemic. Added to that are the costs of over-the-counter and prescription medicines, physician visits, hospitalization, and lost productivity.
It's no contest between the cost of a flu shot and the physical and other costs exacted by a bad case of the flu. A yearly vaccination early in the flu season is the best way to avoid this miserable disease.
FDA's Vaccines and Related Biologicals Advisory Committee meets in late January each year to decide which strains of influenza virus should be incorporated into the vaccine for the coming flu season, based on reports from national and international surveillance systems. A World Health Organization panel meets in Geneva in mid-February to make final recommendations for the next season's flu vaccine.
The vaccine choices for the United States take into consideration the predominant strain(s) circulating among the population in the current season (November, December, January) and any "new" strains that may have appeared both here and in other parts of the world. Another important part of the decision process is the examination of antibody levels in people vaccinated with the current year's vaccine to determine if they had a good immune response. Equally important is examining antibody levels in the same people to see if the vaccine offered any protection against recently identified "new" strains.
"You have to make this decision [about which strains to include in the vaccine] a year in advance before the flu season starts," says Helen Regnery, Ph.D., chief, strain surveillance section, influenza branch, national Centers for Disease Control and Prevention. "There is an inherent problem; FDA's advisory committee must decide for a future event, based on past and current knowledge of circulating strains, as well as the appearance of new strains of influenza."
Flu viruses are divided into three types--A, B and C--though the C type is not common. Influenza A viruses cause the most severe and widespread outbreaks, while influenza B causes limited, milder illness.
Influenza A viruses are classified into subtypes on the basis of two surface antigens (substances that induce antibody formation) called hemagglutinin (H) and neuraminidase (N). Currently, the circulating subtypes of influenza A that have been identified as causing extensive human illness are influenza A (H3N2) and influenza A (H1N1). Influenza A (H3N2) viruses have been much more prevalent than influenza A (H1N1) during the last five years.
"Last year's flu season [1993-1994] was more severe than average," says Nancy Arden, chief, influenza epidemiology, CDC. "More than 99 percent of the influenza viruses isolated and characterized were type A(H3N2) and most were similar to the A/Beijing/32/92 strain. Although people of all ages are susceptible to type A(H3N2), compared with influenza type A (H1N1) and type B, the A(H3N2) viruses are associated with more illness, complications and deaths among the elderly."
The 1993-1994 influenza season began in November 1993 and peaked in late December 1993 and early January 1994. By early March, influenza activity was undetectable or had declined to very low levels in most of the United States. As in other seasons when the A(H3N2) strains have predominated, the proportion of influenza-associated deaths was higher than average. Although it is still too early to estimate the actual number of such deaths during the 1993-1994 season, normally about 90 percent of these deaths occur among people 65 and older.
The trivalent influenza vaccine prepared for the 1994-1995 flu season will include A/Texas/36/91 (H1N1), A/Shangdong/9/93 (H3N2), and B/Panama/45/90, differing from the 1993-1994 vaccine only in the H3N2 component, which was A/Beijing/32/92 last season. The geographic name represents the place where the strain was isolated.
Evelyn Zamula is a free-lance writer in Potomac, Md.
Publication No. 95-1219
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