Influenza

V

Treatment and Prevention

There is no specific cure for influenza. Recommended treatment usually consists of bed rest and increased intake of nonalcoholic fluids until fever and other symptoms lessen in severity. Certain drugs have been found effective in lessening flu symptoms, but medical efforts against the disease focus chiefly on prevention by means of vaccines that create immunity.

A

Drugs That Ease Symptoms

No drugs can cure influenza, but certain antiviral medicines can relieve flu symptoms. Available by prescription, these drugs provide modest relief, but only if taken on the first or second day of symptoms. The drugs amantadine (sold under the brand name Symmetrel) and rimantadine (Flumadine), both in pill form, work against hemagglutinin and are effective in treating type A influenza. Two other drugs inhibit neuraminidase and are effective against both type A and type B strains: oseltamivir (Tamiflu) is in pill form and zanamivir (Relenza) is an inhalant.

B

Vaccines

A flu vaccine consists of greatly weakened or killed flu viruses, or fragments of dead viruses. Antigens in the vaccine stimulate a person’s immune system to produce antibodies against the viruses. If the flu viruses invade a vaccinated person at a later time, the sensitized immune system recognizes the antigens and quickly responds to help destroy the viruses.

About 5 to 10 percent of people who receive a flu vaccine experience mild, temporary side effects, typically soreness at the injection site. Young children who have not previously been exposed to the influenza virus are most likely to have side effects.

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Flu viruses constantly change so different virus strains must be incorporated in vaccines from one year to the next. Scientists try to provide a good match between the vaccine and the most serious virus strains circulating at the time. But because it takes months to manufacture and distribute vaccines, decisions on their composition must be made well before the start of each flu season. Each February experts at the World Health Organization (WHO) recommend the composition of the vaccine for the forthcoming winter in the Northern Hemisphere; a second recommendation is made in September for vaccines to be used in the Southern Hemisphere. Typically vaccines contain antigens from three virus strains, usually two type A and one type B.

According to the CDC, the success of flu vaccines varies from one person to another. In healthy young adults, the vaccines are 70 to 90 percent effective in preventing the disease. In the elderly and people with certain chronic medical conditions, the vaccines are less effective in preventing illness but help reduce the severity of an infection and the risk of major complications or death. Studies show that flu vaccines reduce hospitalization by about 70 percent and death by about 85 percent among elderly people.

C

Recommendations for Flu Shots

The CDC recommends annual flu shots for people who are at high risk for developing serious complications as a result of an influenza infection. This group includes all people age 65 and older; people in nursing homes and other facilities that house people with chronic medical conditions; people with chronic heart, lung or kidney disease, diabetes, an impaired immune system, or severe forms of anemia; children and adolescents with conditions treated for long periods of time with aspirin (which makes them vulnerable to Reye’s syndrome); and women who will be in the second or third trimester of pregnancy during the influenza season.

To help stop the disease’s spread, the CDC also recommends vaccination for health-care workers, employees of nursing homes and chronic-care facilities, and household members of people in high-risk groups. Doctors encourage individuals who travel to areas of the world where influenza viruses circulate to receive the most current vaccine, particularly if they are at higher risk of complications.

It takes the human immune system one to two weeks after vaccination to develop antibodies to the flu antigens. According to the CDC, the best time to get flu shots in the United States is between October 1 and mid-November—sufficiently in advance of the peak of influenza activity, which in the United States generally lasts from late December until early March.

Flu shots must be given annually for two reasons. First, antibody protection provided by the vaccine decreases during the year following vaccination. Second, vaccines created for pre-existing viral strains may not work against new strains; nor does an infection with one flu strain confer immunity to infection by another strain.

VI

Historic Outbreaks and Pandemics

Evidence suggests that all influenza viruses in mammals, including humans, derived from viruses in wild ducks and other waterfowl. Some of these viruses could have been acquired by humans thousands of years ago. But medical historians know of no clearly identifiable influenza epidemics until large-scale outbreaks occurred in Europe in 1510, 1557, and 1580. The 1580 outbreak also spread into Africa and Asia, making it the first known pandemic. Pandemics have occurred periodically ever since. Major pandemics took place in 1729-1730, 1732-1733, 1781-1782, 1830-1831, 1833, and 1889-1890. The last of these, called the Russian flu because it reached Europe from the east, was the first pandemic for which detailed records are available.

In the 20th century, major pandemics occurred in 1918-1919, 1957-1958, and 1968-1969. The 1918-1919 pandemic was the most destructive in recorded history. It started as World War I (1914-1918) was ending and caused from 20 million to 50 million deaths—two to five times as many deaths as the war itself. When and where the pandemic began is uncertain, but because Spain experienced the first major outbreak, the disease came to be called the Spanish flu. The virus was exceptionally lethal; many of the deaths were among young adults age 20 to 40, a group usually not severely affected by influenza.

Scientists succeeded in reconstructing the 1918 influenza virus in 2005 after finding samples of the virus in the preserved tissues of three people killed by the Spanish flu. The scientists concluded that it was an avian flu virus that spread directly to humans. The virus penetrated deep into human lung tissue, causing a type of pneumonia that was capable of killing the young and healthy.

In 1957 a flu outbreak occurred in Guizhou, a province in southwestern China. Within six months, most areas of the world were battling what became known as Asian flu. Before the 1957-1958 pandemic subsided, an estimated 10 to 35 percent of the world’s population had been affected. The overall mortality rate, however, was comparatively low.

About a decade later, a variant of the virus that caused the 1957-1958 pandemic originated in either Guizhou or Yunnan province in southern China. The variant was first isolated and identified in Hong Kong in July 1968. Within a few months, cases of this Hong Kong flu appeared around the world. Hardest hit by the pandemic were children under age 5 and adults aged 45 to 64. In the United States, an estimated 30 million people were infected and there were some 33,000 influenza-related deaths.

No additional pandemics occurred during the 20th century or at the beginning of the 21st century, but public health experts expect that there will be more pandemics in coming years. While scientists do not yet know how to accurately predict flu outbreaks, they have established an international network to track and monitor outbreaks so that health officials can take immediate preventive measures to avoid pandemics. The international network, called FluNet, consists of about 110 influenza centers in more than 80 countries and several World Health Organization (WHO) centers, all linked electronically.

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