Physicians discuss flu season, new flu medicines (1-13-00)
Batten down the hatches, Texas: flu season has hit the East Coast and is moving to the Lone Star State.
January and February are the heaviest months for influenza in San Antonio, say infectious disease specialists from The University of Texas Health Science Center at San Antonio. The flu season typically ends in March.
Type A influenza is accounting for nearly all of the cases of flu being reported this winter. "Type A usually is the predominant type, but Type B can cause a significant number of infections," said Charles Leach, M.D., associate professor of pediatrics at the Health Science Center. "In 1992-93, for example, 86 percent of the influenza cases were caused by Type B. Last year, 21 percent of the cases were attributed to it. This year, the Centers for Disease Control is reporting 99.8 percent are caused by Type A."
The predominant strain of influenza currently is the A/Sydney H3N2 strain, said Jean Smith, M.D., associate professor of medicine, who sees many older flu patients. The A/Sydney strain is one of the strains included in the current flu vaccine, which is usually administered to patients at least two weeks prior to any anticipated influenza activity.
Influenza, a respiratory illness that may be spread by sneezing and coughing, may occur even in vaccinated individuals. "The vaccine is not 100 percent protective even in a healthy population and is less effective in the frail elderly or immune-compromised patients," Dr. Smith said. "In addition, only about two-thirds of people over the age of 65 have actually received the vaccine in past years."
Jan Patterson, M.D., professor of medicine and pathology at the Health Science Center and medical director of infection control at University Hospital, said the flu vaccine is 70-90 percent effective in most adults but only 30-70 percent effective in elderly patients in nursing homes. The vaccine cuts down on post-influenza complications such as bacterial pneumonia, she said.
About 700 people died from pneumonia and influenza in San Antonio in 1999, according to the Morbidity and Mortality Weekly Report of the U.S. Centers for Disease Control and Prevention. Nearly 300 of those deaths occurred in January, February and March during last yearís flu season.
Substantial attention is being paid to two new anti-influenza drugs, Relenza and Tamiflu, which are comparable in their ability to make patients feel better quicker, said Drs. Leach and Smith. Taken in time after flu effects are felt, these drugs may shorten the duration of the illness. "Major symptoms resolve one to one-and-a-half days earlier," Dr. Leach said. "However, patients must start treatment in the first two days of illness."
Relenza is given by inhalation; Tamiflu is an oral pill. "My clinical opinion is that there is little evidence for the superiority of one drug over the other," Dr. Smith said.
The U.S. Food and Drug Administration approved the drugs for use in adults, but testing on pediatric application is not complete. Tamiflu currently is not FDA approved for individuals under 18 and Relenza is not approved for children under 12.
In senior citizens, the drugs generally are well tolerated but some patients with significant renal (kidney) dysfunction may need to take lower doses of Tamiflu.
Relenza and Tamiflu work by inhibiting neuraminidase, an enzyme on the surface of the influenza virus. Blocking this enzyme impairs the virusí ability to leave infected cells and to move along the respiratory tract to involve uninfected cells, Dr. Smith said.
The drugs are chemical compounds, unlike the annual flu vaccines, which are made from inactivated influenza viruses. "The vaccine is still the mainstay of prevention for the population at large," Dr. Smith said.
Older drugs were effective only against Type A influenza, but Relenza and Tamiflu are effective against Types A and B. "That may not be of major importance this year, since so few of the infections are Type B-related, but it could be critical in future years," Dr. Leach said.
When will flu season end? It varies from year to year, just like the start of flu season. "Last year the flu season in San Antonio was later than usual, not starting until February," Dr. Smith said. "December or January is more usual. Usually the season is over by the end of March."
Dr. Patterson said that from what she has heard, "this is a bad year for the flu."
Tips for avoiding the flu
[Source: Jan Patterson, M.D., The University of Texas Health Science Center at San Antonio]
Contact: Will Sansom