"The take-home point is that people should get the flu shot," said Neil Fishman, director of infection prevention at the Hospital of the University of Pennsylvania.
Unlike in some previous years, the flu vaccine appears effective and supplies are plentiful. The body takes about two weeks to develop immunity against a disease that can be deadly, especially in the elderly.
Influenza comes in many forms, and they differ in susceptibility to various medications, when and where they circulate, severity of illness, and other factors.
Epidemiologists said the influenza type A strain known as H1N1 is often the first to show up, as it was this year.
The U.S. Centers for Disease Control and Prevention reported on Friday that 86 of the 88 of the H1N1 samples tested were resistant to Tamiflu, known generically as oseltamivir. The Pennsylvania Department of Health confirmed resistance in one sample each from Erie and Bucks Counties.
None of the other type A or B flu strains reported this year has shown a similar resistance, but physicians can't tell what strain a patient has - and what drug would work - without a laboratory test, which often is unavailable. The antivirals must be given within 48 hours of first symptoms to be effective.
"It is very tricky," said Esther Chernak, medical director of Philadelphia's acute communicable disease control program. "It will make the control of influenza in high-risk settings like hospitals and nursing homes more complicated."
Though most people take a drug such as Tamiflu to feel better faster - its main benefit has been to reduce the misery by just one or two days - the drug can serve more urgent needs in those with compromised immune systems, even if they have been vaccinated.
"Elderly people don't always produce robust antibodies," said William Kavesh, director of the geriatric clinic at the Philadelphia VA Medical Center.
