Evidence is increasing that common influenza viruses are becoming resistant to the main drug used to treat them. The drug is oseltamivir, also known as Tamiflu.

The most common ___41___ flu virus found in the United States this year is type A (H1N1). During the last flu season, twelve percent of H1N1 viruses ___42___ in the United States were resistant to Tamiflu. This year, researchers at the Centers for Disease Control and Prevention say ___43___ is close to 100 percent. Still, they say early reports show that flu___44___ has been low so far this year.

The research team is reporting its findings in the Journal of the American Medical Association. Alicia Fry led the team. Doctor Fry says it is better to prevent the flu than to have to ___45___ it. And the best form of prevention, she says, is getting vaccinated (进行预防接种) each year against influenza.

Viruses change, or mutate, (变异) so flu vaccines must be reformulated each year to target the most common threats.

But last week, two teams working ___46___ reported a discovery that could help lead to a universal flu vaccine. The hope is to develop a vaccine that could give ___47___ protection against a majority of flu viruses, including bird flu.

The scientists ___48___ a protein that inactivates the flu virus before it can mutate.

One team used an antibody found in blood donated by an individual. Scientist Ian Wilson at the Scripps Research Institute in California says the antibodies proved ___49 ___ effective in laboratory mice exposed to deadly levels of virus. He says they gave complete protection .