If the H1N1 virus is to continue its contagious ways this coming flu season, it will have to adapt to a highly immune population, according to a new study.
Epidemiologists estimate that 183 million Americans — 59 percent of the U.S. population — are already immune to the pandemic H1N1 strain of the influenza virus, also known as swine flu.
People have become immune because they’ve been either exposed to the virus or vaccinated, the researchers say. Immune people have built up antibodies to defend against the outside invader.
“Every person who is vaccinated is one fewer the virus can find,” said study researcher Dr. David Morens, senior adviser to the director of the National Institute of Allergy and Infectious Diseases.