How well will the vaccine protect against the H1N1 flu virus?

Most people will develop immunity in about 10 days after the H1N1 flu shot. Clinical trials have shown 85% to 98% of healthy adults developed an immune response strong enough to offer protection against the virus.

The vaccine may not work as well in people who have problems with their immune systems or who are taking medication that affects their immune systems, however it is still very important for these people to be vaccinated.