How Effective is the H1N1 (Swine Flu) Vaccine?

By Julie Stachowiak, PhD
Multiple Sclerosis Guide; Guest blogger

The simple answer is "it depends who is vaccinated."

Here is the good news and what we DO know. The H1N1 vaccine has an advantage over the seasonal flu vaccine (which has an efficacy of 70 to 90%), because those vaccines are based on educated guesses as to which strains of flu will be circulating a hemisphere away after a good 8 to 10 months has elapsed. Usually the guesses are pretty good, but there can be some "misses."

With H1N1, the vaccine is made of the exact virus that we know is circulating.

Here is something else we do know - one dose of the H1N1 shot has shown to produce adequate immunity in 92 percent of the pregnant women who were immunized.

However, it looks like children probably will still need two doses, as only about one-third of kids under 10 years old developed adequate antibody levels 10 days following the vaccine. It is possible that they could continue to build immunity, and further reports are going to be coming soon (although adults' antibody levels at 10 days post-vaccine and 21 days post-vaccine were about the same).

Also, it is possible that people who are immunocompromised, such as people with HIV, may require two doses to confer immunity. Trials are still ongoing to determine this.

Bottom line: The H1N1 vaccine works. Depending on who is getting vaccinated, two doses may be required.