THURSDAY, Feb. 3 (HealthDay News) -- A single dose of the H1N1 swine flu vaccine was 93 percent effective during the 2009 pandemic, a new study found.

In order to assess the effectiveness of the vaccine -- known as the AS03-adjuvanted pandemic H1N1 vaccine -- Canadian researchers looked at 552 patients with flu-like illness who visited clinics in four provinces between Nov. 8 and Dec. 5, 2009.

Pandemic H1N1 was detected in 209 (38 percent) of the patients. Two (1 percent) of the patients with H1N1 flu had received a single dose of the H1N1 vaccine at least two weeks before they became ill, compared with 58 (17 percent) of patients who didn't have H1N1 infection.

The findings show that the vaccine was 93 percent effective, said the researchers, who were led by Danuta Skowronski at the British Columbia Centre for Disease Control in Vancouver.

The findings apply not only to Canada but other countries where vaccines were used, and may help guide the further development of influenza vaccine options, the researchers said.

More than 80 percent of the people in the study were younger than 50, so evidence of the effectiveness of the vaccine in the elderly is still needed, they noted.

The study appeared in the Feb. 3 online edition of BMJ.

More information

The U.S. Centers for Disease Control and Prevention has more about H1N1 flu.