A preliminary study released in the New England Journal of Medicine September 10, 2009 shows that 1 dose of 15 mcg induced an immune response in 96.7% of volunteers tested in Australia.

The trial tested the efficacy of 15 mcg vs 30 mcg dose of the new H1N1 (Swine) flu vaccine. A total of 240 people were divided into 2 groups, those under 50 years of age and those over 50, and were randomized to receive 2 doses of either 15 mcg or 30 mcg.

Antibody titres were checked after 21 days. A robust immune response was shown after receiving 1 dose of the 15 mcg dose (96.7%) versus the 30 mcg dose (93.3%) Given these results, further investigation of the lower dose will be explored.

Given that the study was conducted in healthy individuals, the authors concluded that more research needs to be done on other populations such as the elderly, children and those with compromised immune systems to see if the same robust response is achieved with one dose of the lower antigen.

This study however is great news for the manufacturers of the vaccine because it raises the possibility that there will now be enough supplies, if one dose is needed, to vaccinate the 160 million Americans in the high priority groups (pregnant women, children 6 months – 24 years, and adults 25-65 with chronic disease, health care workers and adults who take care of infants <6months). This accounts for about 1/2 of all Americans.