BETHESDA, Md -- November 09, 2009 -- Healthy pregnant women mount a robust immune response following just 1 dose of the influenza A(H1N1) vaccine, according to initial results from an ongoing clinical trial by the National Institutes of Health.
"For pregnant women, who are among the most vulnerable to serious health problems from 2009 H1N1 infection, these initial results are very reassuring," said Anthony S. Fauci, MD, National Institute of Allergy and Infectious Diseases (NIAID), Bethesda, Maryland.
"The immune responses seen in these healthy pregnant women are comparable to those seen in healthy adults at the same time point after a single vaccination, and the vaccine has been well tolerated."
According to the Centers for Disease Control and Prevention (CDC), since the outbreak began last spring, at least 100 pregnant women have been hospitalised in intensive care units in the United States and at the last official count, 28 pregnant women have died.
A preliminary analysis of blood samples taken 21 days post-vaccination from a subgroup of 50 pregnant women participating in the trial showed that 25 women who received a single 15-mcg dose of the vaccine, the H1N1 vaccine elicited an immune response likely to be protective in 92% (23/25) of these women.
In 25 women who received a single 30-mcg dose of the vaccine, the H1N1 vaccine elicited an immune response likely to be protective in 96% (24/25) of these women.
The trial began on September 9 and reached its target enrollment of 120 volunteers in mid-October. All participants are aged 18 to 39 years and began the study in their second or third trimester (14 to 34 weeks) of pregnancy.
At entry into the study, the participants were divided at random into 2 groups: half are receiving 2 doses of a 15-mcg vaccine and the other half are receiving 2 doses of a 30-mcg vaccine. The two injections of vaccine are spaced 3 weeks apart.
Safety is being monitored closely in the trial, by the study investigators and by a safety monitoring committee. To date, the vaccine appears to be well-tolerated, and no safety concerns related to the vaccine have arisen.
Like the seasonal flu vaccine, the 2009 H1N1 vaccine contains a purified portion of the killed virus and therefore cannot cause infection. The vaccine does not contain the preservative thimerosal or an adjuvant.
SOURCE: National Institutes of Health
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