Strong Immune Response by Healthy Pregnant Women to H1N1 Vaccine

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An ongoing clinical trial finds that healthy pregnant women have a strong immune response after receiving just one dose of H1N1 influenza vaccine. The trial, which began on September 9, is sponsored by the National Institute of Allergy and Infectious Disease (NIAID) of the National Institutes of Health.

Both the Centers for Disease Control and Prevention (CDC) and its Advisory Committee on Immunization Practices (ACIP) recommend that pregnant women receive the inactivated influenza H1Na monovalent vaccine during any stage of pregnancy. This recommendation is based on the fact that pregnant women are at increased risk for severe disease and serious complications, including death, from influenza. Compared with the general population, a greater proportion of pregnant women infected with the H1N1 influenza virus have required hospitalization and have died.

Yet many pregnant women are concerned about receiving the vaccine because of fears about testing. The results of this ongoing trial may put those fears to rest. According to NIAID Director Anthony S. Fauci, MD, “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.”

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The H1N1 trial enrolled 120 healthy pregnant women, who were randomly assigned to receive either 15-microgram or 30-microgram doses of the H1N1 vaccine three weeks apart. All participants are ages 18 to 39 and entered the study during their second or third trimester of pregnancy. The vaccine does not contain the preservative thimerosal or an immune boosting substance.

Although the trial is ongoing, the results thus far show that in 25 women who received a single 15-microgram dose of the H1N1 influenza vaccine, the vaccine elicited an immune response likely to be protective in 23 (92%) of the women. Among 25 women who received a single 30-microgram dose, the vaccine elicited an immune response likely to be protective in 24 (96%) of the women.

Additional results of the trial will be reported. Thus far, the H1N1 vaccine appears to be well tolerated by healthy pregnant women, and the trial researchers have not encountered any safety issues related to the vaccine.

SOURCE: National Institutes of Health/NIAID

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