Two Shots for Kids, One for Preggers: U.S. Clarifies Swine Flu Vaccine Doses, Addresses Vaccine Safety Fears

Jon is a staff writer for Science.

U.S. policymakers erred on the side of caution in September when they recommended that children under 10 need two doses of the swine flu vaccine to develop a strong enough immune response to protect them from the disease. Now there’s strong evidence that they made the right call. New data also show for the first time that pregnant women need only a single shot.

At a press conference today, Anthony Fauci, head of the U.S. National Institute of Allergy and Infectious Diseases (NIAID), revealed the new data about these two groups, which are at high risk of developing severe disease from the novel H1N1 virus. As he explained, the trials tested the inactivated vaccine made in 389 children under 10 and in 50 pregnant women.

NIAID on 21 September reported preliminary data from the children’s study, which analyzed immune responses 8 to 10 days after participants received the vaccine and suggested the younger age brackets would need two doses. The new data confirm the preliminary findings.

Only 55% of those between the ages of 3 and 9 years of age had a “robust” immune response to the vaccine 21 days after a single dose. That dropped to 25% in children 6 months to 35 months of age. “However, there was a sharp increase in the immune response to the vaccine after they received a second dose,” said Fauci. Specifically, 8 to 10 days after receiving a second dose, 100% of the youngest children had a robust response, and 94% of the older group met that criteria. The vaccine did not cause any serious side effects.

The data conflict with recommendations from released last week from the World Health Organization, which said that it’s Strategic Advisory Group of Experts on Immunization reviewed data and concluded that children could get by with a single dose during these times of limited vaccine supply. “We’re trying very hard to base our decision on the scientific data,” said Fauci. “We would like to get children as fully protected as we possibly can.”

Clinical trials in 50 pregnant women in their second and third trimesters administered 15 micrograms to half the group and 30 micrograms to the other. The lower dose triggered what was deemed a protective antibody response in 23 of 25 women. Only one more woman reached that threshold in the group given the higher dose, so NIAID concluded that the lower dose is sufficient. Again, no serious side effects surfaced.

Fauci explained to ScienceInsider that the trial excluded women in the first trimester of pregnancy because that population has the highest miscarriage rate, and investigating the cause of each loss potentially could put the study on hold repeated. “The trial would never finish,” said Fauci. He stressed that no data have linked the vaccine to miscarriage.

As a reflection of the intense concern that many people have about taking the H1N1 vaccine or giving it to their children, the National Vaccine Program Office, a division of the Department of Health and Human Services, released a report today about its plans to monitor the pandemic vaccine’s safety. Bruce Gellin, vaccine office director, also said at the press conference that his office has convened an independent, special working group of the National Vaccine Advisory Committee to evaluate the safety data. Gellin said the group is having its first face-to-face meeting today, and plans to review the data biweekly. Each month, the committee will issue a report to the National Vaccine Advisory Committee, which holds meetings that are open to the public.

The U.S. Centers for Disease Control and Prevention today says that manufacturers have supplied the government with a total of 30 million doses of the H1N1 vaccine, but as of 28 October, only 16.8 million of those had been ordered by states and shipped to them.

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