One dose of H1N1 vaccine may be enough for infants and children, but caution urged

Kathleen Blanchard's picture

New findings show that one dose of H1N1 flu vaccine may provide adequate immunity for infants and children, who have been widely affected by pandemic H1N1 inluenza. The current recommendation for H1N1 flu vaccine in children is two doses, 21 days apart. Until findings are definitive, caution is urged that one dose of H1N1 vaccine may not provide protection to children in all countries, and may vary between vaccine manufacturers.

Researchers studied antibody levels in children younger than nine years of age, finding that one dose of H1N1 vaccine seems to be enough to protect children from H1N1 flu and prevent spread of the disease.

This study is published by ahead of print due to the public health implications. Australian researchers randomized two groups of children between age six months and nine. The children received two doses of H1N1 vaccine, 21 days apart, and either a dosage of 15 µg or 30 µg.

Comparing the two doses, and looking at antibody titers following the first and second doses of H1N1 flu vaccine, the researchers concluded that one dose of H1N1 vaccine, 15 µg, will provide sufficient protection from H1N1 flu and would be well tolerated.


For this study 370 children were examined. "Following the first dose of vaccine, antibody titers of 1:40 or greater were observed in 161 of 174 infants and children in the 15-microgram group (92.5 percent) and in 168 of 172 infants and children in the 30 microgram group (97.7 percent)," the authors report. All participants demonstrated antibody titers of 1:40 or greater after the second vaccine dose," [high enough to protect against the H1N1 virus]. The researchers note that the majority of adverse reactions to the vaccine were mild to moderate in severity. The immune responses to the vaccine were strong regardless of age, baseline antibody status, or whether the child had received a seasonal influenza vaccination prior to this study."

The authors say one dose of 15 µg of H1N1 flu vaccine may be effective and well tolerated", providing enough protection against H1N1 flu. The authors noted that H1N1 flu vaccine protects infants and children, and that one dose of the vaccine may be enough to raise antibody titers and prevent spread of the disease.

The editorial authors of the study say caution should be used, however. A single dose of H1N1 flu vaccine may not protect all children. "The immunogenicity data presented by Nolan et al suggest that at least some children will be protected after a single 15-microgram dose of the H1N1 vaccine used in this study, but the findings cannot be generalized with confidence to all children, epidemiological circumstances in every country, or different vaccine formulations."

Until more data rolls in as to whether H1N1 vaccine protects children after just one dose, the editorialists say it would be "prudent" to keep giving children two doses of H1N1 flu vaccine.

JAMA. 2010: 303[1]:[doi: 10.1001/JAMA.2009.1929