TORONTO — Infants 6–12 weeks of age can safely and effectively be vaccinated against influenza, Dr. Janet Englund reported in a late-breaking abstract presentation at the annual meeting of the Infectious Diseases Society of America.
In a randomized, double-blind, placebo-controlled trial conducted in nearly 1,400 healthy U.S. infants aged 6–12 weeks, those babies who received the Fluzone trivalent inactivated influenza vaccine (TIV) demonstrated statistically significant increases in antibody responses for all three influenza strains (A [H1N1], A [H3N2], and B) in the vaccine compared with infants who were given placebo. Additionally, “no significant differences were seen between the two groups in any safety outcomes,” said Dr. Englund, of Seattle Children's Hospital, who reported the findings on behalf of the clinical study (GRC28) team.
“Currently, TIV is licensed and recommended for all children [aged 6–59 months]. The standard of care for infants younger than 6 months is to do nothing, even though this group has the highest risk for hospitalization for influenza-related illnesses,” Dr. Englund said. “The goal of this study was to determine whether delivering TIV at the same time as routine vaccinations in these young infants would enhance their protection.”
Of 1,376 infants aged 6–12 weeks enrolled in the investigation, 916 were randomized to receive two doses of TIV 1 month apart along with indicated concomitant immunizations, and 460 were randomized to receive placebo. The mean age at first influenza vaccination was 9.1 weeks. The primary outcome measure was antibody response to the three vaccine antigens in the 2005–2006 trivalent inactivated influenza vaccine after two doses, as determined by hemagglutination-inhibition antibody titers.
Of the initial study participants, 747 in the TIV group and 349 in the placebo group had blood drawn at 1 month following the last dose to assess antibody titers. The investigators then calculated the percentage of patients who achieved an immunologic postvaccination titer of at least 1:40 and geometric mean titers (GMT) in both groups.
In the TIV group, the percentage of patients achieving a serum neutralizing antibody titer of 1:40 or more to antigens H1N1, H3N2, and B was 50%, 86%, and 11%, respectively, compared with 7%, 10%, and 0.3% in the placebo group. With respect to GMT, the values for patients in the vaccine group for H1N1, H3N2, and B, respectively, were 33, 95, and 11 log2 compared with 7, 9, and 5 log2 for the placebo group, representing statistically significant increased antigen responses for all three strains in the vaccine group.
“In the TIV group, 90% achieved seroprotection to at least one strain of the virus, and 49.5% to at least two strains, compared to 16% and 0.9% in the placebo group,” Dr. Englund reported. “In reverse distribution curves, TIV is to the right of placebo in every case.”
In terms of safety, “there were no significant differences between the two groups in any of the outcomes we looked at,” noted Dr. Englund. Fever within 3 days of vaccination was seen in 11.2% of the TIV group and 11.7% of the placebo recipients, and serious adverse events were reported in 2.1% of the TIV group and 1.7% of the placebo patients. “Only one of the serious adverse events—a hypersensitivity reaction in a TIV patient that did not require hospitalization—was considered vaccine related,” she said.
Based on the results of the study, TIV demonstrated clear superiority to the current standard of care for infants younger than 6 months, Dr. Englund said. “Delivering the vaccine at the same time as routine immunizations is easy, safe, and enhances [influenza] protection in this very vulnerable population.”
Dr. Englund disclosed receiving research support for this investigation from Sanofi Pasteur Inc., manufacturer of Fluzone vaccine.
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