Thimerosal-free seasonal flu vaccine exhibited similar immunogenicity as standard vaccine

Domachowske JB. Pediatr Infect Dis J. 2012;doi:10.1097/INF.0b013e31824e2924.

Issue: March 2012

A thimerosal-free trivalent seasonal influenza vaccine demonstrated comparable noninferiority results with vaccines containing thimerosal and exhibited similar immunogenicity and safety profile, according to a recently published study.

To limit mercury exposure in children from all sources — including the use of ethyl mercury-containing thimerosal as a vaccine preservative — researchers conducted a phase 3, observer-blind, randomized study in 30 centers in the United States from 2009 to 2010. Participants were randomly assigned to receive the study vaccine, a thimerosal-free trivalent inactivated influenza vaccine or a thimerosal-containing active comparator. Participants were also divided into one of three age categories: 3 to 4 years, 5 to 8 years or 9 to 17 years.

Each vaccine was administered as a 0.5 mL dose containing one of three recommended influenza strains: A/Brisbane/59/2007 (H1N1), A/Uruguay/716/2007 and B/Brisbane/60/2008.

Exclusion criteria for the study were:

Use of any investigational or nonregistered product (drug or vaccine) within 30 days preceding the administration of the study vaccine or planned use during the study period.
Receipt of a seasonal influenza vaccine outside of this study.
Receipt of systemic glucocorticoids within 1 month before study enrollment, or any other cytotoxic or immunosuppressive drug within 6 months of study enrollment.
Concurrent participation in another clinical study involving an investigational or a non-investigational product (pharmaceutical product or device).
History of hypersensitivity to any vaccine.
Acute disease or fever (>100.4°F) at the time of enrollment.
Administration of immunoglobulins or any blood products within the 3 months preceding the first dose of study vaccine or planned administration during the study period.
Pregnant or lactating female.
Any confirmed or suspected immunosuppressive or immunodeficient condition.

According to the study results, 2,116 children were vaccinated — 1,055 in the study vaccine group and 1,061 children in the control vaccine group — with no children withdrawn from the study due to adverse effects. The predefined noninferiority criteria and the Center for Biologics Evaluation and Research criteria for clinical benefit were met for all three seasonal virus strains in all children and each age strata.

The ratios of the adjusted geometric mean titers (control vaccine over study vaccine) ranged from 0.93 to 1.03 for the three virus strains, whereas the differences in seroconversion rate (control vaccine minus study vaccine) were between −2.42% and –1.6%. Post-vaccination geometric mean titers (range: 213.7-414.7 vs. 200.2-451.9) and seroconversion rates (range: 59.8%-81.1% vs. 58.2%-78.6%) were comparable for the two vaccines.

“The safety and reactogenicity profiles were comparable for the two vaccines for all children and for each age category,” the researchers said. “The incidence rates of local and general solicited symptoms were indistinguishable for the two vaccines in each age category, with pain at the injection site the most commonly reported symptom in all age strata.”

Disclosure: The researchers reported financial support from GSK Biologicals.

Stan L. Block

This article by Domachowske compares the immunogenicity and safety of a thimerosal-free GSK inactivated influenza vaccine with thimerosal-containing vaccine. Since thimerosal was added as a preservative to vaccines in very low quantity, one would expect that the thimerosal-free vaccine would have the same safety and immunogenicity as the thimerosal-containing product. This is indeed what the authors observed and this confirms that the thimerosal-free vaccine should be an effective and safe substitute for the older vaccine.

Steven B. Black, MD
Infectious Diseases in Children Editorial Board

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