Researchers found a lower rate of pediatric fever after applying a standard definition of fever across three different clinical trials of pediatric patients receiving influenza vaccinations, according to research published in the Pediatric Infectious Disease Journal.
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Investigators in future studies must adopt a standardized definition of pediatric fever after an influenza vaccination. “Our study demonstrates the variability in results which occur due to minor differences in the definition of fever, methods of analysis and reporting of results,” Jean Li-Kim-Moy, MBBS, of the University of Sydney, and colleagues wrote.
Dr. Li-Kim-Moy and colleagues analyzed pediatric datasets from three different clinical trials using trivalent influenza vaccine (TIV); the primary trial included 3,317 children aged 6-35 months who were randomized to receive Fluarix at 0.25 mL or 0.5 mL, or receive 0.25 mL of Fluzone. The other two trials studied children receiving TIV between 6 months–17 years and 3-17 years. The researchers also performed a multivariable regression analysis to determine the relationship between immunogenicity, antipyretic use, and postvaccination fever.
The primary study initially reported the fever rate 0 days–3 days after vaccination was between 6% and 7%. After reporting the rate of fever separately for each dose and changing the criteria to “defining fever as greater than or equal to 38.0°C by any route of measurement” for the primary study, the researchers found a rate of any-cause fever was 3%-4% for the first dose and 4%-5% for the second dose. The rate of vaccine-related fever in the primary study was 3% for the first dose and 3%-4% for the second dose, with researchers noting vaccine-related fever occurred significantly earlier compared with any-cause fever (mean 1 days vs. 2 days after vaccination; P equals .04).
Impact of fever, antipyretics
The researchers also performed a pooled immunogenicity analysis of 5,902 children from all three trials and found a strong association between fever after vaccination and increased geometric mean titer (GMT) ratios (1.21-1.39; P less than or equal to .01) and an association between antipyretic use and reduced GMT ratios (0.80-0.87; P less than .0006).
“Our pooled analysis of the three trials demonstrated highly significant associations, for all strains, between postvaccination fever and up to 39% higher GMT; Similarly, strong evidence of associations in the opposite direction was found between postvaccination antipyretic use (days 0-3), adjusting for all other factors including fever, and decreased immunogenicity against all vaccine strains in children,” Dr. Li-Kim-Moy and colleagues said.
Antipyretic use was common in the primary study, occurring in one in six of the children, they said. These findings of “significant associations between fever and increased vaccine immunogenicity, and between antipyretic use and reduced immunogenicity in children after influenza vaccination” suggest the need for further study, especially because parents often give antipyretics if their children are febrile after vaccinations.
“There is uncertainty whether our findings, and those of others, on immunogenicity translate into clinically significant effects,” they wrote. “However, the fact that influenza vaccine, unlike many routine childhood vaccines, is only moderately protective may mean that modest reductions in antibody response are more likely to correlate to less protection.”