A combined hepatitis A and typhus vaccine (Vivaxim, Sanofi-Aventis) licensed in Australia for use in patients aged > 16 years was shown to be well-tolerated in children aged 2 to 16 years, according to a brief report in the Journal of the Pediatric Infectious Diseases Society.

Vivaxim has been available in Australia since 2006 and is used “off-label” in children aged 2 to 16. According to investigators, only one study to date has investigated adverse events following immunization with Vivaxim in children aged 2 to 16 years, concluding that it was safe and well tolerated. This study, however, lacked a control, so investigators aimed to study Vivaxim’s safety and tolerability in children by directly comparing adverse events following immunization with concurrent monovalent vaccines in Australian primary care and travel medicine clinics.

In total, 7786 children aged 2 to 16 who received Vivaxim or concurrent monovalent hepatitis A (Avaxim, Havrix 1440, Havrix Junior, Vaqta adult, Vaqta pediatric) and typhoid(Typherix, Typhim Vi) vaccines between April 16, 2015, and July 1, 2019, at participating clinics in Australia that usedSmartVax were included in the study. SmartVax is a monitoring system for adverse events following immunization that collects data via SMS from the parents and guardians of vaccine recipients and integrates it with clinical data extracted from commercially available medical practice management software.

Of the included children, 1315 received Vivaxim and 6471 received concurrent monovalent vaccines. Demographic differences between the 2 groups included that Vivaximrecipients were more commonly girls (55.5%) and older (aged 14 years), whereas, recipients of monovalent vaccines were slightly more commonly boys (51.1%) and younger (aged 8 years). Also, those in the Vivaxim group were older (14 years;interquartile range, 8-16 years), and those in the monovalent group younger (8 years; interquartile range, 4-11 years; P< .001).


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The percentage of children who experienced adverse events following immunization was similar in both groups: 2.9% for Vivaxim and 3.3% for concurrent monovalent vaccines (P = .469). Percentages of reported local (1.2%) and systemic (1.1%) reactions were also similar in both groups. The most common local reactions in both groups were pain (1.1%)and swelling (0.4%); tiredness/fatigue (0.7%) and fever(0.6%) were the most commonly reported systemic reactions. After adjusting for sex and age group, the odds of an adverse events following immunization (odds ratio [OR], 0.96; 95% CI, 0.66-1.39), local reaction (OR, 0.93; 95% CI, 0.52-1.66), and systemic reaction (OR, 0.90; 95% CI, 0.49-1.66) for those receiving Vivaxim were similar to the children that received monovalent vaccines.

Although the study adds to the evidence on vaccination options for children, investigators noted several limitations. These included that the response rate for SmartVax ranges between 70% and 74% and parents or guardians of children who experience adverse events following immunization may be more likely to respond. This could lead to an overestimation of the percentages of patients who experienced adverse events following immunization, but response rate is unlikely to be associated with type of vaccine. Also, severity of adverse events following immunization, follow-up information after an adverse event, and whether the monovalent vaccines were administered in the same arm or different arms were not available in the dataset. Furthermore, the indication and designation of symptoms relied on self-assessments from both children and/or their caregivers.

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Investigators concluded that this work found no evidence of increased overall risk for adverse events following immunization, local reaction, or systemic reactions with Vivaxim. They also encouraged healthcare providers to discuss Vivaxim as an option with parents and guardians while advising them that it is an off-label use. Further research is still needed to investigate the immunogenicity of Vivaxim in children against the monovalent vaccines and to assess possible delayed adverse events in this age group.

Reference

Furuya-KanamoriL, Dutton P, Leeb A, Mills DJ, X Andrews R, Lau CL. Adverse events following immunization with combined vs concurrent monovalent hepatitis A and typhoid vaccines in children [published online April 25 2020]. J Pediatric Infect Dis Soc. doi:10.1093/jpids/piaa031