Febrile events including convulsions following the administration of four brands of 2010 and 2011 inactivated seasonal influenza vaccine in NZ infants and children: the importance of routine active safety surveillance.

OBJECTIVE

To evaluate and compare rates of febrile events, including febrile convulsion, following immunisation with four brands of inactivated 2010 and 2011 influenza vaccine in NZ infants and children.

METHODS

Retrospective telephone surveys of parents of infants and children who received at least one dose of the vaccines of interest.

METHODS

184 NZ General Practices who received the vaccines of interest.

METHODS

Recipients of 4088 doses of trivalent inactivated vaccines Fluvax(®), Vaxigrip(®), Influvac(®) and Fluarix(®) and/or monovalent Celvapan. Vaccinees were identified via the electronic Practice Management System and contacted consecutively.

METHODS

Primary outcome was febrile convulsive seizure. Secondary outcomes were presence of fever plus other organ system specific symptoms.

RESULTS

The parental response rate was 99%. Of 4088 doses given, 865 were Fluvax(®), 2571 Vaxigrip(®), 204 Influvac(®), 438 Fluarix(®) and 10 Celvapan. Three febrile convulsions followed Fluvax(®), a rate of 35 per 10,000 doses. No convulsions occurred following any dose of the other vaccines. There were nine febrile events that included rigors, all following Fluvax(®). Fever occurred significantly more frequently following administration of Fluvax(®) compared with the other brands of vaccines (p<0.0001) and Fluvax recipients were more likely to seek medical attention. Influvac(®) also had higher rates of febrile reactions (OR 0.54, 0.36-0.81) than the other two brands Vaxigrip(®) (OR 0.21, 0.16-0.27) and Fluarix(®) (OR 0.10, 0.05-0.20). After multivariable analysis vaccine, European ethnicity and second dose of vaccine were significantly associated with reporting of fever within 24h of vaccination.

CONCLUSIONS

Influenza vaccines have different rates of reactogenicity in children which varies between ethnic groups. High rates of febrile convulsions and reactions in children receiving Fluvax(®) and to a lesser extent the higher fever rates in those receiving Influvac(®) compared with the other two brands of influenza vaccines in this study suggests that reactogenicity profiles need to be considered prior to national policy advice each season. The risk-benefit profile in children might not be equally favourable for all licensed paediatric influenza vaccines. More attention needs to be given to comparative research for all trivalent seasonal vaccines, and with all strain changes.