Reygrobellet C, Viala-Danten M, Meunier J, Weber F, Nguyen VH.
An intradermal trivalent inactivated influenza vaccine administered using a microinjection system has received European marketing authorization from the European Medicine Agency. We assessed clinical trial subjects' perception of injection site reactions (ISRs) and whether ISRs affected overall acceptability of vaccination and willingness to be vaccinated in the future. A validated, self-administered, patient reported outcome questionnaire was completed 21 days after intradermal or intramuscular vaccination by elderly and non-elderly adult participants in two European randomized, controlled, open-label phase 3 trials. The questionnaire addressed: the acceptability of ISRs, effect of ISRs on arm movement or sleep, satisfaction with the injection system, and willingness to be revaccinated. Questions were answered using a 5-point Likert verbal rating scale (1 = most favourable, 5 = most unfavourable response). Mean scores were calculated per group. 5,305 questionnaires were completed and analysed (95% return rate). Mean scores were close to 1 in all cases (maximum 1.68), indicating an overall favourable opinion of the vaccination and ISRs. More than 96% of participants rated ISRs after intradermal or intramuscular vaccination as either 'totally acceptable' or 'very acceptable'. Willingness to get vaccinated the following year and satisfaction with the intradermal microinjection system or the conventional intramuscular syringe were high and were not adversely affected by ISRs. ISRs after intradermal influenza vaccine administered using a microinjection system are well accepted by the vaccinees and are generally not a cause for concern.