(C-253) Active and Passive Safety Surveillance in Children Receiving Fluenz® Tetra Vaccination in England During Influenza Seasons - from 2014/2015 to 2022/2023

Background: Fluenz® Tetra is a quadrivalent, live attenuated, intranasal, influenza vaccine (qLAIV) recommended for use in children aged 2 to 17 years vaccinated as part of the seasonal influenza immunisation campaign in the UK. This abstract compares results across the 2014/2015 active surveillance season and the subsequent eight passive Enhanced Safety Surveillance (ESS) seasons (2015/2016-2022/2023).

Objectives: To compare and describe the safety of qLAIV in children during nine influenza seasons in England.

Methods: Active surveillance was conducted in 2014/2015. Vaccinees were recruited via England’s vaccination programme which offered the vaccine to children aged 2-4 years + others at high risk. Vaccinees or their representatives were asked to complete questionnaires at enrolment and 14 days post-vaccination, irrespective of whether they experienced an adverse event (AE). Over subsequent seasons, vaccine roll-out was expanded to include children up to 16 years. For these seasons, passive ESS was conducted and involved distributing Safety Report Cards (SRCs) at GP practices or schools for children or their representative to return if any adverse drug reactions (ADRs) occurred. The number of SRCs distributed was recorded, and this was used as the denominator for calculating risk estimates. The studies received approval from NHS Research Ethics Committees.

Results: For active surveillance (2014/2015), 385 eligible vaccinees were recruited. The most common AE of interest was nasal congestion (43.4%), followed by malaise (22.6%) and cough (20.8%). No serious AEs were reported.

For passive ESS (2015/2016-2022/2023), 8,753 to 17,922 SRCs were issued per season. The highest return rate for eligible SRCs was in 2015/2016 (1.9%,), declining to 0.4% in 2022/2023. In all seasons, rhinorrhoea was the most frequently reported ADR (range 0.1%-0.6% of SRCs issued). Serious ADRs were rare ( < 1 in 1000 SRCs issued) in all seasons. Passive ESS relied on spontaneous reports, possibly leading to the underreporting of ADRs. This methodological difference, compared to active surveillance, may be reflected in the lower incidence observed in passive ESS.

Conclusions: The 2014/2015 active surveillance study for qLAIV showed no safety signals from the data collected. From 2015/2016-2022/2023, the number of ADRs remained low, were typically non-serious, with serious ADRs rarely reported. The pattern and frequency of ADRs were consistent across seasons. The active surveillance and passive ESS have provided additional valuable pharmacovigilance activities, supporting the positive benefit-risk balance of qLAIV in children. The 2022/23 season was the final season of passive ESS following Pharmacovigilance Risk Assessment Committee (PRAC) recommendation.