Safety of SARS-CoV-2 XBB.1.5 and seasonal influenza vaccines co-administration: data from a perspective observational active surveillance study. Puglia (Italy), season 2023/2024.

Italian Ministry of Health recommended co-administration of influenza and SARS-CoV-2 vaccines for the 2023/ 2024 influenza season. Healthcare workers and students were identified as target categories for the vaccination campaign and the importance to implement pharmacovigilance programs was highlighted. We aimed to investigate the safety profile of mRNA SARS-CoV-2 vaccine (XBB.1.5), cell-based and egg-grown quadrivalent inactivated influenza vaccines (QIVc, QIVe) and the influence of co-administration on Adverse Events Following Immunization (AEFIs) via an active surveillance study. In this prospective observational cohort study, participants who received XBB.1.5, QIVc or QIVe, between October 17th-December 31st, 2023, either alone or in co-administration, were enrolled. AEFIs occurred in the first 7-days post-vaccination period were collected to investigate the reactogenicity profile of SARS-CoV-2 and influenza vaccines in co-administration or alone. 1014 HCWs completed the study follow-up. Of these, 34.12 % received co-administered influenza (QIVc or QIVe) and XBB.1.5 vaccine; 63.12 % either influenza vaccine alone (mostly QIVc) and only 2.8 % SARS-CoV-2 vaccine alone. The AEFIs reporting rate (RR) was 61.3/100 completed follow-ups (622/1014). The mostcommon AEFIs across all groups were injection site pain/itching and asthenia/malaise. Only 3 serious AEFIs occurred (RR0.30/100). Administration of XBB.1.5, either alone or co-administered with QIVe or QIVc, was associated with a higher risk of AEFIs (OR 4.82; 95 % CI 3.48–6.66; p < 0.001). Male sex was found to decrease the risk of AEFIs (OddsRatio 0.49; 95 %CI 0.37–0.65; p < 0.001). This study confirmed the safety profile of both SARS-CoV-2 and influenza vaccines, even when coadministered. However, healthcare authorities and policymakers should investigate HCWs concerns about SARS-CoV-2 vaccination and co-administration strategies.