Introduction Nuvaxovid became available in Australia from February 2022, a year later than the first COVID-19 vaccines were released. It was a much-anticipated alternative vaccine for people that had either suffered an adverse event to and/or were hesitant to receive one of the mRNA or adenovirus based COVID-19 vaccines. Although safety from clinical trials was reassuring, small trial population size, relatively low administration rates worldwide and limited post-licensure intelligence meant potential rare adverse events were underinformed. Methods We conducted a retrospective observational analysis of adverse events following immunisation (AEFI) spontaneously reported to SAFEVAC, the integrated vaccine safety surveillance system used by Victoria and Western Australia, Australia. Reports received from 14 Feb 2022 to 30 June 2023 were analysed by vaccinee demographics, reported reactions and COVID-19 vaccine dose received and compared as reporting rates (RR) per 100,000 doses administered. Results 356 AEFI reports were received, following 102,946 Nuvaxovid doses administered. Rates were higher post dose 1 than dose 2 (rate ratio 1.5, p=0.0008); primary series than booster (rate ratio 2.4, p<0.0001); in females than males (rate ratio 1.4, p<0.01), especially those aged 30-49 years (RR=1.6, p=0.002). Serious AEFI included 76 chest pain (RR=73.8), two myocarditis (RR=1.9) and 20 pericarditis (RR=19.4). No cases of Guillain Barre or thrombosis with thrombocytopaenia syndromes were reported and no deaths attributable to vaccination. Conclusion The shared SAFEVAC platform enables pooling of clinically reviewed data across jurisdictions, increasing the safety profile evidence base of novel vaccines like Nuvaxovid and improving the odds for identification and description of rare events across all vaccines.

The authors have declared no competing interest.

Department of Health Victoria funds Murdoch Children's Institute to host and manage SAFEVAC for delivery of vaccine safety services in Victoria. The Department of Health Victoria has no access to data or role in analysis, writing or approval to publish. In WA this work is conducted as part of vaccine safety surveillance under the Public Health Act by WA public health servants.

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Ethical approval for this study was provided in Victoria as use of a registered database 36219 for public health surveillance and by the Chief Health Officer WA for provision of de-identified aggregated data informing public health surveillance. Permission to publish data from the Australian Immunisation Register was granted by Australian Government Department of Health and Aged Care.

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