(354) Real-world Nuvaxovid COVID-19 vaccine safety profile after first 100,000 doses in Australia

Background: Nuvaxovid became available for adults in Australia from early 2022, a full year later than the first COVID-19 vaccines. It was much-anticipated, as vaccine hesitancy of novel vaccine platforms amid fear of blood clots and cardiac inflammation attributed to the adenovirus-based and mRNA COVID-19 vaccines, had led to some people “waiting for Novavax”.

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 (AE) were underinformed.

Objectives: To describe AE reported following Nuvaxovid vaccination using population-based spontaneous surveillance data.

Methods: We conducted a retrospective observational analysis of adverse events following immunization (AEFI) spontaneously reported to SAFEVAC, the integrated clinical and epidemiological vaccine safety surveillance system used by Victoria and Western Australia—covering 9,163,517 population, approximately one-third of the Australian total. Reports received from 14 Feb 2022 to 30 June 2023 were analyzed by vaccinee sex and 10-year age group, reported AE reactions and COVID-19 vaccine dose number received. Stratified reporting rates (RR) per 100,000 doses administered, as recorded in the Australian Immunisation Register, were calculated.

Results: Almost half (48.3%) of the 102,946 doses administered were for primary series (dose 1 =25,496, dose 2 =24,183). Of 356 AEFI reports received (RR=345.8), rates were higher post dose 1 than dose 2 (rate ratio 1.5, p< 0.001), in females than males (rate ratio 1.4, p< 0.004) and overall in age group 40–49 years (RR=588.1).

Serious AEFI included 76 chest pain (RR=73.8), two myocarditis (RR=1.9) and 20 pericarditis (RR=19.4), all clinically confirmed. No cases of Guillain-Barré or thrombosis with thrombocytopenia syndromes were reported and no deaths attributable to vaccination.

Conclusions: Nuvaxovid, despite its late arrival, played a vital role in increasing COVID-19 vaccine uptake. Rates of cardiac inflammation presented similarly to the mRNA vaccines overall but were skewed toward the milder pericarditis. However, our data are not able to distinguish if this was a shift in clinical manifestation or reflecting a bias in persons receiving Nuvaxovid being more predisposed to—or aware of the need to report—heart inflammation symptoms.

Our multi-jurisdictional collaborative data model enabled clinical reviewed adverse event information in sufficient volume for meaningful insights. Post-licensure surveillance using real-world data is essential as we aspire to the 100 Days Mission of rapid vaccine deployment, to ensure safe immunization and maximize community confidence.