Whether co-administration of a COVID-19 and influenza vaccine leads to immune interference is unclear but possibly relevant for future vaccination programmes.
The international rollout of the COVID-19 vaccination programme is starting to break the link between infection and severe illness and hospitalisation. Whether or not an annual booster COVID-19 vaccination will be required in the future is yet to be determined. Nevertheless, in some countries, it is possible that the COVID-19 vaccination schedule could overlap with the influenza season, with a potential for an overlap in vaccine administration. As the Phase III COVID-19 vaccination trials excluded those who had a recent or planned receipt of another vaccine, there is a lack of data on the impact of co-vaccination. This led a team from the Novavax Institute, Gaithersburg, USA and St George’s University Hospital, London, UK, to consider the effect of simultaneous administration of the first dose of the NVX-CoV2373 (Novavax COVID-19 vaccine) and an influenza vaccination, in a subgroup of patients included in the Phase III efficacy trial of NVX-CoV2373. Subgroup patients were required to be in good health and not already received an influenza vaccination or any other live vaccine within 4 weeks. These individuals were randomised to receive a concomitant dose of influenza with their first NVX-CoV2373 dose or influenza and placebo. Although the main study was observer-blind, the influenza vaccine was administered in an open-label manner and reactogenicity was evaluated using an electronic diary for 7 days post-vaccination and the team assessed the antibody titres to both influenza and COVID-19 after 21 days.
Although the main trial recruited over 15,000 participants, only 431 were randomised to influenza vaccine or placebo. A total of 217 participants with a mean age of 39 years (43.3% female) and 75.1% of White ethnicity received the seasonal influenza vaccine and 214 received the influenza vaccine and placebo. Reactogenicity was more common in the co-vaccinated group compared to NVX-CoV2373 alone, with 70.1% versus 57.6% reporting tenderness, pain at the injection site (39.7% vs 29.3%), fatigue (27.7% vs 19.4%) and muscle pain (28.3% vs 21.4%). Although the influenza vaccine response was satisfactory, the COVID-19 vaccine efficacy was 87.5% in the co-vaccinated subgroup compared with 89.8% in the main group. The rates of adverse effects were low and balanced between those given NVX-CoV2373, influenza vaccine or both.
Commenting on these findings, the authors noted how this was the first direct evidence that co-vaccination still resulted in acceptable vaccine efficacy. While there was an increase in the reported incidence of local reactogenicity in the co-vaccinated group, symptoms were generally mild in severity. They concluded that the study had generated to early safety concerns over co-vaccination.
Toback S et al. Safety, immunogenicity and efficacy of a COVID-19 vaccine (NVX-CoV2373) co-administered with seasonal influenza vaccines. MedRxiv 2021