The common, replicating measles vaccine virus is highly immunogenic and one of the safest live attenuated vaccines worldwide. Recombinant measles vectors can be used to deliver pathogen-specific antigens (e.g. from a coronavirus) to induce pathogen-specific vaccination effects.

SARS-CoV-2 is a coronavirus that newly emerged in late 2019 in China. The virus causes a new severe acute respiratory syndrome (SARS) referred to as COVID-19. SARS-CoV-2 is highly contagious and was declared pandemic by the WHO on 11th of March 2020. By June 2020, more than 6,000,000 people in about 200 countries were infected and more than 380,000 infection-related deaths were reported. There is no known vaccine or antiviral treatment available. The safety and long-term efficacy of many vaccine candidates in development are unknown. Governments across the world forced people into quarantine and issued preventive measures to contain the pandemic. This caused a major global social and economic disruption that led to a deep global recession.

Our measles vaccine vector encoding SARS-CoV-2 antigen has been shown to induce effective cellular and humoral immune responses and may qualify for protection against COVID-19. Balancing immunogenicity and tolerability is key to develop vaccines that are effective and safe. For COVID-19, using a replicating attenuated coronavirus would be highly immunogenic but bears a potential risk of residual pathogenicity. Using an alternative virus vector system with a defined safety profile, e.g. a measles vaccine backbone, to deliver coronavirus-specific antigens eliminates this potential risk but maintains the quality of a multifunctional immune activation.