Hamburg and Oxford - While there is an urgent search for an effective vaccine against the new coronavirus SARS-CoV-2, 2 vaccine candidates against the related MERS-CoV have proven to be safe in phase 1 studies. The results published in Lancet Infectious Diseases (2020; DOI and) also document an immune response against the virus.
Of the 3 coronaviruses that can cause fatal infections, MERS-CoV is the most dangerous. Of the 2,519 diseases known to date, 866 were fatal, resulting in case fatality rate of 34.3%. Most diseases occur in Saudi Arabia, where dromedaries form the natural reservoir. However, the 2014 outbreak in South Korea, where 186 people fell ill and 38 died, shows that MERS has the potential for pandemic.
The current situation with COVID-19 shows how important vaccine would be that could be produced quickly in an emergency. 2 research teams have now completed the first clinical tests for 2 MERS vaccines.
Both vaccines use harmless virus as vehicle. Sarah Gilbert's research group from Oxford University deals with the ChAdOx1 variant of an adenovirus that circulates in chimpanzees and that is not able to replicate. It was equipped with the spike protein of the MERS-CoV.
The team around Marylyn Addo from the University Medical Center Hamburg-Eppendorf () uses vaccine based on the modified Vaccinia Ankara Virus (MVA), the was originally developed as smallpox vaccine. To convert it into MERS vaccine, it was also equipped with the spike protein from MERS-CoV.
The two vaccine viruses are known to be safe. The two phase 1 studies examined whether this is still the case after being equipped with the spike protein. In Oxford, 24 healthy volunteers received single vaccination, with increasing doses being tested. In Hamburg, 26 healthy volunteers were vaccinated, with 2 vaccinations being planned. Here, too, the vaccine dose was slowly increased in the course of the study in order to explore possible limits of tolerability.
Both vaccines passed the safety test. Both got an immune response. It is still unclear whether it is sufficient to protect people from infection. The ChAdOx1-MERS vaccine achieved an antibody response that was still detectable even after 180 days in 18 of 24 patients (75%). On day 364, 13 of 29 participants were still protected. The MVA-MERS vaccine appears to be little weaker. Only 3 of 22 test subjects (14%) still had detectable antibody titers after 180 days.
Both groups want to continue developing their vaccine. It would probably not be effective against SARS-CoV-2. Both viruses enter the cells via different receptors. MERS-CoV uses the DPP4 receptor, while SARS-CoV-2 docks with the ACE2 receptor.