Hazard Characterization of Modified Vaccinia Virus Ankara Vector: What Are the Knowledge Gaps?

Okeke, Malachy I.; Okoli, Arinze S.; Diaz, Diana; Offor, Collins; Oludotun, Taiwo G.; Tryland, Morten; Bøhn, Thomas; Moens, Ugo

The MVA vaccine against smallpox was administered mostly intradermally or subcutaneously. It was often used in Germany from 1968 to 1988 as a first vaccination, usually to vaccinia-naive children and adults that could be at risk for adverse effects if vaccinated with other and less attenuated smallpox vaccines [53] . The MVA vaccine elicited a weak virus neutralizing antibody response, as a first priming of the immune system, which was followed by a VACV smallpox vaccination resulting in an effective immune response and protection against smallpox. However, it was later discovered that the weak neutralizing antibody elicited by MVA priming is because the hemagglutinin (HA) protein to which VACV antibody neutralizing assay is based on is absent in MVA. This is due to the truncation of the HA promoter [46] . As a response to MVA, vaccinees experienced mild local reactions such as reddening on the vaccine inoculation site, but did not develop blisters, pustules or ulcers. Of 7098 vaccinees, 2.3% developed fever (i.e., >38 • C) and 4.1% developed non-specific general symptoms [53] . The MVA vaccine was licensed in Germany in 1977 and was administered to over 120,000 persons. However, these vaccinations were conducted when smallpox was no longer endemic in Germany and thus its immunological efficacy against a fully virulent VARV remains unknown [54] , but it has proven to protect primates from lethal monkeypox infection [55] .