From Wikipedia:

A chimera virus is defined by the Center for Veterinary Biologics (part of the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service) as a “new hybrid microorganism created by joining nucleic acid fragments from two or more different microorganisms in which each of at least two of the fragments contain essential genes necessary for replication.”^[1] The term chimera already referred to an individual organism whose body contained cell populations from different zygotes or an organism that developed from portions of different embryos. In mythology, a chimera is a creature such as a hippogriff or a gryphon formed from parts of different animals, thus the name for these viruses. Chimeric flaviviruses have been created in an attempt to make novel live attenuated vaccines.^[2]

As a bioweapon

Combining two pathogenic viruses increases the lethality of the new virus^[3] which is why there have been cases where chimeric viruses have been considered for use as a bioweapon. For example, the Soviet Union’s Chimera Project attempted to combine DNA from Venezuelan equine encephalitis, smallpox and Ebola virus in the late 1980s^[4]. A combination smallpox and monkeypox virus has also been studied^[3].

References

• Center for Veterinary Biologics Notice No. 05-23. USDA website. Dec.8, 2005
• Lai, C. J; Monath, T. P (2003). “Chimeric flaviviruses: novel vaccines against dengue fever, tick-borne encephalitis, and Japanese encephalitis”. Adv Virus Res. Advances in Virus Research. 61: 469–509. doi:10.1016/s0065-3527(03)61013-4. ISBN 9780120398614. PMID 14714441.
• Collett, Marc S. (2006). “Impact of Synthetic Genomics on the Threat of Bioterrorism with Viral Agents”. Working Papers for Synthetic Genomics: Risks and Benefits for Science and Society: 83–103.
• Ainscough, Michael J. (2004). “Next Generation Bioweapons: Genetic Engineering and BW”.
• Lulla, Premal D.; Hill, LaQuisa C.; Ramos, Carlos A.; Heslop, Helen E. (2018). “The use of chimeric antigen receptor T cells in patients with non-Hodgkin lymphoma”. Clinical Advances in Hematology and Oncology. 16 (5): 375–386. PMC 6469642. PMID 29851933.
• US Grant US10053493B2, William Messer; Aravinda De Silva & Boyd Yount, “Methods and compositions for dengue virus vaccines”, published 2014, issued 2018, assigned to University of North Carolina at Chapel Hill