Smallpox, a disease caused by variola virus, has been globally eradicated since the early 1980s due to the massive vaccination program conducted by the World Health Organization. However, there are concerns that the smallpox virus could be used as a biological weapon. In addition, the monkeypox virus, which resembles the smallpox virus, is an emerging virus that caused an outbreak of human monkeypox in Africa, and more recently in the United States. Therefore, the need for protection against these zoonotic viral infections remains [1-3].
Variola belongs to the Orthopoxvirus genus, family Poxviridae, which also includes vaccinia, monkeypox, cowpox, and other viruses. Because the majority of orthopoxvirus DNA is highly conserved considerable cross-protection can be conferred, through infection or immunization, within this family of viruses. For example, variola virus shares >90% similarity with the vaccinia genome, which enabled eradication of smallpox using the vaccinia virus. …show more content…
Dryvax was a first-generation smallpox vaccine, and one of the vaccines used during worldwide eradication of smallpox. This vaccine was prepared by harvesting live vaccinia virus from lesions on the skin of infected cows. Although Dryvax was highly effective, it had adverse side effects including fever, headache, and myalgia. More serious side effects included generalized vaccinia, eczema, encephalitis, and even fatality [7,8]. Later, a second-generation vaccine, ACAM2000, was developed, focusing on cell culture methods for vaccine production. In terms of immunogenicity, this vaccine had comparable immunogenicity to that of the first-generation vaccine. However, ACAM2000 still had serious adverse events such as cardiac complications [9]. To overcome the side effects caused by the use of live-virus vaccines, protein- or DNA-based subunit vaccines are currently under investigation