In the study, investigators divided 24 cynomolgous monkeys into four groups. Group 1 received two injections of MVA, two months apart; Group 2 received one injection of MVA followed by inoculation with Dryvax two months later; Group 3 received nothing at baseline and one Dryvax inoculation two months later; and Group 4 served as the unimmunized control group.

Following the MVA and Dryvax immunizations, the team measured the immune responses of the monkeys. Results showed that after two doses of MVA or one dose of MVA followed by Dryvax, the animals' immune responses were equivalent to or higher than those induced by Dryvax alone.

Two months after the last immunization, each of the 24 monkeys was challenged by intravenous injection of monkeypox virus. The unvaccinated animals became ill or died, showing signs of fever, pox lesions, weight loss, and reduced activity. The vaccinated animals were healthy overall, though minor skin lesions were seen in the group that received MVA alone and were then challenged.

According to the authors, MVA has potential use as a replacement for Dryvax, given that the immune responses elicited by one or two doses of MVA approach those of the licensed product. In addition, MVA could be useful as a pre-vaccine to Dryvax, reducing the local reaction to a subsequent smallpox vaccination without diminishing the total immune response. Further studies are planned to determine the longevity of protection, the dosage effects, and other factors.

"This work is the result of a productive collaboration between federal and academic partners," said Colonel Erik A. Henchal, commander of USAMRIID. "These are the relationships that will, in the future, deliver the biodefense products the nation needs."

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Contact: Caree Vander Linden
Caree.Vander-Linden@amedd.army.mil
301-619-2285
US Army Medical Research Institute of Infectious Diseases
10-Mar-2004