NEW YORK (Reuters Health) - Modified vaccinia Ankara is a leading candidate for an alternative smallpox vaccine, according to researchers at the National Institutes of Health.
In the June 15th issue of Clinical Infectious Diseases, Dr. Lewis H. McCurdy and colleagues at the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland review alternatives to the currently available vaccine against smallpox. The present Dryvax vaccine, they note, “is associated with side effects that are difficult to accept in a vaccine for a disease that has not been present for more than 25 years.”
The team points out that as early as the 1970s, German researchers discovered in large-scale human studies that vaccination with modified vaccinia Ankara, a poxvirus vaccine, is well tolerated and protects against subsequent intradermal challenge with replication-competent vaccinia. Because smallpox had been eradicated from Europe by then, however, modified vaccinia Ankara was never field-tested.
More than 120,000 subjects were safely vaccinated by various routes in the German trials. These included children and elderly individuals and patients with skin conditions. There were no serious adverse events, even in subjects at increased risk for complications.
Furthermore, when vaccinees were revaccinated with Elstree vaccinia weeks to months later, the German researchers observed an attenuated response that was indicative of prior immunity.
“Focus on the development of a safer vaccinia vaccine has been heightened with the emerging threat of bioterrorism,” the researchers point out. Modified vaccinia Ankara, they say, has “a profile that appears optimal for vaccine development - diminished virulence and enhanced immunogenicity.”
Clinical trials to determine the safety, immunogenicity, and optimal dosing of modified vaccinia Ankara vaccines are underway. However, licensure is likely to be problematic “because of the inability to define efficacy in the absence of natural disease.”
Although the agent “is a promising vaccine candidate for safely inducing and maintaining immunity against orthopoxviruses,” the researchers conclude, “our hope remains that protection against a smallpox outbreak will never be necessary.”
Source: Clin Infect Dis 2004;38:1749-1753. [ Google search on this article ]
Copyright © 2002 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.