Others are developing vaccines that use only portions of the virus, and are thus easier to grow in cells. (Intact viruses can sometimes be toxic to both eggs and cell culture.) Nabel and his collaborators at NIAID’s Vaccine Research Center are developing DNA-based vaccines, in which circular pieces of DNA containing the virus’s HA gene are grown in bacteria. Researchers have already developed an H5N1 vaccine using this technology; it is currently in human trials. “We could have a vaccine ready to go into clinical trials in two to three months,” says Nabel. “But whether that will elicit the same magnitude of response as a conventional vaccine, or whether we have to do something to enhance that response, we don’t know.”
Ross and others are taking another approach: developing viruslike particles. “We take a set of genes from the virus and use it to generate a particle that looks like a virus but isn’t able to replicate,” says Ross. “The immune system reacts to it, even more robustly than it reacts to a traditional vaccine.” The advantage of this approach is that a candidate vaccine can be generated as soon as the viral sequence is available. “The H1N1 sequences are already on the Internet, so you can generate a vaccine even without access to the virus itself,” says Ross. “We will have a vaccine to test in preclinical trials in a few weeks.”
Many unknowns will affect how vaccine production proceeds in the coming months. The CDC still hasn’t decided whether to begin production of an H1N1 vaccine soon, or whether to hold off and include the H1N1 strain in next year’s seasonal flu vaccine. “We’re already working to ramp up the production of the seasonal flu vaccine so that, should we decide to manufacture a vaccine for the H1N1, we’d be able to do that,” said Richard Besser, acting director of the CDC, at a press conference earlier this week.
“We’ll be working very closely with the international community to understand what happens to this virus over the next few months as flu season begins in the Southern Hemisphere,” said Besser. “That will tell us a lot about whether the virus is changing, whether it’s becoming more severe, and what measures we might want to take in the fall.” For example, if the virus does mutate to become more deadly, it’s not clear that a vaccine made against the circulating strain would protect against the new strain.