Not only is egg culture slower, but problems with the availability and cleanliness of eggs can hamper production, said Chen, a safety monitor in the U.S. trial. People who are allergic to eggs can also develop a reaction to egg residue in the vaccine.
Concern about a possible replay of the 1918-1919 flu pandemic has persisted since the late 1990s,. when an influenza strain infecting poultry in Hong Kong also spread lethally to humans. Since then, the virus has sickened 381 people - most of them in Southeast Asia and Indonesia - with a kill rate of more than 60 percent.
So far, the virus has not shown the capability of spreading rapidly from person to person, the much-feared ingredient for a pandemic. Most of the human victims caught the virus from chickens, with just a few contracting it from family members living in close quarters.
Though some experts have begun to wonder whether the virus will ever develop the ability to spread through human populations, many also concede that a simple genetic change may be all that's needed. Such a change could occur if the seasonal and so-called H5N1 avian influenza viruses infect someone at the same time and begin swapping genetic information.
"Scientists in influenza research continue to be concerned that this is something that may very well happen, and we just don't know when and how it's going to happen," said Dr. Neal Halsey, a professor at the Johns Hopkins Bloomberg School of Public Health and director of its Institute for Vaccine Safety.
"This is significant progress in making a vaccine that would help protect us from what appears to be a virus that could cause a pandemic," said Halsey, adding that cell-based manufacture is key to delivering a vaccine reliably and fast enough to meet an emergency.
jonathan.bor@baltsun.com
