Two stories have emerged on the influenza front, both dealing with potential vaccines — one specific to avian H5N1 flu and the other an all-around flu panacea.

U.S. government scientists say they have successfully tested in people a vaccine that they believe can protect against the strain of avian influenza that is spreading in birds in Asia and Russia. Health officials have been racing to develop a vaccine because they worry that, if the H5N1 strain mutates and combines with a human influenza virus to create a new virus, it could spread rapidly through the world.

Tens of millions of birds have died from infection and culling to prevent spread of the virus. As of Aug. 5 112 people have been infected, and 57 have died from the H5N1 strain of avian influenza. So far, there has been no sustained human-to-human transmission.

Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said that while the vaccine that has undergone preliminary tests could be used on an emergency basis if a
pandemic developed, it would still be several months before that vaccine is tested further and, if licensed, offered to the public. He cautioned: “We don’t have all the vaccine we need to meet the possible demand. The critical issue now is, can we make enough vaccine, given the well-known inability of the vaccine industry to make enough vaccine.”

Dr. Fauci has said that tests so far have shown that the new vaccine produced a strong immune response among the small group of healthy adults under age 65 who volunteered to receive it, although the doses needed were higher than in the standard influenza vaccine offered each year. The vaccine, developed with genetic engineering techniques, is intended to protect against infection, not to treat those who are sick.

Because the vaccine is made in chicken eggs, “a potential major stumbling block” to successful mass production is the number of eggs farmers can supply to vaccine manufacturers, Dr. Fauci said.

The additional tests are needed in part to determine the optimal dose of vaccine; how many shots people will need for protection; and whether adding another ingredient called an adjuvant to the vaccine could raise the potency of lower doses, stretching the number of people that could be protected. Even when these tests are completed, more time will be needed before the U.S. Food and Drug Administration can license the human vaccine and before policy makers determine when and how it should be administered.

The United States is thought to be the only country that has produced a human vaccine against the H5N1 influenza strain. Australia, Canada, France, Japan and the United Kingdom are among countries where scientists are trying to develop human avian influenza vaccines, according to the World Health Organization.

In the United Kingdon, scientists are making a vaccine that could provide lifelong protection against all types of flu in a single vaccination. Currently, at-risk people in the UK — the elderly and ill — need annual flu shots, and there is no vaccine available yet guaranteed to beat avian influenza. Biotechnology firm Acambis, in Cambridge, U.K., says it hopes its vaccine will target numerous mutations that presently allow flu to evade attack. However, the work is very early and is years away from being tested in humans.

Each year, winter flu kills around 4,000 people in the U.K. Globally, between 500,000 and 1 million people die each year from influenza. If the avian influenza virus currently circulating in Asia were to mutate and spread from person to person, it could kill as many people as the 1918 Spanish flu, which claimed between 20 and 40 million lives.