Outbreaks of avian influenza (the “bird flu”) among birds have occurred in more than 30 countries. As of March 10, 2006, there have been 176 confirmed cases of the bird flu in humans worldwide, and 55% of those infected have died. Some experts fear that a severe bird flu pandemic could result in two million deaths in the US alone. The bird flu has not reached pandemic proportions to date, because the virus cannot yet be efficiently transmitted from human to human. But in the event that it does evolve this capability, researchers are looking for a safe and effective bird flu vaccine that could be quickly manufactured on a very large scale.

In a new study in the March 30, 2006 issue of the New England Journal of Medicine , researchers compared different doses of a bird flu vaccine in healthy adults. They found that the highest dose of the vaccine was safe and relatively effective. But it may not be feasible to manufacture this high dose on a large scale.

About the Study

This study included 451 healthy adults ages 18-64. They were randomly assigned to receive two doses of a bird flu vaccine containing 90, 45, 15, or 7.5 micrograms of the bird flu antigen (which stimulates the production of antibodies), or a placebo, administered 28 days apart. After an additional 28 days, the researchers analyzed the participants’ blood samples to determine who had developed an acceptable response (i.e., concentrations of bird flu antibodies high enough to be considered protective against the virus).

All doses of the vaccine were determined to be relatively safe; the most common adverse event being mild pain at the injection site. Doses of 90, 45, 15, and 7.5 micrograms resulted in acceptable responses in 54%, 43%, 22%, and 9% of the participants, respectively. The placebo did not result in any response.

This study is limited because it did not test the safety and effectiveness of the vaccine on elderly people, people with impaired immunity, or children. There is also no way of knowing whether the best antibody responses observed in this study will be sufficiently protective during an actual flu pandemic.

How Does This Affect You?

These findings suggest that two 90-microgram doses of the bird flu vaccine tested in this study were safe and somewhat effective. But with the current manufacturing capacity, only about 1.25% of the world’s population could be immunized if the dose requirement were this high.

Where do we go from here? The vaccine in this study did not contain an adjuvant (an agent that increases the response to the vaccine), and vaccines with an adjuvant may require less antigen, increasing the number of people who could be immunized. Another major concern is that by the time the virus evolves enough to produce a human pandemic, it may completely impervious to this particular vaccine. The US government is funding the development and testing of more than 30 bird flu vaccines, with the hope of finding a safe, effective one that can be stockpiled and ready to deploy in the case of a worldwide pandemic. Unfortunately, there is no guarantee of success.