Bird-flu vaccine effectiveness is limited but potentially useful

By Andrew Bridges WASHINGTON, AP

A bird flu vaccine that is even less effective than previously thought could still play an important role in protecting against the increased likelihood of a pandemic, a U.S. government health official said Tuesday.

A panel of federal health advisers was weighing whether to recommend government approval of the vaccine, made by Paris-based Sanofi Aventis SA.

The company believes the benefits of the vaccine outweigh its risks. The Food and Drug Administration said the vaccine is safe but it remains unclear whether it is effective.

In a clinical trial, the two-shot series appears to provide protection to just 45 percent of adults who received the highest dose. An earlier, interim analysis of the same study had suggested it prompted a protective immune response in 54 percent of patients, when measured 28 days after getting the second of two shots. Despite its limited effectiveness, the vaccine still could prove better than nothing in an outbreak, said Norman Baylor, director of the vaccine office at the FDA.

“The benefit of having a licensed vaccine against a potential pandemic influenza virus strain must be weighed against the risk of having no vaccine at the time of an inevitable influenza pandemic,” Baylor told the panel of experts. Baylor also said even a single dose of the two shot vaccine could help combat the deadly bird-flu strain called H5N1.

The FDA is asking its experts whether Sanofi provided enough data to back approval of its bird flu vaccine or if more are needed. The agency isn’t required to follow the advice of its advisory committees, but usually does. The vaccine is the first against the H5N1 influenza strain to seek FDA approval.

Effectiveness was measured by the antibodies patients developed against the flu strain. The results appear to fall well below what is expected of seasonal flu vaccines. Those regular flu shots, for example, protect 75 percent to 90 percent of vaccinated adults younger than 65.

The newer analysis used final data, while the earlier study used interim results, Sanofi said. The later analysis also used tougher standards to show the vaccine works, according to company documents released by the FDA.

The modest protective effects of the vaccine were seen in patients who received two 90-microgram doses of vaccine. The two shots contain 12 times the 15-microgram dose contained in regular winter flu shots.

Already, there are further studies under way that are looking at the use of immune boosters, called adjuvants, to try to improve the effectiveness of the H5N1 vaccine. Eventually, adjuvants also might shrink the needed dose for a pandemic vaccine closer to what is now used in seasonal shots.