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Aug 15, 2005
 |  BioCentury  |  Product Development

A curate's egg

Clinical data announced last week suggest that a vaccine developed by sanofi Pasteur may offer some protection against the H5N1 avian influenza virus in the event of a pandemic. However, the amount of antigen required to induce an immune response will put additional pressure on already limited egg-based manufacturing capacity. Companies are stepping up their efforts to provide alternative approaches. But the challenge is huge and there will be no quick fixes on either the vaccine or antiviral fronts.

Flu vaccines are still prepared using a method developed more than 50 years ago: viruses are grown in fertilized chicken eggs, harvested, chemically inactivated and then processed into vaccines. Delivery of the final product can take more than six months, and capacity is limited by the ability of eggs to produce a maximum of three doses each.

Given the vaccine shortages of the past couple of flu seasons, the concern for public health authorities is that if producers are struggling to meet demand from normal flu seasons, they may buckle under a surge in demand from a pandemic. This is especially so if the avian virus kills chicken embryos and destroys chicken populations.

Scaling up

Last November, the U.S. Department of Health and Human Services (HHS) awarded sanofi Pasteur (Swiftwater, Penn.) a contract to ensure year-round availability of an increased egg supply.

Meanwhile, the National Institute of Allergy and Infectious Diseases (NIAID) has contracted for pilot lots of candidate pandemic vaccines from sanofi Pasteur and Chiron Inc. (CHIR, Emeryville, Calif.). Last week, NIH unveiled preliminary results from a trial in healthy volunteers showing that two large doses of the sanofi Pasteur vaccine might offer protection against the strain of avian influenza that is spreading through Asia and is reported to have gotten into Russian flocks.

In 115 subjects, two 90 µg shots of flu antigen were required to trigger an immune response likely to confer protection. The trial will enroll 452 subjects.

"Although we are extrapolating what we saw in the first 100 or so patients, we believe the antibody levels we have seen would probably be enough to provide protection. We saw a dose response and noted that it appears that the vaccine was well tolerated," John Treanor, principal investigator of the tests conducted at the University of Rochester, told BioCentury.

To produce its vaccine against the H5N1 strain, sanofi Pasteur used reverse genetics, removing a gene that made the virus deadly to birds. The modified virus could then be grown in chicken...

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