New bird flu vaccine promises broad immunity and rapid manufacture

Medical Tribune August 2008 SFXII
David Brill

A new vaccine against the avian influenza H5N1 virus has been shown to be well tolerated and induce high levels of immunogenicity against a variety of strains.

The vaccine is derived from continuous cell culture and could be produced up to 3 months quicker than by using traditional methods, the manufacturers suggest.

Mr. Peter Carrasco, Policy Advisor on Vaccine Security for WHO, said that the vaccine could be useful for protecting against viruses that are currently circulating in infected birds, but added that more research is needed with larger study groups to reconfirm the trial’s findings.

The vaccine was tested in a randomized phase I and II trial involving 275 subjects who received two doses 21 days apart. The results were published in The New England Journal of Medicine.

A dosage of 7.5 mcg without adjuvant induced a neutralizing-antibody response in 76.2 percent of subjects – equivalent to a seroconversion rate of 69 percent. Immunogenicity was seen not only against the clade 1 strain used to produce the vaccine (A/Vietnam/1203/2004), but also extended to the clade 2 and 3 strains.

Conventional H5N1 vaccines are produced using embryonated chicken eggs – a technique that requires the use of an attenuated version of the virus. Cell culture, however, can be used to generate a vaccine from the wild type, thereby eliminating the delay while a modified virus is produced.

“The lag time between receipt of a new virus and delivery of a new vaccine is only something like 12 weeks using our technology, which is about 3 months quicker than can be done with the egg technology,” said Dr. Noel Barrett from the Department of Global Research and Development at Baxter BioScience, who developed the vaccine.

“We’re faster, we’re more flexible, and the process is much more robust in that we’re not dependent on the supply of hen’s eggs, which is an uncertain factor in the event of a pandemic caused by an avian virus.”

Baxter have submitted a licensing application for the vaccine to the European Medicines Agency (EMEA), and expect a decision early next year.

The company has reached agreements with some countries to provide the vaccine in the event of a pandemic and already has the manufacturing capacity to deliver in a relatively short time, Barrett said. The decision whether to implement pre-pandemic vaccination remains a matter of government policy, he added.

One potential drawback to the new vaccine is the need for enhanced biosafety facilities which can handle the virulent wild type virus.

“There are very few facillities which are biosafety level 3, and these are expensive to maintain,” said Associate Professor Paul Ananth Tambyah, head of the Division of Infectious Diseases at the National University Hospital in Singapore, who was also one of the authors of the study.

“Without them it is not safe to manufacture this vaccine,” he said, adding that these manufacturing hurdles would need to be overcome before the vaccine could be used routinely.