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Researchers Prepare for Possible Swine Flu Vaccine

Richard Besser, the acting head of the U.S. Centers for Disease Control and Prevention, said Tuesday that the CDC is readying seed stock should the decision be made to ramp up production on a swine flu vaccine. “Seed stock” is a stock of the strain of virus that could be distributed to vaccine manufacturers.

“Right now we don’t have a vaccine that can treat this strain of flu,” Besser said. “We’re are growing up that seed stock of virus so that … if a decision is made that we need to rev up production to make that vaccine we would be ready to do so.”

Besser has repeatedly told reporters that the decision to create a vaccine is not an easy one to make and that discussions are ongoing. Richard Compans, director of the Emory Influenza Pathogenesis and Immunology Research Center in Atlanta said he believes that step will be taken.

“I think it is already likely that it will go forward,” said Compans. “The virus has spread much more widely and more rapidly than the H5 avian virus for which a vaccine was prepared, therefore I think it’s likely it will be done with the swine virus.”

But Compans said that even if the decision is made it would still take months to produce, because current methods of developing and manufacturing vaccines take time.

Each year, vaccine manufacturers produce a seasonal flu vaccine that protects against the three strains of the flu predicted by the Food and Drug Administration to be most prevalent for the next year’s season. The CDC creates a seed stock of those strains which it distributes to manufacturers, who are responsible for growing it up into large batches and developing it for human testing.

The strains for next year’s vaccine were selected about five weeks ago, and a decision to include the swine H1N1 strain could mean removing another strain that was deemed necessary for the vaccine.

Dr. Andrew Pekosz, an associate professor of molecular microbiology and immunology at Johns Hopkins University, stressed that manufacturing capacity is the most important limiting factor when looking at development of the vaccine.

“We cannot grow up an endless number of influenza viruses for vaccine purposes … there are three components in the standard flu vaccine and it is very difficult to grow up four components because of the availability of eggs and other agents,” said Pekosz.

Chicken eggs are used by vaccine manufacturers, who inject seed virus into the egg, where it is incubated and multiplies. Other, more experimental, methods of creating vaccines do exist, but Pekosz said that everything known about the swine H1N1 strain suggests it should be possible to generate an effective vaccine in the same way that a seasonal vaccine is created.

“I think the safest way to move forward is using the techniques we already use,” said Pekosz.

If the CDC were to decide to divert vaccine production resources away from the seasonal flu vaccine completely to focus on a swine flu vaccine, it could create an even bigger problem.

“We know that seasonal flu is a result of a virus that transmits very easily in humans and is probably better matched to circulate in humans than swine N1H1,” Pekosz said. “If we chose to go with the swine component and it doesn’t come back next year we don’t have an effective vaccine.”

However, Compans said it is unlikely a seasonal vaccine would be abandoned completely for the year and it is more likely the swine flu vaccine effort would be combined into the seasonal flu vaccine effort.

If the H1N1 vaccine is developed in the coming months it “could be used in the near term to limit the spread” if the current outbreak is still ongoing said Compans, or alternately could be saved for distribution in next flu season.

“The flu season is typically coming to an end soon, so for that reason alone it may not spread very widely this year,” said Compans.

Because this swine flu outbreak occurred relatively late in the season a decision on a vaccine will have to be made soon if it is going to be ramped up in manufacturing, said Pekosz.

“When it comes to vaccine choice, it really is now a time game trying to understand how important this virus is going to be and making a decision sooner rather than later so we can prepare adequately for next years flu season.”

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