# 3477
One of the persistent rumors mentioned by flu reporters and bloggers for more than 2 months has been that the seed viruses being used to manufacture the swine flu vaccine aren’t growing particularly well in eggs.
Ten weeks ago, Maryn McKenna – writing for CIDRAP – in a piece entitled Path to swine flu vaccine has major hurdles, wrote:
Rumors are circulating among some flu scientists that the strain being used at the CDC for the vaccine seed strain is not growing well in eggs. The WHO and CDC appeared to acknowledge this Friday, disclosing that they are preparing two seed strains for manufacturers: one that was naturally reassorted by allowing viruses to mix in eggs, and another tuned via a patented process called reverse genetics that cuts and pastes genes from the swine virus with a non-pathogenic virus in order to achieve the highest possible growth rate. Manufacturers will be allowed to choose, the agencies said.
In my own article from early May, called A Vaccine Reality Check, I listed a number of possible obstacles to seeing large amounts of vaccine in the fall. One of them was:
The virus may not grow well in eggs (that happens sometimes), reducing the amount of antigen that can be produced.
Since then, there have been fleeting mentions by other reporters, and statements from the WHO regarding the need to incorporate dose-sparing (read: adjuvant) technology – which suggested yields might be suboptimal. But nothing definitive.
Tonight Helen Branswell of the Canadian Press brings us a long and informative article with news that the virus yield from egg based manufacturing has been 1/2 that normally seen with seasonal flu viruses.
Unless this problem can be overcome (they are working on it), the amount of antigen available to make vaccines this fall and winter is likely to be far below what was originally hoped for.
As always, Ms. Branswell does a terrific job bringing us the details. Follow the link to read the article in its entirety.
Swine flu vaccine production hits a snag: yield so far is 'less than optimal'
By Helen Branswell –
TORONTO — Swine flu vaccine production has hit a snag, with manufacturers reporting a disappointingly low yield when vaccines viruses are grown in eggs.
The World Health Organization says so far the yield for egg-based production is half or less what manufacturers get when they make vaccine to protect against seasonal H1N1 viruses. The lion's share of influenza vaccine is made by companies that grow the viruses in eggs.
New seed strains are being made in the hopes of increasing the vaccine yield, a report by the WHO's vaccine chief, Dr. Marie-Paule Kieny says.
But if the yield cannot be increased, it will slow the rate at which pandemic vaccine comes out of the production pipeline, adding to the time it takes to protect populations in countries like Canada that have purchased vaccine. And countries that haven't pre-ordered pandemic vaccine would face substantial delays before manufacturers have product to sell to them.
"There's nothing to suggest it will take longer to make vaccine, if in fact everything goes as planned. The question is: How much?" says Dr. Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
"There is nothing magical about making this virus. The questions will be: How much? When? and Where will it be available?"
The yield problem is revealed in presentations WHO staff made to last week's special meeting of the expert panel that advises the Geneva-based global health agency on vaccine issues.
