13 May 2009 by Debora MacKenzie

A VACCINE against the Mexican swine flu sweeping the world is likely to arrive too late for most people, vaccine officials told New Scientist between a flurry of high-level industry meetings this week.

The World Health Organization is now considering whether to advise the world’s vaccine makers to switch from ordinary flu vaccine to the Mexican H1N1. As New Scientist went to press, a pandemic was officially on the cards, but even if the WHO gives the go-ahead, vaccine will arrive too late for many.

Studies so far suggest that H1N1 has been only slightly more lethal than ordinary flu (see “Preparing for when swine flu returns”). But while regular seasonal flu hits the very elderly hardest, this virus affects the young (see chart). And there are fears that it could become worse in subsequent waves like previous pandemics. “We are starting experiments to see what changes make this virus more dangerous,” says Ab Osterhaus of Erasmus University in Rotterdam, the Netherlands.

Vaccine makers are left with a dilemma. “If we make ordinary vaccine and the pandemic comes instead, we will be blamed,” says Norbert Hehme, chair of the industry’s flu vaccine task force. “If we make pandemic vaccine and get ordinary flu, we will have a shortage of ordinary vaccine, so we will also be blamed.”

So the industry will not switch to H1N1 vaccine without WHO approval and the go-ahead from governments with vaccine contracts, says Bram Palache, chair of the European Vaccine Manufacturers (EVM) flu vaccine group. And even if that happens soon, there will be none before September because of the time needed to produce it.

First companies need “seed” virus containing two genes for antigens, or surface proteins, from H1N1 and the rest from a standard vaccine strain. That was expected this week from labs working with the WHO. “We were told Monday we won’t get it till the end of May. I don’t know why,” says Luc Hessel of the EVM.

It then takes three weeks to make enough seed to grow in eggs – or at one Czech plant, in cell culture. None of the modern cell-culture plants planned in response to bird flu have been built – they would have made it possible to produce much more vaccine. Last year, the Belgian firm Solvay cancelled one planned for the US, citing insufficient demand for ordinary flu vaccine. “Potential demand for pandemic vaccine cannot justify the investment,” Palache says.

“It only takes three days to grow the virus in eggs, but weeks for testing and formulating,” Hessel adds. That means no vaccine until September, and no real quantities until October. Then countries have to administer millions of doses, which take weeks to take effect. In 1918, the worst wave of the pandemic hit in September.