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US flu vaccine trials may be effort wasted

The first human trials of a vaccine against H5N1 bird flu are likely to be a waste of time and money.

The formulations that the US plans to test are thought likely to be ineffective - and even if they do work it will take far too long to manufacture enough doses to prevent a pandemic strain wreaking havoc. Other countries are following more promising approaches, but they are not ready to start trials.

Fears that the H5N1 virus might mutate into a form capable of triggering a human pandemic have persuaded several countries to change strategy. Instead of waiting for a pandemic strain to emerge, health authorities are creating human vaccines against the current strain. Although these vaccines might not be perfect, the hope is that they will make the difference between life and death.

The sooner prototype vaccines are tested, the sooner vaccine makers can prepare to manufacture the vast quantities that might be needed. But so far the US is the only country to have ordered enough prototype vaccine to do clinical trials - and there are two major problems with its formulations.

No immunising effect

The key ingredient in any flu vaccine is the viral protein haemagglutinin, or HA. Vaccines against ordinary flu contain 15 micrograms each of three varieties of HA. The clinical trials planned by the US National Institute of Allergy and Infectious Diseases will test doses of 15 and 45 micrograms of H5 - the HA of the H5N1 virus killing people in Vietnam. The aim is to make the vaccine as similar to ordinary flu vaccines as possible, to ease approval by the FDA.

But several studies have shown that with HAs that people have not been exposed to before, such as H5, even doses higher than 15 micrograms have little or no immunising effect. "I predict they won't get much immune response at all," says Tony Colegate of the vaccine company Chiron in the UK, head of the industry's pandemic task force.

For this reason, other countries planning to test prototype vaccines - like Japan, Canada and Australia - will all add a chemical such as alum to boost the immune system reaction. This adjuvant is used in many childhood vaccines.

Another important benefit of adding an adjuvant is that far less HA will be needed in each dose. That is crucial because vaccine production capacity is limited.

Worldwide capacity

The single flu vaccine factory in the US would take six months to produce 180 million doses of 15 micrograms of H5, according to calculations by flu expert David Fedson in the latest issue of the Journal of Public Health Policy. And since past studies suggest people need two shots three weeks apart to develop immunity to novel strains, that is enough for only 90 million people. All vaccine plants worldwide could produce only enough for 450 million people.

In 2001, however, scientists in the UK found that with an adjuvant, two doses of just 7.5 micrograms of H5 were enough to induce immunity in previously unexposed people. And last year scientists at GlaxoSmithKline Biologicals found that two doses each of 1.9 micrograms of another novel HA were enough.

If a vaccine could be made with just 1.9 micrograms per dose, the world's vaccine plants could churn out 7.2 billion doses in six months, enough for 3.6 billion people, Fedson says. "That's probably more than the world's combined healthcare services can vaccinate."

Bruce Gellin, head of the US National Vaccine Programme Office, says the trials now being planned "are only the first in a long series". Last week his department asked for proposals to find ways to make vaccines stretch farther, he says. "We are taking this very seriously."

Journal reference: Journal of Public Health Policy



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