Nature Medicine | Spoonful of Medicine

Super-stretching the pandemic vaccine supply

The data are piling in, and it looks like one shot of H1N1 pandemic flu vaccine is enough to protect most healthy adults. And today, the FDA announced it has approved the vaccine.

That’s better news than expected—many experts had predicted two shots would be needed, putting pressure on tight supplies. But there clearly will still not be enough vaccine to go around, particularly in poor countries.

In the US, it is conceivable that high-risk populations like pregnant women might get vaccinated before the flu season hits full force, and most people could ultimately get the shot. That’s because the US has bought billions of dollars of vaccine—a price many countries cannot pay for such a limited commodity. Today the head of the World Health Organization, Margaret Chan, said she expected this “virus of extremes” to cause far more deaths in poor countries than in affluent ones.

The dosage in a single shot is 15 micrograms. But there is a way to bring down the dosage and further stretch the supply—using oil-in-water adjuvants, which have been approved for seasonal flu vaccines in Europe. Glaxo Smith Kline (GSK) recently showed that, with its AS03 adjuvant, a 5.25 microgram dose will protect 98 percent of adults (95 percent of the adults in its trials were protected with unadjuvanted vaccine at a 15 microgram dose). Stretching supplies further, GSK says it plans to sell shots with 3.75 microgram.

That’s a substantial reduction in dosage. But as I report in the latest issue of Nature Medicine, US regulatory authorities have not seemed eager to exercise their option to approve adjuvants in pandemic flu vaccine on an emergency basis—a decision that could have implications for global supply.

What do the recent data and vaccine approval mean for the prospects of using adjuvants in the US? I asked Amesh Adalja, a fellow at the Center for Biosecurity in Pittsburgh, Pennsylvania and a physician at the University of Pittsburgh Medical Center.

“I think the approval means that the pandemic vaccine will not be adjuvanted,” said Adalja.

Nonetheless, clinical trials are on deck at NIH to test adjuvanted vaccine. Adds Adalja: “I think that there is enough clamor about adjuvants that maybe we will see some trials using adjuvanted vaccine. The GSK adjuvant, AS03, can be mixed with some of the other manufacturers’ vaccines after production and we might get enough data for an approval (but probably too late for this flu season)."

You can access a great rundown of the new vaccine data by Adalja in his blog posting. Despite the new findings, he is skeptical about whether enough vaccine will be ready, even in affluent countries, by the time the peak of the pandemic is expected to hit.

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