PUSH AND PULL.(The Talk of the Town)

A couple of weeks ago, Gordon Brown, Britain's Chancellor of the Exchequer, made a promise. The United Kingdom, he said, would buy up to three hundred million doses of a new malaria vaccine for the developing world. It was a welcome sign that the West is finally paying attention to the most important problem in global public health; namely, the spread of infectious diseases like malaria, tuberculosis, and aids. It was also something else: a dramatic innovation in the way those diseases are fought.

That's because the vaccine that the U.K. promised to buy doesn't exist yet. There are several good candidates for a malaria vaccine, and one of them, being developed by GlaxoSmithKline, showed excellent results recently in a clinical trial in Mozambique, where it cut the risk of developing severe malaria by fifty-eight per cent. But there are still years of testing and hundreds of millions of dollars in development costs before any viable product could be sold. What Brown's announcement guarantees is that if an effective vaccine emerges there will be someone to buy it at a fair price.

Usually, a company that invents something useful doesn't have much trouble selling it. But vaccines--especially for diseases in the developing world--are notorious exceptions to this rule. To begin with, Third World countries have unimaginably tiny amounts to spend on public health. (The poorer African countries spend eighteen dollars per person a year on health. We spend five thousand dollars.) And then the market value of a vaccine may be a fraction of its social value. If you're vaccinated, it not only makes you safer; it makes me and my children safer, too. So though you might be willing to pay the vaccine-maker just two dollars for a shot, its value to your community might be twenty times as great. Governments, of course, could make up the difference, but, historically, they haven't been willing to. Instead, they've used their regulatory and bargaining powers to drive prices down to the bare minimum.

The result is that drug companies have put very little money into vaccine research. They'd much rather invest in an anti-arthritis drug that well-insured Americans will take every day than a vaccine that may never command a fair price. (Just a few years ago, a promising malaria-vaccine candidate that had been tested in Papua New Guinea was abandoned for lack of funding.) Meanwhile, diseases like malaria and tuberculosis have continued to ravage the Third World. Hundreds of millions of people are newly infected every year. And the burden of disease has helped keep sub-Saharan Africa poor: students who are in and out of school have a hard time learning, ailing workers aren't very productive, and Western firms are loath to invest in countries where such diseases are endemic.

When the private sector isn't providing the innovations we need, the traditional answer is to have the ...