Closing in: a worker at Ethiopia's National Polio Laboratory in Addis Ababa. Credit: WHO

With the fight against polio close to being won, the newly appointed director-general of the World Health Organization (WHO), Lee Jong-wook, announced on 29 July that eradication of the disease by 2005 is one of his top priorities. But he said that more funds are needed to do the job properly.

Health workers agree that a final big push is needed. Poliovirus samples remain unmonitored in non-secure freezers across the world, and some vaccination programmes are lax. Any complacency threatens to undo years of gains, they say.

The WHO's US$3-billion Global Polio Eradication Initiative, launched in 1988, has been highly successful, slashing the number of polio cases from 350,000 in 125 countries to just 235 in seven countries this year.

“But there is a false sense of security that the end is in sight,” says David Heymann, the official appointed by Lee to lead the new push. The virus must be eliminated in the few countries where it remains, warns Heymann, as even a single case could spawn an outbreak that could be exported.

Lee has launched a three-month mass vaccination campaign, involving 175 million children in India, Nigeria, Pakistan and Egypt, to eliminate polio transmission by the end of 2004. But before polio can be declared the second disease to be eradicated (after smallpox in the 1970s), sources of potential new outbreaks must be contained.

A major source might be the widely used oral polio vaccine, an attenuated live virus that can mutate back to wild, virulent poliovirus in unvaccinated populations and cause outbreaks (see Nature 409, 278–280; 2001).

“If this happens often we could be in trouble,” admits Heymann. An alternative is the injectable Salk inactivated polio vaccine, which cannot cause disease. But this is hard to use efficiently in developing countries.

Poliovirus stocks held in laboratories across the world present another potential source of outbreaks. To stop this, the WHO this month launched a “Global action plan for laboratory containment of wild polioviruses”, akin to the 1970s programme that targeted smallpox stocks. This requires countries to search for stocks and either destroy them or, if they are needed to provide live virus for vaccine manufacture, store them in biosecure facilities.

There are also other potential sources of infection. Diagnostic stool samples from polio patients contain live poliovirus and are widely stored, “possibly in their thousands”, says Heymann. The WHO has responded by launching a stool inventory. Poliovirus contamination of laboratory cultures of other viruses has also been reported (M. Davies et al. Lancet 361, 1187–1188; 2003).