As an encephalitis outbreak rages in northern India and Nepal, a vaccine in China could have been used to keep more than 360 children from dying and hundreds more from likely suffering a lifetime of mental and physical disabilities.
But borders and politics complicate the issue, making access impossible without money and a strong political will, researchers say.
The children are dying from Japanese encephalitis, found only in Asia. Though closely related to West Nile virus, this illness isn't as widely known as other mosquito-borne diseases such as malaria or dengue fever.
But it is the leading cause of viral encephalitis and neurological infection in Asia, typically attacking the poor and the young-- children aged between one and 15 who live near rice paddies in rural areas.
The outbreak in India's most populous state, Uttar Pradesh, began last month and has left more than 1,000 hospitalised, while more children die each day.
In Nepal, the disease has been spreading since April in the country's south, across the border from Uttar Pradesh.
Blinding headaches, seizures, nausea and high fever usually precede death, with the situation becoming so dire in India that doctors are using makeshift oxygen masks fashioned from cardboard cones and tubing on child victims after hospitals ran out of the real thing.
While drastically underreported, about 50,000 cases of Japanese encephalitis are recorded each year, including 15,000 deaths, according to the World Health Organisation.
Of the survivors, up to 75 percent suffer disabilities, including paralysis and mental retardation. The disease has no cure or effective treatment.
The Chinese vaccine, made from a weakened form of the virus, has been used widely within the communist country since 1988. Last year, about 200 deaths were reported nationwide, according to the Chinese Ministry of Health.
American Dr. Scott B. Halstead, research director at the Paediatric Dengue Vaccine Initiative, has seen firsthand how well it works.
He conducted a study in Nepal in 1999 that showed one injection of the Chinese vaccine was effective almost immediately with no side effects.
So far only South Korea, Nepal and Sri Lanka have licensed the Chinese vaccine, while others rely on limited supplies of another type of vaccine derived from mice brains. It is more expensive, causes more side effects, requires multiple doses and takes at least a month after the last dose to be effective, said Dr. Julie Jacobson, director of the Japanese Encephalitis Project at the US-based non-profit PATH.
The WHO in May adopted a 10-year global strategy to increase immunisations for different diseases worldwide, including Japanese encephalitis.
But the Chinese vaccine has not yet been added to its list of pre-qualified vaccines, which could be a deterrent for some countries waiting for the UN health agency's nod of approval.
It also keeps UN agencies in Asian countries from procuring the vaccine.
The WHO's Joachim Hombach in Geneva said he expects to see the Chinese vaccine or others now under development added to WHO's list in two to three years.
He said the Chinese manufacturer has not yet asked WHO to pre-qualify the vaccine, but it has recently been reviewed and WHO has published recommendations on it.
"If the product is not pre-qualified, it doesn't mean you cannot use it. It doesn't mean the product is bad," he said. "It just means we have not seen it."
He added that no encephalitis vaccines have been pre-qualified by the WHO, including the mouse brain vaccine used widely in the United States and Europe.
Halstead urged affected countries not to wait for the WHO's endorsement but to instead license the vaccine now and begin immunising children in high-risk areas.
"Let's say you're making an AIDS vaccine or TB-- they're all in the 'God I wish I could do it category, but I don't know how,'" he said.
"Here with Japanese encephalitis, you've got a vaccine that really works. There's no need to sputter or procrastinate."
Japanese encephalitis is spread mostly from pigs to people via mosquito. Annual outbreaks occur in Asia, often near rice paddies with water left over from monsoon rains. Like polio, only about 1 in 250 people infected ever develop symptoms, contributing to a high level of immunity among adults.
Japanese encephalitis is expanding, reaching northern Australia in the 1990s.
In India, Dr. O P Singh, Uttar Pradesh's director-general of health, said it would cost about Rs 2.5 billion to vaccinate more than 7 million children. The state's entire health budget is only Rs 1.06 billion.
On August 25, in Lucknow, a rickshaw driver's six-year-old son died in his father's arms, gasping for breath outside a government hospital. There were no beds and not enough doctors to help in the overcrowded facility.
"We can understand the anguish of a father. But what we can do?" said Dr. Anurag Yadav, a physician at the hospital.
"We do not have space to admit any more children."
It's stories like this that sadden Jacobson, who is working under a five-year, $27 million grant from the Bill & Melinda Gates Foundation to raise awareness about Japanese encephalitis and push for countries like India to license and administer the Chinese vaccine.
She said one hurdle is to convince leaders that the traditional spraying of houses with mosquito repellent and using bed nets do little to prevent this disease.
Unlike the mosquitoes that carry malaria and dengue fever, the species that carries Japanese encephalitis, also known as JE, typically bites people outside.
"The first JE patient that I saw just broke my heart," Jacobson said. "It's this little girl in this hospital lying there in this beautiful little pink dress and she had slipped into a coma, and there she was lying there in a pool of her own urine, completely unconscious while her family was there holding her hand."
(Associated Press writer Joy Banerjee contributed to this report from Lucknow, India)