GENEVA - Students across Europe may have their summer holidays extended, some Muslim nations are warning pregnant women not to attend the hajj and China is quarantining hundreds of foreign students.

It's all part of a global effort to slow the spread of swine flu until a vaccine becomes widely available - but experts and governments are divided on how well the measures will really work.

The World Health Organization said Tuesday that deaths from the new H1N1 virus have doubled in the past three weeks, rising to over 700 from about 330 at the start of July.

"We expect to see more cases and deaths in the future," WHO spokeswoman Aphaluck Bhatiasevi told The Associated Press in Geneva.

WHO gave no breakdown of the deaths, but as of last week, the United States reported 263 deaths, Canada had 45 deaths and Britain had 29. According to WHO's last update on July 6, Mexico reported 119 deaths.

Yet even Tuesday's figure of 700 deaths may seriously underestimate the true toll because not all swine flu cases are being picked up due to testing limitations.

The race is now on to develop and produce a vaccine that is effective against the global swine flu strain, but estimates for when such a jab will be available range from September to December.

In the meantime, the U.N. health agency is working with nations around the world to figure out what countries can do to tackle the expected explosion in cases later this year, when students and workers in the northern hemisphere return from summer vacation.

In a medical study released Tuesday, experts said school closures may be among the most effective measures to slow the spread of swine flu but warned of a considerable economic downside to the proposal.

Religious leaders, too, have been drawn into the debate after authorities in Jordan and health officials at a conference in Saudi Arabia recommended that people thought to be most at risk, including pregnant women and those with chronic diseases, refrain from performing the hajj pilgrimage to Saudi Arabia this year.

Arab health ministers are holding an emergency meeting Wednesday in Cairo to come up with a unified plan to confront the pandemic.

In New Zealand, the Roman Catholic Church banned priests from placing Communion wafers on the tongues of worshippers, while Chilean authorities suspended a northern religious celebration, prompting protests from the faithful.

"The key question is whether citizens will accept the measures governments impose," said Christian Drosten, head of the Institute for Virology at the University of Bonn, Germany.

"You need to get the population on board, otherwise your efforts won't work," he said. "Once people take the disease seriously, you'll begin to see the kind of social distancing that limits infection."

"But it's all a question of culture," Drosten added. "What works in Europe may not work in other countries, and vice versa."

China's practice of forcibly quarantining visitors has caused bewilderment elsewhere, particularly when foreign tourists have been sealed off in hotels for days on just the suspicion of infection.

In Britain, health officials' suggestion that women could put off planning to have children due to the global outbreak was met with ridicule - since the swine flu pandemic may last years.

One measure comes up again and again - school closures - but it has its own risks.

A paper published Tuesday in The Lancet Infectious Diseases medical journal argued that closing schools can help break the chain of transmission, slowing the pace of the disease, lessening the burden on health care systems and reducing the peak in worker absenteeism.

But the paper, written by researchers at London's Imperial College, also noted the considerable economic costs as parents are forced to stay home to look after their children.

France's Education Ministry has already prepared nearly 300 hours of educational programming for radio and television to allow those affected by school closures to follow their lessons, the Le Parisien daily reported.

The experience of school closures in the United States during the early days of the epidemic may prove to be the best guide.

Initially, authorities recommended that affected schools close for two weeks if there was a suspected case, but when the virus turned out to be milder than feared they switched to advising parents just to keep sick students home. Schools could still close a large number of students and staff were out sick.

"The best place for healthy kids is in school, where they can learn, where they can be educated, and where many of them get breakfast and lunch," Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention said last week.

Apart from school closures, WHO experts are also examining other measures including postponing mass gatherings such as sports events and concerts, Bhatiasevi said. That measure could be very unpopular worldwide, since national soccer leagues as well as U.S. football and Major League baseball all have heavy fall schedules.

In Switzerland, supermarket chains are even considering requiring customers to disinfect their hands and put on face masks as they enter the store.

"We can put these measures in place as quickly as we get food into the stores," said Urs Peter Naef, a spokesman for Migros, Switzerland's biggest chain.

Ultimately, the responsibility to decide what to do to keep the pandemic under control rests with individual governments, WHO spokeswoman Bhatiasevi said.

"Different countries could be facing a pandemic at different levels at different times," she said. "It is really up to countries to consider what mitigation efforts suit them."


Associated Press Writers Bradley S. Klapper in Geneva; Jenny Barchfield in Paris; Jamal Halaby in Amman, Jordan; Rebecca Santana in Cairo, Egypt; Eduardo Gallardo in Santiago, Chile; and AP Medical Writers Maria Cheng and Stephanie Nano contributed to this report.