LONDON — Health experts say extraordinary measures against swine flu — most notably quarantines imposed by China, where entire planeloads of passengers were isolated if one traveler had symptoms — have failed to contain the disease.

Despite initially declaring success, Beijing now acknowledges its swine flu outbreak is much larger than official numbers show. China's official count of some 63,000 reported illnesses with 53 deaths dwarfs estimates of millions of cases with nearly 4,000 deaths in the United States, a nation with about a third of China's population.

Dr. Michael O'Leary, WHO's top representative in China, says there has been a dramatic spike in Chinese swine flu cases recently and those reported by the government are only "minimum numbers."

China's Health Minister Chen Zhu defended his country's aggressive quarantine policy, telling the AP on Wednesday that the measures helped slow the spread of the virus long enough for China to develop a vaccine, which authorities are now scrambling to administer.