BEIJING - A commission under the World Health Organization (WHO) announced in Beijing on Thursday that China has retained its polio-free status, after successfully combating a severe outbreak in 2011.

After more than 10 years of being labeled as a "polio-free" country,China confirmed four cases of wild poliovirus infection in Xinjiang Uygur autonomous region on August 25, 2011.

Upon request, WHO labs later found the poliovirus was imported from neighboring Pakistan, where the disease remains endemic.

The Chinese government promptly launched emergency response plans and a massive vaccination campaign, according to a report issued Thursday at the closing session of the four-day 18th meeting of the WHO Regional Commission for the Certification of Poliomyelitis Eradication.

China's Ministry of Health confirmed that over 43 million people in Xinjiang had been vaccinated.

The last case was reported on October 9, 2011, taking the total count to 21, including two deaths, according to the ministry.

The commission said China had made an "exemplary response" by limiting the outbreak to 1.5 months from laboratory confirmation to onset of latest case and restricting it to four prefectures.

Outbreak investigation and response actions undertaken in China in 2011 serve as models for any other outbreak following importation globally, said the report.

The commission also announced that the Western Pacific Region is retaining its polio-free certification for being free of poliovirus for the past 12 months.

However, it warned that "the status is not a guarantee, shield or curtain," and called for global collaboration in eradicating polio.

Polio-free countries remain at risk until the disease has been eradicated globally, according to Dr Bruce Aylward, assistant director-general for polio, emergencies and country collaboration at the WHO.

Polio is a highly infectious disease that mainly affects children under five years of age. Infections sometimes lead to irreversible paralysis.

According to the WHO, only three countries - Afghanistan, Nigeria and Pakistan - remain polio-endemic, down from more than 125 in 1988.