GUANGZHOU, China — China has administered more than a billion doses of its Covid-19 vaccines, a key milestone in the world’s largest inoculation drive.

As of Saturday, 1,010,489,000 doses had been given to people in China, according to the country’s National Health Commission (NHC). More than 100 million doses had been administered in the six days up to and including Saturday.

It’s unclear how many people have been full inoculated as the government does not release those numbers. But Zhong Nanshan, one of China’s top health experts attached to the NHC, said in March that the country is aiming to have 40% of the population fully vaccinated by the end of June.

After the outbreak of the coronavirus in China last year, authorities moved to quickly bring it under control and largely succeeded in reopening the economy and returning life to normal. One reason behind the slow start to China’s vaccination drive earlier this year was that people did not see the urgency for getting inoculated.

But the campaign has since ramped up. It took China 25 days to climb from 100 million doses to 200 million doses — and just six days from 800 million to 900 million, according to state-run media Xinhua.

Still, new coronavirus outbreaks have happened in the country over the past year. Since late May, the major city of Guangzhou in the south of China has been battling the delta variant, which first emerged in India. It is the first time that variant has seen local transmission in mainland China.

The city reported zero new locally transmitted cases on Sunday following a mass testing drive and local lockdowns.

CNBC two visited vaccination sites in the city earlier this month and saw long lines as people rushed to get vaccinated.

The World Health Organization has approved for emergency use the Chinese-made Sinopharm since May, and Sinovac Covid-19 vaccines since June.

China has been shipping its vaccines to countries around the world including Brazil, the United Arab Emirates and Malaysia. However, U.S. and European health authorities have not authorized any Chinese vaccines for emergency use.

There have been questions over the effectiveness of the China-made vaccines. Efficacy rates for China’s Covid vaccines have been found to be lower than those developed by Pfizer-BioNTech and Moderna. 

Chile, another recipient of Chinese vaccines, released the results of a real-world study of over 10 million people in April. It found that the Sinovac vaccine reduces deaths by 80%. However, despite being one of the world’s most highly vaccinated countries, Chile saw cases surge in April.