China is half way to reaching herd immunity against COVID-19, according to Shao Yiming, a researcher at the country's Center for Disease Control and Prevention.

China became the first country in the world to administer over 1 billion doses of COVID-19 vaccines by Saturday, thanks to the rapid roll-out of the vaccine.

The majority of the people vaccinated received shots developed by drug maker Sinopharm or Sinovac, both of which required two injections. 

"We had a plan to reach about half way to herd immunity in the first half of this year, and that's about 1 billion doses of the vaccines," Shao told CGTN on Tuesday via phone, adding that the goal was reached two weeks ahead of schedule.

Shao said China, with 1.4 billion people, has "the big task" to reach herd immunity for all of its population.

About 80 to 85 percent of the population needs to be vaccinated to achieve herd immunity, according to Shao. 

He said at least 1 billion Chinese are expected to be vaccinated by the end of the year.

China began the vaccine roll-out for essential groups in the second half of last year, and for the general population from February.

Health authorities said priority should be given to those in need of the first jab.

"Usually, the vaccine can provide enough protection within six months [after two doses]," Shao said. "We're collecting data and monitoring when people should have a booster dose." A booster dose is the additional jab to prompt prolonged protection.

He added that decisions will be data-driven and based on science.

China has offered more than 350 million doses of vaccines to other countries and regions as of the end of May, and pledged an initial 10 million doses to COVAX, the World Health Organization-led global vaccine initiative for developing countries.