More than 18 million Shanghai residents, or 81.9 percent of the city's adults, have completed vaccination against COVID-19, local authorities said Thursday.

As of Wednesday, Shanghai had administered 36.89 million doses of COVID-19 vaccines to about 19.96 million residents, or 90.3 percent of the city's adult population, the city government said at a press conference, adding that an immunity defense is forming in the eastern metropolis.

Shanghai began a large-scale inoculation drive on March 1. The widely used inactivated vaccines require two shots to complete.

Over 1.4 billion doses of COVID-19 vaccines have been administered in China as of Tuesday, as the country continues to ramp up its inoculation drive, the National Health Commission said Wednesday.