Shanghai announced on Wednesday that 600,000 teenagers ages 12 to 17 will be allowed to take part in the country's free and voluntary COVID-19 vaccination program.

City authorities said that from Thursday young people ages 15 to 17 will be able to book vaccinations.

Since July, cities in Fujian, Jiangsu, Guangdong, Hubei and Heilongjiang provinces and the Guangxi Zhuang autonomous region have announced COVID-19 vaccination programs for minors above 12.

After implementing the program for 15 to 17-year-olds last month, some cities extended it to youngsters ages 12 to 14 this month.

"The world is still under heavy threat of the COVID-19 pandemic, and Shanghai faces constant risks and pressure to prevent the virus spreading from overseas," Sun Xiaodong, deputy director of the Shanghai Municipal Center for Disease Control and Prevention, told local newspaper Jiefang Daily.

"Vaccination as soon as possible is essential to enhancing personal and herd immunity among youths and for the entire society. It will effectively block the spread of the contagion."

While there has been a wave of outbreaks in a number of provincial-level regions since last month, Shanghai has only had one locally transmitted confirmed case. Tens of thousands of people related to the case have been tested for COVID-19 in the city and no other cases were detected.

"This has much to do with the fact that the vaccination rate among Shanghai residents above 18 has exceeded 85 percent," Sun said. "The domestically developed vaccines show strong efficacy in reducing the number of hospitalized and severe cases. Widespread vaccination makes the spread of the virus, including the mutated variants, less easy."

The Shanghai government said that parents of children ages 15 to 17 can make an appointment for vaccination through the Health Cloud app from Thursday. The teenagers must be accompanied by parents or guardians when they are inoculated, and will be vaccinated with either Sinopharm or Sinovac Biotech. The vaccination involves two shots, administered 14 to 56 days apart. Both vaccines have been approved for emergency use for young people ages 3 to 17.

The city government has not yet announced when 12 to 14-year-olds can book their vaccinations. Vaccination for expatriates and people from Hong Kong, Macao and Taiwan ages 12 to 17 may start at a later date, the authorities said.

The Shanghai Children's Medical Center said minors should follow the same guidelines as adults to determine whether they are suitable to receive a COVID-19 vaccination.

People who have uncontrolled epilepsy and other serious neurological diseases, have experienced severe allergic reactions to previous vaccinations, who have a fever or suffer from acute diseases, or who are undergoing an acute attack from a chronic disease are advised not to have the vaccine.

Patients receiving chemotherapy and radiotherapy before and after cancer surgery should not receive the vaccination.