Seniors have been excluded from the initial stages of China's COVID-19 vaccination program for several reasons, including ongoing trials and the way the inoculations will be administered, experts said.

But the nationwide vaccination plan will eventually be expanded to cover both children and seniors, the National Health Commission announced on Wednesday.

The vaccination of seniors is scheduled for the second stage of the national plan and is dependent on government approval of mass inoculations and increased vaccine production, the commission said.

In recent months, public debate has focused on whether to vaccinate seniors against COVID-19, as they are considered more likely to develop critical symptoms if infected due to weaker immune systems and underlying diseases.

Currently, people aged 18 to 59 whose jobs may put them at higher risk of becoming infected are being prioritized for vaccination. They include cold-chain workers, customs officers and those involved in the transportation of vaccines.

Shao Ming, a researcher with the Chinese Center for Disease Control and Prevention, said there are no medical restrictions on those aged 60 and above receiving the vaccines.

"We conducted the same trials on seniors in both phase I and phase II clinical trials, just like those aged between 18 and 59," Shao said.

He said seniors showed fewer side affects in the trials compared with younger people, so there were no safety concerns about them being vaccinated.

"The problem is that we can't call on enough senior volunteers for the phase III trial as the epidemic on the Chinese mainland is well contained," he said. "We don't have that many older patients.

"So we carried out the phase III trial in other countries, such as Brazil and Egypt. However, it's still hard to recruit enough senior volunteers. Take Brazil, for example. The volunteers who joined the trial are on-the-job medical workers whose ages are all below 60."

An insufficient number of senior volunteers is not the only reason for the staggered program, as raising awareness about self-protection from COVID-19 and available vaccination services will take time.

"It's difficult to organize vaccinations of seniors," said Liang Xiaofeng, vice-chairman of the Chinese Preventive Medicine Association.

"One reason is the seniors may have physical problems to overcome to get out of their houses to get vaccinated. So it's necessary to consider whether to provide seniors with door-to-door vaccination services or help them to get to designated immunization venues."

If healthcare workers are sent to homes to vaccinate seniors, it could create staffing problems, Liang warned.

"It usually takes two or three medical staff members to conduct vaccinations, and it takes them about half an hour to observe the status of the vaccinated person. It will be time-consuming work," he said.

Liang said seniors' unwillingness to be vaccinated and misguided ideas about preventive medicine are other problems that have to be dealt with.

"Many seniors think they won't get infected with the novel coronavirus or even consider it just another type of flu, so persuading them to get vaccinated is also a challenge," he said.

Both health experts stressed that the vaccines would help prevent seniors infected with COVID-19 from becoming critically ill, but they were not a "silver bullet" to fend off the epidemic.

Shao said seniors and younger people still need to continue to follow disease prevention measures to protect themselves, even if they have been vaccinated.

By Wednesday, 15 million COVID-19 vaccinations had been administered nationwide.