A high vaccination rate against COVID-19 is the prerequisite for a gradual easing of international travel restriction, said epidemiologist Zhang Wenhong on Sunday.

"The R0 of Omicron is between 7 to 8, while the number of its subvariant BA.2 is 8, and this will bring risks to senior people," Zhang said at an online forum on COVID-19.

R0 is the basic reproductive number used in epidemiology to measure the transmission potential of a disease. The higher the number is, the easier patients with the disease can infect people around them.

China has already administered 3.22 billion doses of vaccines, with more than 649 million people having received their booster shots, according to the National Health Commission.

Specifically, 56 percent of people aged 60 to 69, 48 percent of those in their 70s, and 19.7 percent of people in their 80s have received their booster shots.

Another prerequisite for the opening up of borders is having sufficient medication that can prevent COVID-19 patients from developing severe symptoms, Zhang said.

He noted that despite relatively high vaccination rates and adequate stockpiles of medicine in the Western countries, many senior citizens have died after they were infected with the Omicron variant. 

"Although the mortality rate for a patient infected with Omicron is low, the total death numbers will rise because of the high transmission rate," he said.

Zhang added that there must also be sufficient medical resources to deal with a possible surge in COVID-19 cases, something that has taken place in other countries.

"The more we prepare, the closer we are to reaching the final stage of the battle against COVID-19," he added.