Residents in the Wuqia County in the Kizilsu Kirgiz Autonomous Prefecture, Northwest China’s Xinjiang Uygur Autonomous Region, receive COVID-19 vaccine on June 5, 2021. Photo: VCG

Northwest China's Xinjiang Uygur Autonomous Region and Southwest China's Yunnan Province have launched a booster shot campaign for COVID-19 vaccines for local residents amid sporadic outbreaks of infections which saw a total of three new local asymptomatic cases registered on Friday. 

Xinjiang reported one local asymptomatic case in its capital Urumqi on Friday, a loader who works at a local logistics firm and hadn't visited a COVID-19-hit area or come into contact with any infected contacts, local government said on Friday evening. Origin-tracing work on the virus the worker was infected is in progress.

The booster shot campaign will focus on key groups, including those who work at ports, borders and key positions that ensure essential services remain uninterrupted, and those aged 60 or above, an official of the Xinjiang center for disease control and prevention (Xinjiang CDC) told media.

Xinjiang is using the same vaccines in booster campaign that was used across previous mass inoculations rollouts, the official told local media outlet Xinjiang Daily. 

In Xinjiang's latest round of virus outbreak since October 3, the region has found one confirmed case and five silent carriers of COVID-19 by Saturday morning. Among them, the confirmed case had been discharged from hospital after recovery, and two asymptomatic ones had been removed from isolation for medical observation, Xinjiang health authority said on Friday.

In Yunnan Province, the local government reported two asymptomatic cases in the border city Ruili on Friday. They were identified through nucleic acid tests conducted at the city's centralized isolation sites for close contacts.

Yunnan, which is home to 25 border cities and counties, also announced the initiation of a booster campaign. 

In Ruili, the inoculation campaign started on Thursday. Instead of focusing on key groups, Ruili provides the shot to all local adults who completed vaccination six months prior, China Central Television (CCTV) reported on Friday.

At least 18 provinces in the Chinese mainland reportedly have started booster shot programs among adults this week, in order to offer residents more protections against COVID-19 amid current sporadic emergence of infections.

A booster shot can definitely improve efficiency of the COVID-19 vaccine, said Shanghai-based vaccine expert Tao Lina. "[Current studies found that] the antibodies can increase by some 30 times after one gets a booster shot after completing vaccination for six months," Tao told the Global Times on Saturday.

Nonetheless, it remains to be seen how exactly long the effect of the booster shot will last, Tao added.