A nurse prepares a dose of COVID-19 vaccine at the health service center of the Xiameilin community in Futian District, Shenzhen, south China's Guangdong Province, Jan. 24, 2021.  (Xinhua/Mao Siqian)

A door knob at a hospital in Suzhou of East China's Jiangsu Province returned a positive result for COVID-19 when sampled for nucleic acid testing on Sunday, raising concerns over environment contamination by COVID-19 vaccines and infection risks among humans it might possibly cause.

Experts noted that it should be investigated whether the positive result was caused by exposure to the COVID-19 vaccine when such a situation occurs, so that an infection by the actual virus won't be overlooked.

However, the general public shouldn't panic if such situations occur because contamination of the environment by an inactivated COVID-19 vaccine solution cannot infect humans, experts said.

The Suzhou hospital is one of the city's designated vaccination sites, according to a list released by the Suzhou government on January 10. The reason for the positive test result on the doorknob has not yet been determined.

The positive result has led to the hospital being closed for track and tracing purposes, the local authority announced on Monday. The hospital staff all returned negative nucleic acid test results.

Notably, recent nucleic acid tests taken on the environment at vaccination sites across some provinces and cities in China also revealed that samples collected from tables, walls, corridors and doorknobs of vaccination sites tested positive for the novel coronavirus, according to an announcement on Sunday by China's national Center for Disease Control and Prevention (CDC).

The aerosol produced during the vaccination process or inactivated vaccine solution residue may result in positive nucleic acid tests at vaccination sites due to the contamination of objects at the sites as well as personal goods of medical staff or the recipients coming into contact with contaminated environments, China CDC said.

Experts told the Global Times that it is actually normal to detect positive results when performing environment testing at vaccination sites; as it is inevitable that, based on regular vaccination procedures, the vaccine solution may contaminate the surrounding environment when it is administered.

"For example, when you draw out the vaccine liquid and vent the syringe, some vaccine liquid will drip out, causing contamination on objects or the environment," Tao Lina, a Shanghai-based medical expert on vaccines, told the Global Times, adding that a similar situation also occurs when other vaccines are administered as well.

Experts stressed that it has to be investigated where the nucleic acid of the COVID-19 detected in the environment is really from, so that real infections aren't overlooked, as the country continues to fight COVID-19. 

"When a positive result is found, we need to conduct research and determine whether it is caused by a vaccine or a wild virus strain based on the comprehensive situation, so as to reduce difficulties or confusions in epidemic prevention," a Beijing-based immunologist, who requested anonymity, told the Global Times.

Tao said that gene sequencing would help distinguish the virus from popular strains.

However, the general public shouldn't worry about being infected by vaccine contamination, as the virus in the inactivated vaccine has lost its infectivity and pathogenicity, experts noted.

"The inactivated vaccine will retain some RNA segments of the virus, but won't necessarily be a complete one, leading to a positive result in testing. Its segments are not alive, so people don't have to be panic," the Beijing-based expert said.

The China CDC warned that attention and research on such cases is still required despite not any positive test results being recorded by aerosol inhalation in nose swabs tests yet.

In the guidance it issued for environment inspection in vaccination sites, the CDC advised strengthening prevention measures at vaccination sites and improving medical waste management as well.