A medical worker shows China's Sinovac Biotech Covid-19 vaccine at a public health center in Jakarta, on January 15, 2021. Photo: Aditya Irawan / NurPhoto via AFP

HONG KONG – While Western vaccine makers race to test the efficacy of their mRNA shots against the fast-spreading Omicron variant, bigger questions are swirling around China’s Sinovac, the world’s most widely distributed vaccine with 1.5 billion shots shipped.

Recent research shows that the Sinovac shot might not even be able to protect people from the disease’s original strains, much less the highly mutated Omicron, as most recipients’ antibody levels fell below the minimum required six months after a second injection.

Hong Kong health experts have recently said that those who received Sinovac, an inactivated rather than mRNA vaccine, could only be considered “fully vaccinated” after receiving a third shot.

Pfizer-BioNTech has acknowledged that its vaccine’s neutralizing antibody levels decreased against Omicron compared with the original strain of the virus and has recommended a booster shot to guard against the more contagious but possibly less severe variant.

Mainland China and Hong Kong, where most people have received Sinovac, will likely have to prolong their closed border measures including strict three-week quarantine rules to maintain their zero local infection goals in the face of Omicron, health experts said.

As of early December, 2.52 billion doses of vaccine have been administered on mainland China, which has a population of 1.4 billion. Most people have been inoculated with either Sinovac or the similarly locally-made Sinopharm, both of which have lower efficacy compared with Western-made shots, various studies show.

On October 21, China’s Ministry of Foreign Affairs said the country had provided more than 1.5 billion doses of its vaccines to more than 100 countries. It said for the full year of 2021 it would ship up to 2 billion doses overseas, including 100 million doses as donations.

As of Tuesday, about 9.54 million vaccine doses had been administered in Hong Kong, which has a population of 7.5 million. Around 4.78 million people have received at least one dose, accounting for 71% of the population aged 12 or above, the government says.

A student received a first dose of Sinovac in Denpasar, Bali. Photo: AFP

However, the government has not provided the breakdown of BioNTech and Sinovac recipients since November. At the end of October, about 37% of people received two doses of Sinovac while 63% were given BioNTech.

“It is necessary for people who received the Sinovac vaccine to get a third shot before they can be called fully vaccinated,” said David Hui, a professor of respiratory medicine at the Chinese University of Hong Kong. “Many places, including Singapore, have required their people to get a booster shot if they were given the Sinovac vaccine.”

On December 2, Singapore’s Ministry of Health said 70,000 people who received their second dose of Sinovac or Sinopharm vaccines were strongly encouraged to take a third dose before December 31 to maintain their fully vaccinated status from January 1.

According to research by the Chinese University of Hong Kong (CUHK)’s Faculty of Medicine, mRNA vaccines could help people generate several times more antibodies than inactivated vaccines.

Between March and August, 726 volunteers aged between 18 and 79 participated in CUHK research where about half were given Sinovac and the other half BioNTech. One month after injection, those with Sinovac had their neutralizing antibody levels at 69.45, compared with 251.6 of those who received BioNTech.

Six months after injection, only 16.3% of those with Sinovac had neutralizing antibodies above the minimum required level while 79.6% of those with BioNTech met the requirement.

“More and more evidence showed that all Sinovac recipients should get their third jab. But it’s a long road for Hong Kong to achieve this,” said Ho Pak-leung, head of the University of Hong Kong’s Center for Infection.

Ho said, in the long run, Hong Kong needed a high vaccination rate to resume quarantine-free travel for international travelers. He pointed out that many places had launched mandatory vaccination programs.

From November 11, Hong Kong’s immunocompromised patients and people with a higher risk of infection have been able to get a third Covid-19 vaccine dose free of charge. As of Thursday, only 8,798 have received a third dose.

High school students queue to receive the Sinovac vaccine in Nanjing in China’s eastern Jiangsu province. Photo: AFP

On mainland China, there is also no definite timetable for the resumption of quarantine-free international travel or border reopening with Hong Kong.

The low efficacy of inactivated vaccines leaves the country little to no room to choose to “live with the virus,” especially when the world is facing rising risks from the Omicron variant, which is said to be 4.2 times more contagious than the Delta variant.

On November 8, China’s Ministry of Science announced that Yunnan-based Walvax Biotechnology Co’s self-developed mRNA vaccine could undergo a phase-three clinical trial.

On November 27, Sinovac said it had been gathering information and samples overseas to evaluate how its inactivated vaccine would react to Omicron. It said it had also started developing vaccines that target Delta and Omicron.

Shanghai Fosun Pharmaceutical (Group), a Shanghai-listed company, said Tuesday it would actively work with its German partner BioNTech SE to develop a new vaccine targeting the Omicron strains.

It said it would likely take three to four months to gain regulatory approval. Pfizer-BioNTech also said on Wednesday that its first batches of the Omicron-based vaccine would be likely ready for delivery within 100 days, pending regulatory approval.

Last Saturday, Zhong Nanshan, a Chinese pulmonologist, said in a medical forum in Shenzhen that Omicron was less dangerous than expected while China’s vaccines had remained effective in fighting the pandemic.

Wu Zunyou, chief epidemiologist of the Chinese Center for Disease Control and Prevention, said on November 28 that China would continue its “zero local infection” policy by taking preventive measures such as mask-wearing, social-distancing and quarantine rules.

Currently, travelers entering mainland China must be isolated in designated hotels for 14 days while those entering Hong Kong from most countries are required to be quarantined for 21 days.

Hong Kong has taken the world’s most stringent quarantine standard as the government is seeking to reopen the border with the mainland, which may be open by the end of this month.

A nurse in China prepares to administer the Sinovac vaccine. As a new Covid variant is identified, the need for masks and jabs are not going to go away any time soon. Photo: AFP / George Calvelo / NurPhoto

Meanwhile, many countries that had previously used Sinovac or Sinopharm are quickly changing to use Western-made vaccines as they become more available. 

In July, Thailand and Indonesia announced that they would give their people one shot of Sinovac and another of Western vaccines. Thailand has basically stopped using the vaccine, despite the Chinese government’s sustained donations.

Malaysia has said people would get two BioNTech jabs after its 16 million Sinovac doses were used up.

Read: HK-China border reopening hangs on Omicron’s spread