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Two men wait outside a clinic after receiving the China-made Covid-19 Sinovac vaccine in Singapore. Photo: Getty Images

Covid-19: Singapore residents who took Sinovac turn to Pfizer to up their antibody counts, amid debate on booster shots

  • More than 85,000 people in the island nation have chosen to pay for Sinovac shots, despite having free access to Pfizer-BioNTech and Moderna jabs
  • Yet amid this sustained interest in Chinese vaccines, with Sinopharm now available, some are finding that they need a booster shot
Even after receiving her second dose of the Sinovac vaccine last month, Soh, a 43-year-old Singaporean, was unsure about her immunity levels. So she went to get an antibody test – and the result took her by surprise.

Her antibody count stood at 140, a figure her doctor said was about 10 times lower than what someone would have after two Pfizer-BioNTech doses, which along with Moderna shots are provided free to residents of the island nation above the age of 12.

“My doctor had repeatedly advised me to go for Pfizer or Moderna, but I decided to give Sinovac a try as I wanted to see how strong the vaccine is,” she said, adding that she had read reports of it being of lower efficacy than the others but did not believe that was the case.

“I was a little disappointed,” added Soh, who works in the banking industry and asked that only her last name be used for privacy reasons. She paid about S$20 (US$15) for the two jabs at a private clinic. Her husband and sister also received Sinovac doses, and their antibody counts were 400 and nine, respectively.

Following a sharp spike in Singapore’s domestic cases this month, and fearing they would catch Covid-19, all three of them decided to get another dose – but this time, they elected for Pfizer. Soh’s antibody count shot up to 1,900 after that jab.

Dr Leong Hoe Nam, an infectious diseases specialist at Rophi Clinic, one of 31 private clinics allowed to administer Sinovac jabs, said there had been an increasing number of patients who found there was inadequate protection from the Chinese-made vaccine.

“They took the Sinovac shots, did the blood test and saw low antibody levels, then opted for Pfizer as the third dose,” he said.

Even though antibody numbers do not necessarily correlate with the strength of an individual’s immunity, experts suggest they provide some indication of protection. Someone who has taken two Pfizer doses would typically have antibody levels of between 1,300 and 2,000 international units per millilitre, Leong said.

“But for Sinovac, it is zero to 40. We have a few with 200 to 300.”

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Kenneth Mak, the health ministry’s director of medical services, last month said Singapore residents who had taken the Sinovac vaccine or were inoculated with shots other than the ones offered in the city state could still participate in the national vaccination campaign.

“We have not stopped them, although data is still lacking [for the effectiveness of] using two different vaccines – we call this a heterologous vaccination strategy,” he said.

Globally, vaccination experts are continuing to weigh the value of a third dose, with countries such as Israel offering them amid a surge in cases. Other experts have raised moral questions, given that a shortage of vaccines in many parts of the world has left populations vulnerable to the proliferation of deadlier variants.

For Singapore, officials said they were looking at administering booster shots for those who are severely immuno-compromised, such as patients on cancer treatment.

In Hong Kong, which has struggled to boost its vaccination rates despite having ample supply – just over half of its 7.4 million people are fully vaccinated – the government last month said it would investigate and consider legal action against a 30-year-old Singaporean man who had two Pfizer jabs in the city despite having been fully vaccinated with Moderna in Singapore.

The man, who works in Hong Kong, apparently wanted a local vaccination record to go to bars, according to media reports. The government in a statement described his act as “dishonest” and condemned his “selfish and irresponsible act”.


Inside a plant in China producing the WHO-approved Sinovac Covid-19 vaccine

Inside a plant in China producing the WHO-approved Sinovac Covid-19 vaccine

Sustained interest

More than 85,000 people in Singapore have received two Sinovac vaccine doses since the first batch of 200,000 arrived in February this year. They are among the 80 per cent of Singapore’s 5.7 million people that have been fully vaccinated against Covid-19, as the country moves towards reopening its borders.

With about 9 per cent of Singapore’s population under the age of 12 and not currently eligible for vaccination, and some having received one jab, an estimated 460,000 have yet to receive a single dose. To keep boosting vaccination rates, the government has set up around 30 walk-in vaccination centres and deployed mobile vaccination units for elderly residents.

It has also made provisions for what seems to be sustained interest in Chinese vaccines. On August 10, with the initial shipment of Sinovac shots from February almost used up, the health ministry announced that more were expected to arrive in four to six weeks.

The tight supply had already prompted some to engage in black-market practices. Local media reported that people had auctioned their Sinovac appointments on mobile marketplace Carousell, offering them for S$50 to S$80.

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The posts were removed soon afterwards and the authorities issued a stern warning against exploiting individuals who wanted to be vaccinated, adding that this would be enforced.

On Monday, some private hospitals and clinics began administering the Sinopharm vaccine, which is also made in China, priced at between S$90 and S$100 for two doses, according to The Straits Times.

IHH Healthcare Singapore told the paper that more than 6,000 people had expressed interest in getting the Sinopharm vaccine while Raffles Medical Group said it had more than 10,000 registrations so far.

Raffles told This Week In Asia that it was preparing to administer the Sinopharm vaccine from September. StarMed Specialist Centre – which has administered 3,200 doses of Sinovac so far, but is no longer accepting new appointments as supplies deplete – is also expecting more stock of Sinopharm to arrive next month.

Dr Jeremy Lim, an associate professor at the National University of Singapore’s Saw Swee Hock School of Public Health, suggested reality was setting in for many that vaccinations were “pretty much essential” to reduce severe Covid-19.

“Hence, it’s really about which vaccine best fits one’s world views and concerns, no matter how justified or otherwise,” he said. “The clamour for the Chinese vaccines is thus understandable given the imperative for vaccination.”

Customers sit at socially distanced tables outside a restaurant in Singapore. Photo: Bloomberg

Booster shots

Sinovac reported 51 per cent efficacy against symptomatic Covid-19, according to the World Health Organization (WHO), while Sinopharm’s jab was 79 per cent effective. Pfizer-BioNTech and Moderna vaccines are assessed to have higher efficacy in clinical trials, at 95 per cent and 94 per cent, respectively.

The Singapore authorities did not previously tally those who had taken vaccines not offered in its national programme. The policy only changed earlier this month, with the health ministry saying it would recognise vaccines approved under the WHO’s emergency use listing, such as Sinovac, Sinopharm and AstraZeneca.

People vaccinated with those jabs would also benefit from differentiated measures such as being able to dine out and gather in bigger groups, it said, but would still be excluded from the country’s compensation scheme that covers serious side effects.

Following that announcement, clinics saw another surge in demand. “After an initial rush, interest gradually tapered off. We saw a spike again in interest when it was announced that recipients of Sinovac would be accorded the same vaccination status as those who received mRNA vaccines,” said Dr Louis Tan, CEO of the StarMed Specialist Centre, referring to the newer technology used in the Pfizer and Moderna vaccines. The likes of Sinovac use the traditional approach of an inactivated virus.

Many have cited this as one of the reasons they opted for the China-made jabs, including Teoh, 30, who works in the finance industry. “Admittedly, it was a personal apprehension over the usage of a new vaccine technology … moreover one that was approved rather rapidly,” he said.

A man leaves a subway station in the Chinatown district of Singapore. Photo: AFP

Dale Lim, a 28-year-old Singaporean, is also wary of the newer mRNA technology, characterising it as “relatively untested” compared with China’s “safer” vaccines. He was not given an option to have his antibody levels tested, but said he would consider taking another shot if his counts were low.

“In China, people are already taking their third jabs for increased antibodies so there’s that,” Lim said.

Tan from StarMed suggested that people with links to China were the primary group getting Sinovac shots. “They were either Chinese citizens working here or were Singaporeans with strong familial or business ties with China, and wanted to receive Sinovac in order to facilitate travel to China,” he said.

While Leong of the Rophi Clinic, which has administered more than 1,000 Sinovac shots, said results of the antibody tests largely served as further proof that the vaccine “isn’t very effective”, Dr Ling Li Min, another infectious diseases specialist, pointed out that antibody tests measured “just a single snapshot of a subset” of a complicated immune system.

Currently, there was no predetermined cut-off number to determine a good enough immune response, though she said a logical conjecture would be that “the higher the number, the better”.

There are other branches of the immune system that can help fight off infections that will not show in an antibody test, such as T cells, said Ashley St John, an immunologist at the Duke-NUS Medical School. This means that the presence of high levels of antibodies can be read as a sign of good protection but low counts might not necessarily indicate a lack of protection, she said.

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At StarMed, all tests on those who took the Sinovac vaccine so far came back positive for antibodies, according to Tan. The centre’s test does not show the level of the antibodies. But in one isolated case, a patient who received two doses of Sinovac vaccine abroad tested negative for antibodies, he said.

Lim of the Saw Swee Hock School of Public Health said there was limited guidance on booster shots at this time, and those concerned about waning immunity would therefore seek more doses.

Still, experts such as Teo Yik Ying, dean of the same public health institution, said he did not believe the use of less effective vaccines would weaken Singapore’s resilience against Covid-19 by too much.

Those would work in concert with the government-approved vaccines to protect Singapore’s population against severe illnesses arising from the disease, he said.

“The overall resilience against Covid-19 for a country is dependent on as many people coming forward to accept vaccines,” Teo said. “As long as the vaccines used are able to achieve this, then the country will still be able to achieve the long-term vision of living with endemic Covid-19.”

This article appeared in the South China Morning Post print edition as: Sinovac takers looking to Pfizer to up antibody count