Thailand to boost Sinovac with AstraZeneca as Delta variant drives worst COVID-19 outbreak

As Thailand faces its worst COVID-19 outbreak, authorities have been forced to change the country's vaccine regime and, in a world first, AstraZeneca will be used to boost immunity among people who have already been given the Sinovac shot. 

More than 10 million people are under strict restrictions and a curfew as infections of the Delta COVID-19 variant rise in the capital of Bangkok and surrounding provinces.

The Health Ministry has announced people who have received one dose of the Sinovac vaccine will now get the AstraZeneca shot as their second dose. 

And healthcare workers who have already received two Sinovac doses will get an AstraZeneca or Pfizer shot as a booster.

Thailand is recording nearly 9,000 new cases a day as well as 80 deaths a day — figures that have been steadily increasing for a month.

There have also been breakthrough infections in healthcare workers who have been fully vaccinated with two doses of Sinovac.

Officials in Thailand referenced a local study in their announcement, but experts say there is no peer-reviewed research on the approach.  

Infectious disease and vaccine expert Tony Cunningham from the Westmead Institute for Medical Research said Delta had "changed the whole scope of things". 

"It's a fairly desperate position for countries that are experiencing Delta surges and you just simply cannot rely on Sinovac alone," Professor Cunningham said.  

"But what they're doing is untested and untried."  

World Health Organization (WHO) chief scientist Soumya Swaminathan said the body was awaiting "data from mix and match studies of different vaccines" and warned individuals not to make decisions around mixing doses themselves. 

Sinovac is approved by the WHO and is one of the vaccines distributed under the COVAX facility. 

The Chinese-developed vaccine has an efficacy rate of 51 per cent, compared to AstraZeneca's 82 per cent.

Under WHO guidelines, vaccine manufacturers must hit a vaccine efficacy target of 50 per cent.  

But as epidemiologist Hassan Vally says, variants have reduced the effectiveness of all vaccines.  

"You've got a vaccine like Sinovac that's 51 per cent effective in the trials, which were testing against the original strain of SARS CoV-2, and now you've got these variants of concern," he said. 

"The immune response elicited by the vaccine is being evaded by these variants, so you're getting reduced effectiveness of these vaccines in the real world, which is why Thailand is seeing what it's seeing and why it's working less effectively against the Delta variant." 

Professor Cunningham said the perceived risk of AstraZeneca, and its links to a rare clotting disorder, had been magnified in Australia and many countries would love to have a ready supply of a vaccine that offered its level of protection.  

"In India, 91 per cent of people now want to get immunised. That's what proximity to this disease does to you." 

The bet COVAX made on supply from India 

Vaccines in Thailand are a hard to come by, particularly the AstraZeneca formulation. 

The country has administered about 12.57 million vaccine doses, with just over 13 per cent of the population receiving at least one dose.

Thailand does produce the AstraZeneca vaccine locally, but with a population of nearly 70 million, domestic supply is not enough to meet demand. 

On Thursday, AstraZeneca asked Thailand to extend the timeline for the delivery of 61 million doses of its COVID-19 vaccine by five months, a deputy minister said.

The move will likely put further pressure on the country's vaccine rollout. 

One of the largest manufacturers of the AstraZeneca vaccine is the Serum Institute in India, but the government there put a stop to vaccine exports when a second wave of COVID-19 hit the country earlier this year.

At the time, the WHO said India's vaccine export ban had affected 91 countries. 

Doses that had been earmarked for export across Asia and Africa, including orders promised under the COVAX facility, were diverted to the domestic population and exporting has not yet resumed.

India's second wave meant many countries did not receive their expected doses of the AstraZeneca vaccine. For those that used the Sinovac shot as a replacement, they are fighting the spread of variants with reduced protection.  

"We had to focus all the firepower and the vaccines on the Indian population because that was where it was needed the most," Serum Institute chief executive Adar Poonwalla told the India Global Forum earlier this month. 

"India will go back to supporting COVAX in a few months and start re-exporting vaccines so there is equitable distribution, which was the original objective of COVAX."  

On Monday, the organisation co-leading COVAX announced it had signed two advance purchase agreements with Sinopharm and Sinovac to provide up to 550 million vaccines to the program. 

Dr Vally said it was important to remember any protection was better than none. 

"If you have a choice between no vaccine and using Sinovac, well it's a reasonable vaccine given we are in a worldwide pandemic and any immunity is better than no immunity," he said. 

He said, if the evidence supported it, the Thailand strategy could be very useful.  

"If you have Sinovac, it's not the end of the story. There's then an opportunity to boost people's immunity," Dr Vally said. 

"All of us are probably going to be getting boosters of vaccines, whether you're in low-income or rich countries, for the next six years or longer because immunity is going to wane." 

Australia exporting AstraZeneca 

An initial delivery of Australian-made AstraZeneca vaccines has already been made to Timor-Leste, with the federal government flagging a total of 15 million doses will be supplied to Pacific neighbours by the middle of next year. 

But on current estimates, Australia could have tens of millions of excess doses of the locally made AstraZeneca vaccine. 

"We are going to be exporting our excess AstraZeneca … when Pfizer and Moderna come bursting in at the end of the year — that's my suspicion," Professor Cunningham said.  

Professor Cunningham added sharing AstraZeneca doses made in Australia with Asia Pacific neighbours was not just about being charitable: "It's going to stop new strains being generated in our vicinity."

Professor Cunningham said with new variants, came new vaccine supply challenges. 

"The most people we've ever immunised in the world is 90 million in 2009. We're now trying to immunise 6 billion. We've never done anything like that," he said.  

ABC/wires