The lower protection rates of China’s Covid-19 vaccines have raised concerns about shots being key to vaccinating Brazil to Indonesia, especially after its effectiveness was interviewed by one of the most senior Chinese health officials.
Bloomberg spoke to two experts about the vaccines, which the Sinovac Biotech Ltd. shot, which was the focus of a a crisis in confidence after achieving efficacy levels of just over 50% in a final stage in Brazil – the minimum level required by leading medicine regulators. Other Chinese vaccinations have yielded rates of 66% to 79%, which is still far behind the shots developed Pfizer Inc., Moderna Inc. and even the Russian Sputnik vaccine which recorded the protection figures of more than 90%.
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More than 30 countries have rolled out the Sinovac shot, most of them in the developing world, but also Hong Kong. The vaccine is the key to China’s own giant vaccination By the end of June, there are 560 million people – 40% of the population.
The good news is that the vaccines work very well to fight serious Covid infections. Fiona Russell of the Murdoch Children’s Research Institute in Melbourne and Paul Griffin, a professor at the University of Queensland in Brisbane. We asked them the most important questions about the merits of the Sinovac shot. Their comments have been edited and summarized for brief.
How effective is the Sinovac vaccine really?
Russell: The Sinovac study was to look at how the vaccine works against the whole range of clinical symptoms, from mild infections to serious ones, including death. The efficacy data of about 50% are for very mild diseases, which require no treatment. For infections requiring medical intervention it is about 84% and for moderate to severe Covid cases it is 100%.
This is what you expect from Covid vaccines – higher efficacy against more serious infections and lower against milder ones. From what I can see, it looks like a very rewarding vaccine. The problem with the data is that it does not include very old people or many people with co-morbidity.
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Griffin: My impression is that the efficacy is probably higher than the minimum threshold set by the World Health Organization, but less effective than a number of other leading vaccine candidates. Although it may be less effective against symptomatic Covid (mild infections), the effectiveness in severe cases is very high, which is an incredibly valuable property of any vaccine, including this one.
Why does it have different efficiency figures in different studies?
Russell: It caused a bit of confusion. The trials were conducted in Brazil, Indonesia and Turkey. Each of the studies yielded different results. In Brazil, you have the P.1 variant in circulation, and therefore the effectiveness of the vaccine may therefore differ. I do not know what spread in Turkey or Indonesia during the study, but it could of course change the results.
It is also very difficult to compare results from different trials directly, because they have to be interpreted in the context of the study design. The definitions of the case – the way in which a Covid-19 case is identified in a clinical trial – were different, and so were the endpoints of the studies.
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Griffin: It shows how variables in clinical trials can affect outcomes. Different strains circulating in a country are a major variable that can change the effectiveness. Virus strains are extremely important in determining the effectiveness of the vaccine.
What can be done to improve the vaccine?
Russell: The recommended schedule for two doses of Sinovac admission at trial was two weeks, although some people spread it longer than that, even one month apart. Theoretically, adjusting the schedule is definitely an option. Mixing vaccines – starting with one type and then amplifying with another – is another option, but there is much more we need to know about the variations.
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Griffin: It’s very likely that the dosing interval is critical and certainly sounds like it was also a variable in Sinovac’s clinical trials. We need another clinical trial to determine if the addition of another enhancer increases the effectiveness. As far as heterologous enhancement is concerned – using a mixture of different vaccines – research is underway. Many people are optimistic, but it’s hard to know until we have the data.
Is it possible to achieve herd immunity with Sinovac?
Russell: It depends on a number of things – the circulating variant, the coverage required and the extent to which the vaccine virus transmission occurs. But we do not yet have much data on the transfer.
Griffin: If we have a less effective vaccine, we will have to vaccinate more people to achieve it. The potential to reduce virus transmission is also likely to be less, but it is difficult to be sure without good data. With very high coverage, even a moderately effective vaccine is perhaps better than a very effective vaccine with poor coverage. It therefore depends on the survey among others.
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Should people take the Sinovac vaccine?
Russell: I will not hesitate, provided it ensures the approval of the regulatory authority. To protect people from ending up in hospitals, Sinovac’s shot looks great as the effectiveness data are 100% to prevent hospitalization and death.
Griffin: Yes. While this may mean that we do not reduce overall cases or achieve herd immunity, we will still succeed in reducing serious Covid infections and thus the burden on the healthcare system. If the vaccine is approved by the regulators concerned, I think we should trust that it is safe and effective in the population.
If there are several vaccines available, people may opt for one that is superior in clinical trials. But if this is not possible, it is better to have this vaccine than not to be vaccinated at all.
– With help by Michelle Fay Cortez and Dong Lyu