Sinopharm vaccine 79% effective against Covid-19 – but what does this mean?

Vaccine was approved for use in the UAE this month after trials indicated it was 86 per cent effective

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The latest studies of the Covid-19 vaccine being rolled out across the UAE suggest it may offer less protection than originally claimed.

On Wednesday, Chinese state-owned Sinopharm said Phase-3 trials of the vaccine found it was 79 per cent effective against Covid-19, lower than rival drugs developed by Pfizer-BioNTech and Moderna.

“Sinopharm CNBG Beijing’s inactivated coronavirus vaccine exhibits safety after vaccination ... the protective effect of the vaccine against Covid-19 is 79.34 per cent,” said Beijing Institute of Biological Products, a Sinopharm subsidiary.

But how significant is this apparent setback?

What are the new findings?

The Sinopharm vaccine was approved for use in the UAE this month, following results from trials indicating it is 86 per cent effective in preventing Covid-19. Now updated findings from the trials suggest the vaccine is somewhat less effective, offering 79 per cent efficacy.

Coronavirus: UAE approves China's Sinopharm vaccine for use

Coronavirus: UAE approves China's Sinopharm vaccine for use

What is the reason for the lower efficacy?

As with the 86 per cent efficacy figure, no detailed figures have been released. Sinopharm declined to comment further, though a spokeswoman for an affiliate of the company said more information would be released at a later date.

It is not the first time there have been conflicting reports of vaccine efficacy.

AstraZeneca, which makes the vaccine approved by UK regulators, reported 62 per cent efficacy in one trial, but found 90 per cent efficacy in a smaller trial involving a lower dose, for reasons as yet unclear.

Last week, the health ministry of Turkey, which has ordered more than four million doses of a vaccine made by Chinese pharma company Sinovac, said its studies suggested 91 per cent efficacy. Meanwhile, researchers in Brazil simply stated their studies of the same vaccine had found an efficacy of “over 50 per cent”. Officials stated Sinovac asked them to delay releasing precise information until the company completes its analysis of trials in other countries.

Are the concerns justified?

The differing efficacy figures have prompted calls for more transparency by both Sinopharm and Sinovac. It is possible, however, that the varying figures simply reflect the inevitable uncertainty that surrounds the results of any clinical trial.

Testing vaccines involves recruiting thousands of volunteers and comparing how many of those who receive the vaccine develop Covid-19, relative to those injected with an ineffective “control” substance such as saline.

For example, if 10 out of 5,000 vaccinated people develop Covid-19 compared with 50 out of 5,000 unvaccinated people, the efficacy is said to be 80 per cent. But because of the relatively small numbers involved, this “headline” figure still carries a level of uncertainty. Statistical analysis shows that for such a trial the true efficacy can only reasonably be said to lie in the range of 60 and 90 per cent.

This is compounded by the fact that most of the vaccine trials are still ongoing. The final results may show additional people given the vaccine develop Covid-19, reducing the ultimate efficacy.

The uncertainty about the true efficacy shrinks as more results are included. Seen in this light, requests for extra time to pull together results from all the studies seem more reasonable.

What level of efficacy is worthwhile?

The World Health Organisation has stated that vaccines should ideally achieve at least 70 per cent efficacy, with 50 per cent being the minimum acceptable. So far, all the approved Covid-19 vaccines have achieved “headline figure” efficacy, meeting the WHO’s preferred standard. But until they are given to millions of people, the true efficacy will remain imprecise.

Their effectiveness in protecting against Covid-19 is only part of the story, in any case. There is mounting concern about whether vaccinated people can still spread the virus to others, despite remaining disease-free themselves.

This casts doubt over the growing belief that mass vaccinations will allow the world to return to “business as usual”, dispensing with measures such as social distancing and face masks.

“I think we need to assume that people who have been vaccinated also need to take the same precautions,” WHO chief scientist Dr Soumya Swaminathan said this month.

Robert Matthews is visiting professor of science at Aston University, Birmingham, UK