Trials ‘can’t detect’ risk reduction

None of the trials of Covid-19 candidate vaccines can detect a reduction in serious outcomes such as hospitalisation or death, a leading public health expert said yesterday.

Writing in the BMJ medical journal, associate editor Peter Doshi warned that not even phase 3 trials under way can prove their product will prevent people from contracting Covid-19.

In a sobering essay, Mr Doshi said those hoping for a breakthrough to end the pandemic would be disappointed, with some vaccines likely to reduce the risk of Covid-19 infection by only 30%.

“None of the trials currently under way are designed to detect a reduction in any serious outcome such as hospital admissions, use of intensive care, or deaths,” he wrote. “Nor are the vaccines being studied to determine whether they can interrupt transmission of the virus.”

The World Health Organization (WHO) has identified 42 candidate vaccines in clinical trials, 10 of which are in the most advanced “phase 3” stage. This is where a vaccine’s effectiveness is tested on a large scale, generally tens of thousands of people across several continents.

But Mr Doshi said even the most advanced trials are evaluating mild rather than severe disease.

This may be down to the numbers of people involved in trials, he said, pointing out that the majority of confirmed Covid-19 infections involve mild or no symptoms.

And few if any current trials are designed to find out whether there is a benefit among the elderly, a key atrisk constituency.

Without enrolling frail and elderly volunteers in trials in sufficient numbers, Doshi said “there can be little basis for assuming any benefit against hospitalisation or mortality.

He added that children, immunocompromised people and pregnant women had largely been excluded from trials, making it unlikely that the experiments will address key gaps in our understanding of how Covid-19 develops differently among individuals.

Several trials have already been halted after participants became ill.