COVID-19 Vaccine trials ‘can’t detect’ virus risk reduction – Experts

PARIS – None of the trials of COVID-19 candidate vaccines can detect a reduction in serious outcomes such as hospitalization or death, a leading public health expert said Thursday.

Writing in the BMJ medical journal, associate editor Peter Doshi warned that not even phase 3 trials underway in the race for a vaccine can prove their product will prevent people contracting COVID-19. 

In a sobering essay, 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 percent. 

“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, ten of which are in the most advanced “phase 3” stage.

People sit as they wait their turn for vaccine trials at Abu Dhabi National Exhibition Center in Abu Dhabi, United Arab Emirates. The picture was taken on October 6, 2020. Khushnum Bhandari, Reuters

This is where a vaccine’s effectiveness is tested on a large scale, generally tens of thousands of people across several continents. 

But Doshi, assistant professor of pharmaceutical health services research at the University of Maryland School of Pharmacy, said that even the most advanced trials evaluate mild rather than severe disease. 

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

And few if any current trials are designed to determine whether there is a benefit among the elderly, a critical at-risk constituency. 

Without enrolling frail and elderly volunteers in trials in sufficient numbers, Doshi said, “there can be little basis for assuming any benefit against hospitalization 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 critical gaps in understanding how COVID-19 develops differently among individuals. 


Several trials have already been halted after participants became ill. 

Many countries prioritize vulnerable people once a vaccine is available, but Doshi said that those hoping for a miracle end to the pandemic would have to wait. 

He said that several pharmaceutical firms had designed their studies “to detect a relative risk reduction of at least 30 percent in participants developing laboratory confirmed COVID-19”. 

Recent studies have also confirmed that someone can be reinfected with COVID-19, a development that may impact how governments form their vaccination plans.

© Agence France-Presse

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