Scientists hunt pandemic hotspots in race to test vaccines - Reuters

Scientists in Europe and the United States say the relative success of draconian lockdown and social distancing policies in some areas and countries means virus transmission rates may be at such low levels that there is not enough disease circulating to truly test potential vaccines.

But running large-scale clinical trials of potential vaccines against a completely new disease at speed is complex, scientists say.

Vaccine trials work by randomly dividing people into a treatment group and a control group, with the treatment group getting the experimental trial vaccine and the control group getting a placebo.

The hope is that infections within the control group will be higher, showing the trial vaccine is protecting the other group.

With COVID-19 epidemics in Britain, mainland Europe and the United States coming down from their peak and transmission rates of the coronavirus dropping, a key task for scientists is to chase fluctuating outbreaks and seek volunteers in sections of populations or in countries where the disease is still rife.

Among the first COVID-19 vaccines to move into phase two, or mid-stage, trials is one from the U.S.

He told Reuters that with COVID-19 disease transmission rates dropping in the UK there is a possibility that the trial would have to be halted if they didn’t have enough infections to yield a result.

Underscoring the level of concern in the industry, AstraZeneca’s chief executive Pascal Soriot said his researchers were even contemplating running so-called “challenge” trials - where participants would be given the experimental vaccine and then deliberately infected with COVID-19 to see if it worked.

Difficulty recruiting candidates for mid-stage vaccine trials in countries where the COVID-19 pandemic is on the wane may be foreshadowed by the experience of doctors seeking infected cases for the World Health Organization’s multi-country Solidarity trial of potential treatments for the disease - including the generic drug hydroxychloroquine and Gilead’s (GILD.O) remdesivir.