Washington: A seven-week halt to a U.S. trial of the Covid vaccine developed by AstraZeneca Plc and the University of Oxford bumped it from pole position in the race for a protective shot, but it’s still in the leading pack.
High rates of infection as the pandemic regains strength and the large numbers of participants in other trials around the world should help keep the vaccine program on course, according to scientists.
The U.S. Food and Drug Administration authorized the trial to resume Friday, nearly two months after a volunteer in a U.K. study became ill, and weeks after other regulators elsewhere had cleared tests to resume. An initial diagnosis of the rare nerve disease transverse myelitis was ruled out and Oxford later said the person’s symptoms included limb weakness and were unlikely to be linked to the shot.
The swift resumption of the other trials will let health officials comb through more data as the American study proceeds. Soaring case numbers in Europe and the U.S. help because trial participants need to be exposed to enough of the virus to show a meaningful difference in infection rates between those receiving the shot and others who get a placebo.
“The AstraZeneca trial covers at least four countries and as cases of Covid-19 increase around the world this will shorten the time to attaining enough data to report back,” said Gordon Dougan, a professor at the University of Cambridge who has contributed to a number of key vaccines, including ones for cholera and typhoid. “I do not think the trial halts will cause too much of a delay in terms of timelines.”
Representatives for the FDA and Astra declined to comment on the impact of the delay. The company said Friday it was expecting results from late-stage trials this year, depending on infection rates. The shot produced a strong immune response in older adults in an earlier trial, the company said Monday, echoing previously reported findings in younger volunteers.
Other drugmakers are racing to produce a successful coronavirus vaccine by year-end, with a number of companies looking to submit data for approval soon. Pfizer Inc. said it could seek emergency-use authorization in the U.S. by late November for its vaccine with German partner BioNTech SE, while Moderna Inc. is also looking at the possibility of seeking emergency approval in 2020.
More than 20,000 volunteers have participated in the Astra-Oxford trials outside the U.S. in countries including the U.K., Brazil and South Africa, with a further 30,000 set to be tested in the American study. During the halt, operators of the U.S. trial were unable to recruit new volunteers.
The interruption may have created a break in the timeline for the vaccine’s two-dose regimen, according to Beate Kampmann, professor of pediatric infection and immunity at the London School of Hygiene & Tropical Medicine, but given the trial only started a week earlier the impact should be minimal.
“Of course the pause might have affected the interval to the second dose of vaccine,” which means some volunteers may not have been able to continue in the trial, said Kampmann. But “it is more important to complete these trials with the necessary due diligence than to rush the timeline for the sake of a few weeks.”
Regulators in Europe and the U.S. usually require at least 3,000 participants to have been profiled for safety with the dosage planned for use before authorizing a new vaccine, according to guidance.
Specific Covid-19 vaccine guidelines issued by the FDA in October said submissions for an emergency-use authorization should include a median of two months of follow-up data after a volunteer receives their last dose, well over 3,000 participants, and a minimum of five severe Covid infections in the placebo arm of the trial to show that the benefits of approving a shot quickly outweigh the risks.
While the FDA can approve medicines that haven’t been tested in the U.S., as long as the trials have been conducted in line with American standards, it’s not clear whether the agency would be prepared to approve a Covid-19 vaccine based only on data from other countries. With the Astra-Oxford vaccine already under an accelerated review in Europe, it’s possible the shot could be approved by European Union or U.K. regulators first.
“People have an impression that there’s the reluctance to use foreign data but it’s the quality of the data not where it comes from,” said Margaret Hamburg, FDA commissioner during the Obama administration. “One of the issues will be, what are the demographics of their European studies?”
U.S. officials have pushed vaccine developers to work to include a representative number of minorities in their clinical trials.
“The FDA will need to do a good job explaining its decisions around vaccines,” said Joshua Sharfstein, a professor at the Johns Hopkins Bloomberg School of Public Health and former FDA deputy commissioner. “That will include answering questions about the clinical studies used to guide regulatory decisions.”
–With assistance from Anna Edney. –Bloomberg
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