The hotly anticipated University of Oxford vaccine faces knock-on delays with its trials.
A month-long pause in the jab's development could mean volunteers who had already been given one shot may not be able to get the planned second.
The delay is due to American regulators investigating potential side effects, the Times reports.
A previous delay on September 6 was triggered by AstraZenaca, which is developing the vaccine with Oxford, after a trial participant in the UK fell ill.
Other people who had received the first shot were due for a second one next week, which has now been cancelled.
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They are now unsure if they will ever get the booster, Stat News reported.
“Now, we’re waiting as the lab rats in the corner,” one participant told the publication.
It is not known how many participants of the 30,000 strong trial were affected, or how much of an impact this will have in determining whether the vaccine is safe.
At the end of last week scientists working on the Oxford vaccine expressed hope that regulators could approve it before the beginning of 2021, The Times reported.
The European Medicines Agency (EMA) said last Thursday it has started reviewing data on AstraZeneca and Oxford University's potential vaccine, in real time, the first of such moves aimed at speeding up any approval process in the region for a vaccine.
The Times report added that plans under consideration by government include allowing a much wider group of healthcare staff to administer the vaccine, setting up of drive-through vaccination centres and recruiting help of armed forces.
