AstraZeneca COVID-19 vaccine shows promise with two shots in Pig trial

"These results look encouraging that administering two injections … boosts antibody responses that can neutralise the virus, but it is the response in humans that's important," said Bryan Charleston, Pirbright's director.

AZD1222 is already in human trials, and AstraZeneca says it hopes to have data on efficacy later this year.

Preliminary data from a trial in six monkeys found that some of the monkeys given a single shot developed antibodies against the virus within 14 days, and all developed protective antibodies within 28 days.

More than 100 potential vaccines are being developed around the world to try to control the pandemic, which has already killed hundreds of thousands of people.

Stephen Griffin, an associate professor at Leeds University who was not directly involved in this work, said it was "an encouraging advance" and showed that "a so-called 'prime-boost' strategy gives rise to far better responses" than a single dose.

"Whilst these studies will need to be repeated within human subjects…this is a heartening study," he said.

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