Britain’s two biggest drugs companies are also developing Covid-19 vaccines.
Potential jabs are being tested by FTSE 100 giants Astrazeneca and Glaxosmithkline.
Shares in Astra dipped 2 per cent after the Pfizer announcement. GSK was 2.1 per cent up. Pfizer shares jumped 7.7 per cent on Wall Street earlier in the day.
GSK boss Emma Walmsley has previously said she does not expect vaccines to become widely available to the public until at least the second half of 2020
Scientists say an effective vaccine is crucial for the world to return to normal life.
Astra’s potential jab, known formerly as AZD1222, has been developed jointly with scientists at Oxford University and is currently undergoing late-stage, mass trials.
Vaccines are typically made from weakened or harmless versions of a virus, which are then injected into the body to trigger an immune response.
This teaches a patient’s immune system how to create antibodies to fight that infection off in future.
However, the Oxford-Astra vaccine is different. It is made using technology that instead alters the genetic code of another virus found in chimps – also rendered harmless – to make it mimic the one that causes Covid-19 in humans.
This method has been in development for decades and was previously used to develop a potential vaccine for MERS, another type of coronavirus.
Astra is testing its jab on tens of thousands of volunteers globally and expects data on the its effectiveness within weeks.
If the results are positive, it says the jab could be approved by regulators and made available by the end of this year.
At the same time, GSK is involved with three potential vaccines being developed by Sanofi, Medicago and Clover Pharmaceuticals.
It has partnered with the firms to provide its adjuvant technology, which boosts the effectiveness of jabs.
This means smaller doses are needed per patient to trigger an immune response – and so supplies of a vaccines go further.
The Government has secured supplies of the potential vaccines from Astra and GSK as well as Pfizer. Residents and staff at care homes are likely to be first in line for the jabs. They will be followed by people aged over 80 and health workers.
GSK boss Emma Walmsley has previously said she does not expect vaccines to become widely available to the public until at least the second half of 2020 because of the logistical challenge any rollout poses.