That means vaccinated people might still be able to get infected and pass the virus on, although it would likely be at a much lower rate, said Deborah Fuller, a vaccine expert at the University of Washington. The warning came after two people reported severe reactions on the first day of vaccination.
Professor Stephen Powis, national medical director for the National Health Service in England, said health authorities were acting on a recommendation from the MHRA.
But it's unclear how well the vaccine works in people with HIV and other immune-system disorders.
An allergy is a medical condition that causes someone to become sick after eating, touching, or breathing something that is harmless to most people.
The Medicines and Healthcare products Regulatory Agency (MHRA) has given precautionary advice to NHS trusts that anyone who has a history of "significant" allergic reactions to medicines, food or vaccines should not receive the vaccine.
Hahn said the agency has already teed up the process to authorize the vaccine by filling out all the legal paperwork in advance, regardless of the ultimate decision. Several thousand people were vaccinated on Tuesday in hospital clinics on the first day of the United Kingdom rollout of the Covid jab. "Nothing that I see would delay an emergency-use authorization". In the meantime, they're telling people to skip the vaccine if they've had a history of serious allergic reactions.
"The trial has enrolled over 44,000 participants to date, over 42,000 of whom have received a second vaccination".
"As an illustration. even last evening we were looking at two case reports of allergic reactions", she said. The Pfizer data showed that about 0.6% of people had some form of allergic reaction in the trial on the vaccine.
Can I stop wearing a mask after getting a COVID-19 vaccine? The MHRA said the staff developed symptoms shortly after receiving the vaccine. The first Pfizer vaccines have already been administered in Britain and are expected to be approved and rolled out in the US soon.
Canada now has bought the most vaccines.
More serious side effects are reported to regulators or health officials for further investigation.
It was unclear if the announced results included only those taking part in the UAE trials or if they also included results from China and other countries.
Separately, the president of the Uniformed Firefighters Association told CNN this week that in an internal poll answered by 25 per cent of the workforce, 55 per cent of firefighters in the Fire Department of NY answered No to the question of whether they would take the vaccine if offered by their employer. It is similar to how polio vaccines are made. However, the Chinese government has approved the vaccine for emergency use.
The UK, home to about 67 million people, has ordered 40 million doses of the vaccine - enough to inoculate 20 million people, as it is given in two injections, 21 days apart.
Hai Do adapted this story for Learning English with reporting from the Associated Press and Reuters.
After the UAE vaccine announcement, city officials in Abu Dhabi said it would restart "all economic, tourism, cultural and entertainment activities in the emirate within two weeks". Susan Shand was the editor.