Most countries which temporarily suspended the vaccine have now resumed administering shots following recommendations from the European Union's drug watchdog and the World Health Organisation (WHO).

"Among other things, it's about understanding if there is a mechanical explanation as to whether this is caused by the vaccine and also if there are specific groups that one can rule out", she said.

"We have today made a decision to extend our pause for another three weeks (until April 18th)", director of the Danish Health Authority Søren Brostrøm told a press conference.

Earlier Wednesday, Dr. Anthony Fauci, the top USA infectious disease expert, told reporters he hoped that when all the data was publicly vetted by federal regulators, it would dispel any hesitancy caused by the spat.

"The vaccine is very useful for the elderly as many become seriously ill with COVID-19 every day", the Swedish agency's director, Johan Carlson, said in a statement.

Sweden is now in the second phase of its vaccination programme, meaning the vaccine is offered to people aged over 65 (the oldest first), people in certain risk groups including transplant recipients, and healthcare staff working in close contact with people in these categories.

A patient gets the AstraZeneca vaccine on Wednesday in London.

The death of a second person in Denmark who died after getting the AstraZeneca vaccine was reported.

The guidance notes that the benefits of the vaccine outweigh the "very rare" risk of potential blood clots with low blood platelets after a patient has received it. On Thursday, Denmark announced it would continue its suspension of the vaccine.

AstraZeneca's newest effectiveness calculations were based on 190 COVID-19 cases that occurred during the US study, 49 more than it had included earlier in the week.

Some European authorities have questioned how protective the vaccine is in older adults. In the US study, it was 85% effective in volunteers 65 and older, the company said. He said the company looks forward to "the rollout of millions of doses across America". The latest analysis is based on 190 cases of COVID-19 among the more than 32,000 volunteers in the study. AstraZeneca cautioned that 14 additional possible cases already are being examined, which could lead to further changes in the data. The FDA will publicly debate all the evidence with its outside advisers before making a decision.

He highlighted growing frustration within the British drugmaker, which is forgoing profits from its vaccine in contrast with rivals such as Pfizer and its German partner, BioNTech.

Health officials in neighbouring Finland said late Wednesday that the country would resume using the AstraZeneca vaccine on Monday after a pause of over a week, but only would administer it to people over 65.