AstraZeneca backs its COVID-19 shot as nations battle new surges

AstraZeneca has said it is standing by its coronavirus vaccine after a U.S. agency raised concerns about trial results that showed the shot to be highly effective in preventing COVID-19.

As immunization programs gather pace around the world, another vaccine ran into trouble on March 24 when Hong Kong and Macau suspended the Pfizer-BioNTech jab over what authorities said were packaging problems.

The uncertainties are a blow to scientists' hopes for a quick rollout of what they say is the best hope of ending a pandemic that has killed more than 2.7 million people.

AstraZeneca had published results from its U.S. trials on March 22, showing the vaccine to be 79 percent effective in preventing COVID-19, but the U.S. National Institute for Allergies and Infectious Diseases raised concerns that the results were outdated.

The firm backed its shot on March 23, saying a review found the interim results it had announced were "consistent", and that it would release new analysis and data "within 48 hours".

The AstraZeneca shot had been hailed as a potential game-changer in the fight against the pandemic, as it is cheaper and easier to store and transport than many of its rivals.

But public confidence in the drug has tumbled after more than a dozen countries temporarily suspended its rollout because of isolated cases of blood clots - even though the World Health Organization and regulators have found no link with the shot.

AstraZeneca has also struggled for months with production and supply chains, delivering only 30 percent of the doses it promised the European Union for the first quarter and sparking fury in Brussels.

The European Commission on March 24 will revise trade rules to strengthen its hand when it comes to...