Nonetheless, the speed at which several countries have suspended use of the vaccine reflected a nervousness about its safety and effectiveness that contrasts sharply with the confidence that has been shown in other vaccines. Confidence in the vaccine has fallen in Germany, France, Italy, Spain and, to a lesser extent, Britain, according to polls.
Participants who received the vaccine in the trial had no increased risk of blood clots or related diseases. And specific research has found no cases of cerebral venous sinus thrombosis – blood clots in the brain that can lead to dangerous bleeding – which has raised some of the most serious concerns in Europe.
Michael Head, a senior researcher in global health at the University of Southampton in Britain, said the findings could allay concerns not only in Europe but also around the world. He said he had received messages in recent days from colleagues in Ghana worried about how to explain the fear of safety to people who had celebrated the arrival of the vaccine weeks earlier.
“Due to the slight aggression of the AstraZeneca vaccine over the past few weeks – and particularly over the past week or two in Europe – new data showing that it is safe and effective is, if you excuse the expression, a good dose of the arm, ”he says. “The publication of these results is actually quite timely, given the possible hesitation around the vaccine.”
The US trial also found no cases of serious neurological problems. This became a concern last summer after two AstraZeneca trial volunteers in Britain fell ill with neurological problems. Although these cases forced a seven-week shutdown in the US clinical study, the researchers ultimately concluded that the diseases could not be linked to the vaccine. Still, the delay has been a key factor in why AstraZeneca has fallen so far behind three other vaccine makers who have obtained emergency clearance in the United States.
The vaccine worked well in all ethnic and age groups, AstraZeneca said. The vaccine was 80% effective in about 6,000 people enrolled in trials over the age of 65 – findings that may allay concerns about insufficient clinical trial data on the vaccine’s effectiveness in the elderly. Some countries briefly limited vaccinations with the vaccine to younger people before reversing the course to allow its use in all age groups, after data from the vaccine’s rollout in Britain showed the vaccine offered strong protection for the elderly.
Even if the vaccine is not used in the United States, receiving emergency clearance from the FDA – whose rigorous review process is considered the global gold standard – would be an important step for AstraZeneca. Some countries that have yet to clear the vaccine may seek to follow the FDA’s lead.