However, while repeating that the vaccine’s benefits outweigh risks, it cautioned that people should be aware of the “remote possibility” of rare blood clots occurring, and must seek immediate medical attention in case of symptoms.
"A causal link with the vaccine is not proven, but is possible and further analysis is continuing," the European Medicines Agency (EMA) said in a statement.
EMA issued the statement after a hearing with a panel of independent external experts on Monday.
It spoke after several countries including Canada, Germany, France and Spain limited use of the drugmaker’s shot, after reports of a rare clotting condition following vaccination.
Frequently Asked Questions
A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.
There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.
Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.
Investigations by EMA and several national authorities in the EU continue, after initial probes deemed the vaccine safe for use following reports of a brain clotting ailment known as cerebral venous sinus thrombosis (CVST).
A high proportion among the reported cases affected young and middle-aged women but that did not lead EMA to conclude this cohort was particularly at risk from AstraZeneca’s shot.
Women were generally more prone to CVST than men and twice as many women as men had received AstraZeneca’s shot in the EU so far, said EMA’s head of safety monitoring, Peter Arlett.
“This is why at this stage it is difficult to disentangle why there has been a preponderance of reports of this very rare potential side effect in younger women in particular,” he added.
EMA had analysed 62 such cases globally, consulting also with regulators in India, Brazil and Britain, and 44 of the cases had occurred in the European Economic Area (EEA).
It had looked into 14 deaths, though not all were associated with CVST, said Arlett. About 9.2 million people in the EEA had received the shot by the assessment’s cut-off date of March 22.
Arlett did acknowledge the blood-clotting incidence rate was higher than what was normally expected in the young and middle-aged. Though he did not quantify the difference, he said it did not justify a change in recommendation.
“If we look into individuals under 60, we do see more cases of (CVST) than we would expect to see from the background rate,” said Arlett.
Germany vaccine oversight body PEI said on Tuesday it had registered 31 cases of CVST, which resulted in nine deaths, out of some 2.7 million people who have received the AstraZeneca vaccine.
EMA said a few of the German cases happened after its cut-off date and had not yet been included in its analysis.