EMA's blood clot review exonerates AstraZeneca COVID-19 vaccine, but monitoring continues

The European Medicines Agency (EMA) on Thursday said a review by its Pharmacovigilance Risk Assessment Committee (PRAC) has determined that AstraZeneca's COVID-19 vaccine AZD1222 is safe and effective at preventing COVID-19, and that its benefits are "far greater" than any potential risks. According to the EMA, the investigation indicates that AZD1222 is not associated with an overall higher risk of thromboembolic events among vaccine recipients, although the agency could not conclusively rule out a link with very rare cases of blood clots associated with low platelet counts, so PRAC will continue to investigate. 

The review was undertaken following recent reports of blood clots in some people who have received at least one dose of the AstraZeneca vaccine in Europe, prompting multiple countries to suspend their rollout of the product as a precaution. However, shortly following the EMA's update, several reversed course, including Germany, Italy, France, the Netherlands and Portugal among others, and said they would resume vaccinations with AZD1222, while Sweden indicated that it would take "a few days" and decide next week.

The EMA said during its press briefing on Thursday that it found no batch or quality issues with the vaccine. The agency noted that as of March 16, around 20 million people in Europe had received AZD1222, which was authorised in the EU in late January and in the UK about a month earlier. It said there have been 469 reports of thromboembolic events following vaccination, both in studies prior to licensing and after rollout, with 191 of these spread out across Europe, not counting the UK and Switzerland. According to the regulator, this makes the incidence "lower than that expected in the general population."

Very rare cases of DIC, CVT in younger vaccinees

Among these instances of blood clot side-effects, the EMA said it reviewed seven reported cases of disseminated intravascular coagulation (DIC) and 18 cases of cerebral vein thrombosis (CVT), with nine resulting in deaths. The reported cases were almost all in women under the age of 55. According to the regulator, the incidence rates for these particular conditions were higher than what would have been expected statistically – echoing similar data from Germany's Paul Ehrlich Institute this week – although "a similar imbalance was not visible in the older population given the vaccine."

While there is not enough evidence at this point to draw a causal link, it is "possible and deserves further analysis," the EMA said, but it believes the benefits of AZD1222 still outweigh the "extremely small likelihood" of developing these conditions. PRAC will continue monitoring the situation, with additional laboratory data and real-world evidence expected to shed more light. It will also look at risks with other types of COVID-19 vaccines as well, although "no signal" has been identified so far. In the meantime, product information for AZD1222 will be updated to include more information on DIC and CVT risks.

EU bracing for third wave

The EMA's update coincided with a statement by the UK's Medicines and Healthcare products Regulatory Agency (MHRA), concluding that the "available evidence does not suggest that blood clots in veins are caused by [AZD1222]." However, it said a detailed review is underway of five possible UK cases of CVT co-occurring with lowered platelets soon after vaccination, out of about 11 million doses of the vaccine administered there to date.

Meanwhile, European Commission President Ursula von der Leyen warned that "the epidemiological situation is getting worse…We see the crest of a third wave forming in member states, and we know that we need to accelerate the vaccination rates." The EU has said it is aiming to inoculate 70% of its adult population by the end of the summer.

To read more Top Story articles, click here.

Reference Articles