Should we be alarmed by reports of clots after AstraZeneca vaccination?

A growing number of European countries have suspended use of AstraZeneca’s Covid-19 vaccine over safety concerns after several cases of blood clots, brain haemorrhages and low platelet counts in people who had received the inoculation, with a small number of deaths reported.

The World Health Organization and AstraZeneca have insisted the shot is safe, and that there is no link between the vaccine and reported blood clots while Europe's medicines watchdog said on Tuesday the benefits of the vaccine continue to outweigh the risks. The European Medicines Agency will release results of its investigation on Thursday afternoon. 

But some European countries are ambivalent, opting to halt inoculation drives under a “precautionary” move.

The vaccine was developed by AstraZeneca and the University of Oxford in Britain, where — apparently without any major problems — more than 11 million doses have been administered — more than any other country. The UK reported about 11 people who developed blood clots after getting a shot. None were proven to have been caused by the vaccine. 

Across the EU and UK there have been 15 events of deep-vein thrombosis and 22 events of pulmonary embolism among those who received the vaccine, AstraZeneca said of the reports it received as of March 8.

Is there a causal link between AstraZeneca vaccine and blood clots? 

Events following each other chronologically are not necessarily corollary in nature. 

An epidemiological study would have to be carried out to ascertain a causal link, Pharmacoepidemiology Professor Stephen at the London School of Hygiene and Tropical Medicine said. Others say this is a sign that adverse reaction monitoring is working, not that the adverse event was caused by the vaccine.

Medical experts told the Washington Post that health conditions that surface after a vaccination campaign are usually a coincidence.

The pharmaceutical company and international regulators say there is no evidence the shot is to blame.

AstraZeneca said it had carefully reviewed the data on 17 million people who received doses across Europe and found there were 37 cases of people who developed blood clots. 

It said there was “no evidence of an increased risk” of blood clots in any age group or gender in any country.

In fact, it said the incidence of clots is much lower than would be expected to occur naturally in a general population of this size and is similar to that of other licenced Covid-19 vaccines.

European Medicines Agency Executive Director Emer Cooke said there was no indication that the blood clot incidents, which he called "very rare" had been caused by the vaccine, but that experts were assessing that possibility.

"The benefits continue to outweigh the risks, but this is a serious concern and it does need serious and detailed scientific evaluation. This is what we are involved in at the moment," Cooke told a news conference.

A draft report commissioned by the European Medicines Agency collated data from countries including Germany, Italy, Spain and Denmark and showed that the incidence rate for coagulation disorders like thromboembolism and haemorrhages ranged from 307.68/100,000 people in a year to 651.17/100,000 people per year. 

"The crazy thing is that, even if the correlation between the vaccine and blood clots were proved, it would be a rate of 0.007 out of a thousand," Silvestro Scotti, a family doctor in Naples and head of the Italian Federation of General Practitioners, told Reuters.

The World Health Organization and the EU’s European Medicines Agency have also said that the data does not suggest the vaccine caused the clots and that people should continue to be immunised.

“Many thousands of people develop blood clots annually in the EU for different reasons,” the European Medicines Agency said. The incidence in vaccinated people “seems not to be higher than that seen in the general population.”

“Things that just happen by coincidence will, because it’s health-related, be assumed to be caused by the vaccine, but that is, in most instances, not the case,” Evans told the Washington Post.

Which countries have halted inoculation drives?

So far, a handful of cases of bleeding, blood clots and low platelet counts have arisen amid 45 million doses of various vaccines administered in the European Union and its near neighbours. 

Germany has reported seven such cases, of which three died, out of 1.6 million people who received AstraZeneca.

Denmark and Norway have reported isolated cases of bleeding, blood clots and a low platelet count after inoculations with the AstraZeneca vaccine.

Austria suspended a batch of the vaccine following the death of a 49-year-old nurse from "severe bleeding disorders" days after receiving it.

Bulgaria suspended the use of the vaccine as it investigated the death of a woman with several underlying conditions who recently received the jab.

Italy suspended the use of the AstraZeneca vaccine following the death of a man hours after he had received a jab.

Sweden halted vaccinations after the Swedish Medical Products Agency said it had recorded 10 cases of blood clots and one case of low levels of platelets among people who were given the AstraZeneca vaccine, but not in combination.

Countries that halted vaccine use without experiencing side effects themselves are Iceland, France, Indonesia, Ireland, Spain, Congo, Venezuela and Bulgaria. 

Thailand briefly stopped using the vaccine last week but switched course with Prime Minister Prayuth Chan-ocha and cabinet members vaccinated with first shots of AstraZeneca.

Don’t these moves slow down a long-awaited vaccination drive? 

Yes. 

The World Health Organization has urged immunisations to continue while other experts say it puts a dent in slowing down Covid-19. 

"It is most regrettable that countries have stopped vaccination on such 'precautionary' grounds: it risks doing real harm to the goal of vaccinating enough people to slow the spread of the virus, and to end the pandemic," Peter English, a retired British government consultant in communicable disease control, told Reuters.

The European Medicines Associations said that while the investigation is going on, “the benefits of the AstraZeneca vaccine in preventing Covid-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects.”

Dr Michael Head, a senior research fellow in global health at the University of Southampton in England, said there is no data yet to justify suspending the AstraZeneca vaccine and called the decision “baffling.”

“Halting a vaccine rollout during a pandemic has consequences,” Head said. “This results in delays in protecting people, and the potential for increased vaccine hesitancy, as a result of people who have seen the headlines and understandably become concerned,” Head added.

According to Evans, “If there is no shortage whatsoever of alternative vaccines, then an extreme precautionary approach as taken in Denmark may be justified; if however, this action stops some people getting the vaccine who are then vulnerable to Covid-19, then it is a mistaken use of precaution."