Q&A What do I need to know about the official guidance?
What are the potential side-effects from Covid vaccines?
All medications, including vaccines, have side-effects. The most common with the Covid jabs are mild and short-lived, including localised soreness, fatigue or aches and headaches.
However, the AstraZeneca vaccine has been linked to a small but concerning number of reports of blood clots combined with low platelet counts (platelets are cell fragments in our blood that help it to clot). These include a rare clot in the brain called cerebral venous sinus thrombosis (CVST). In an unvaccinated population, it is rare: upper estimates suggest there might be 15 to 16 such cases per million people per year. Also highly uncommon is a combination of CVST or other rare clots together with low platelets, and sometimes unusual antibodies – and that combination is at the centre of current concerns.
The Medicines and Healthcare products Regulatory Agency (MHRA) said recipients of the AstraZeneca jab should look out for new headaches, blurred vision, confusion or seizures that occur four days or more after vaccination.
While headaches are very common post-vaccine, Dr Josh Wright, the vice-president of the British Society for Haematology, stressed that those linked to CVST are unusually severe and persistent and progressively worsen over a period of days. The MHRA also flagged shortness of breath, chest pain, abdominal pain, leg swelling and unusual skin bruising as reasons to seek medical advice.
Once identified, the symptoms can be treated. Beverley Hunt, professor of thrombosis and haemostasis at King’s College London, said the first step would be to give a dose of concentrated antibodies which block the effect of the antibodies that could be causing the clotting.
How many cases have there been?
Up to and including 31 March, the MHRA said it had received 79 reports of blood clots combined with low platelets, including 19 deaths, following more than 20m doses of the AstraZeneca jab. That equates to about four cases for every million vaccinated individuals.
The MHRA said that 44 of the reports and 14 of the deaths related to CVST with a low platelet count. Of the 19 deaths, 11 were in people under the age of 50 and three were in people under 30.
Two cases of clots with a low platelet count have also been reported among recipients of the Pfizer/BioNTech jab. “This is a particularly rare and very unique
form of abnormal clotting,” said Wright. The European Medicines Agency (EMA) is also examining three cases of venous thromboembolism clots involving the Johnson & Johnson jab.
The MHRA says blood clots combined with low platelets can occur in unvaccinated people, and in those who have caught Covid, and that while evidence of a link with the AstraZeneca vaccine has become stronger, more research is needed.
How might the vaccine cause these problems?
This is unclear. But experts have noticed a similarity to a clotting event seen among people given the blood-thinning drug heparin, whereby antibodies are generated that result in platelets becoming activated. “In very rare situations, [heparin] can actually cause this platelet activation problem and lead to blood clots in unusual places. So there are some similarities,” said Wright.
According to Hunt, one possibility is that the AstraZeneca vaccine might also trigger the production of antibodies that activates platelets, causing them to form clots. In the process, platelets are used up, resulting in a fall in the platelet count.
What is the current official recommendation?
The MHRA, along with the EMA and the World Health Organization (WHO), have all repeatedly said people should continue taking the AstraZeneca shot because its benefits in preventing Covid infection far outweigh any risks.
However, yesterday the MHRA acknowledged a possible link between the jab and clots, adding that careful consideration should be given to those who may be at higher risk of certain types of clots.
In addition, the UK’s Joint Committee on Vaccination and Immunisation (JCVI) said it was recommending that people aged 18-29 should be offered other Covid vaccines, if available, provided they are healthy and at low risk of Covid. There are about 10 million 18-to-29-year-olds in the UK.
“Although the chance of any person receiving the vaccine experiencing a blood clot with low platelets is extremely small, because the risk of severe Covid in the under-30s with no underlying illness is also small, JCVI feel as a precautionary measure it is appropriate for those in this age group to be offered an alternative Covid vaccine,” said Prof Anthony Harnden, deputy chair of the JCVI.
Pregnant women should ask their doctors about the AstraZeneca jab, as pregnancy can increase the risk of blood clots, the MHRA said.
Meanwhile, yesterday, the EMA said the clotting syndrome should be listed as a very rare side effect of the AstraZeneca jab after reviewing 62 cases of CVST and 24 cases of splanchnic vein thrombosis, largely from Europe and the UK, where 25m doses of the jab have been given. Of these cases, 18 were fatal.
“So far, most of the cases reported have occurred in women under 60 years of age within two weeks of vaccination,” the EMA said, although specific risk factors have not yet been confirmed.
According to the MHRA, 51 of the 79 clotting cases and 13 of the deaths were in women, although women were more likely to receive the AstraZeneca jab than men.
Does the contraceptive pill increase the risk of blood clots more than the AstraZeneca jab?
Combined hormonal contraceptives, which contain oestrogen, have been associated with an increased risk of clots, including CVST, deep vein thrombosis and pulmonary embolism. According to an EMA review, the risk of blood clots ranged from five to 12 cases per 10,000 women who take combined hormonal contraceptives for a year, compared with two cases each year per 10,000 women who do not. The pill “is probably the commonest cause of cerebral sinus thrombosis, so it is a very good comparison,” said Hunt. The faculty for sexual and reproductive health stressed the risk of blood clots from the pill was also low – much smaller than the risk of having a blood clot if they were pregnant.
Adam Finn, professor of paediatrics at the University of Bristol, said other risk-benefit comparisons could also be made. “We’ve seen data that the annual risk of dying in a car crash if you regularly travel in a car is about 1 in 20,000, with a lifetime risk of about 1 in 240,” he said.
Should you have a second dose of the AstraZeneca jab?
The vast majority of people who had a first dose, including under30s, should get their second dose, with some exceptions. “Anyone who experienced cerebral or other major blood clots occurring with low levels of platelets after their first vaccine dose of Covid19 Vaccine AstraZeneca should not have their second dose,” the MHRA said. “Anyone who did not have these side effects should come forward for their second dose.”
Could other Covid vaccines cause these clotting problems?
Harnden said that at present this was unclear. “Because we don’t know what the causal mechanism is yet, and although there is a strong possibility this is caused by the AstraZeneca [jab] – we are not 100% certain – we can’t really postulate [about] other [vaccine] types at the moment,” he said.
But the occurrence of only two cases of clots and low platelets among those who got the Pfizer jab suggests the problem is linked to the AstraZeneca vaccine, he said.
One possibility is that there is a link to the type of vaccine, with the EMA examining whether other jabs using similar technology pose any risk. The Johnson & Johnson vaccine also uses a modified virus – but whereas the AstraZeneca vaccine uses a chimp adenovirus, the Johnson & Johnson vaccine uses a human cold virus.
Dr Peter Arlett at the EMA said so far there had been three cases of venous thromboembolism blood clots involving the Johnson & Johnson jab. “This is under close scrutiny: the [committee] is looking at it carefully.”
When did reports of problems emerge and how did countries initially respond?
Norway and Denmark were the first to temporarily halt the AstraZeneca jab on 11 March. Austria, Bulgaria, Cyprus, Denmark, Estonia, France, Germany, Ireland, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Portugal, Slovenia, Spain and Sweden, along with non EU-members Iceland and Norway, subsequently either paused the vaccine or banned the use of particular batches.
Germany’s health ministry said that the incidence of the events in AstraZeneca recipients appeared three or four times higher than would be expected, with young women seeming to be over-represented.
Belgium’s health agency initially said it would keep using AstraZeneca, as to stop vaccinating people would be “irresponsible”. Yesterday, Belgium announced it would restrict the jab to over-55s.
What restrictions have countries placed on AstraZeneca’s use?
Most countries have already resumed AstraZeneca inoculations, although often with restrictions. But Denmark and Norway have prolonged their initial suspension until mid-April.
Countries that have resumed use without restrictions include Austria, Bulgaria, Cyprus, Iceland, Ireland, Latvia, Lithuania and Romania. Italy has said people who do not want AstraZeneca may have another vaccine later.
Countries that have imposed restrictions include Canada (limited to people aged 55 and over); Finland (65 and over); France (55 and over); the Netherlands (60 and over); and Sweden (65 and over).
Germany is offering the shot only to people aged 60 and over and in high-priority groups, with under-60s who have had a first shot recommended to get a different one, and Spain is giving it to only to those aged 55-65, plus essential workers over 65.