Despite concerns about possible side-effects as Covid-19 vaccines are rolled out around the world, evidence from the UK’s well-advanced vaccination programme suggests recipients of the leading jabs have little to fear.
The UK Medicines and Healthcare products Regulatory Agency (MHRA) operates a Yellow Card surveillance scheme, which enables health professionals and members of the public to report suspected adverse events following vaccination.
By 14 February, the UK had administered 8.3m first doses of the BioNTech/Pfizer vaccine resulting in 26,823 cards and 6.9m first doses of the Oxford/AstraZeneca jab generating 31,427 cards.
For both vaccines, the “overwhelming majority” of adverse events were felt shortly after the injection and were not associated with “more serious or lasting illness”, the MHRA said. Those side effects included sore arms and generalised symptoms such as “flu-like” illness, headache, chills, fatigue, nausea, fever, dizziness, weakness, aching muscles, and rapid heartbeat, it said.
Severe allergic reactions — so-called anaphylaxis — were reported 168 times for the Pfizer vaccine and 105 times for the AstraZeneca product.
Overall, the data showed a slightly higher rate of adverse reaction for AstraZeneca’s adenovirus vaccine, approximately 0.45 per cent, than for Pfizer’s mRNA jab, approximately 0.3 per cent. But Dr June Raine, MHRA chief executive, warned against drawing conclusions from the Yellow Card reports about the relative safety of the shots.
“There are a range of factors that can lead to increased reporting of one vaccine over another — for instance socio-demographic factors of vaccine recipients or whether or not they have been encouraged by information, or a healthcare professional, to make a report,” she said.
The two vaccines have been used in different settings and the age distribution of people receiving the shots has differed too. During the first four weeks of the UK vaccination programme, when the oldest age group was targeted, only the Pfizer jab was available.
In general, younger adults tend to suffer more side-effects from vaccination than the elderly because their immune system responds more strongly to the vaccine.
Brendan Wren, a professor of vaccinology at the London School of Hygiene & Tropical Medicine, said he would not expect the AstraZeneca vaccine to produce more side-effects than the Pfizer shot in the same population.
“I can’t think of any scientific reason to suppose that using an adenovirus vector is any more likely to cause an adverse reaction than mRNA in a lipid nanoparticle, but lipid particles can occasionally have allergic complications,” he said.
Professor Beate Kampmann, director of The Vaccine Centre at the London School of Hygiene & Tropical Medicine, said: “There is nothing to be gained by digging for any subtle differences between the two products, as overall they are performing the same, and it’s great to see all of the granularity for this information to be publicly available.”
One pattern reported during the UK’s vaccination rollout has been a sudden feeling of cold starting within a day of the injection followed by a fever, often with sweating, headache, nausea and muscle aches. These effects often last for a day or two, like the flu-like illness reported during the vaccine’s clinical trials.
No deaths have been attributed directly to Covid-19 vaccination in the UK or elsewhere, though proving such a link would be extremely hard. Mortality statistics show that several thousand people would be expected to die of other causes within a week of the millions of jabs administered so far, according to the MHRA.
The MHRA has received about 400 reports of deaths shortly after vaccination, split evenly between the two vaccines. “Review of individual reports and patterns of reporting does not suggest the vaccine played a role in the death,” it said.