People under 40 will be offered an alternative to the Oxford/AstraZeneca vaccine where possible and while infection rates remain low, following a recommendation from government advisers.
It comes after the Joint Committee on Vaccination and Immunisation (JCVI) reviewed the speed and uptake of Covid vaccines in the UK and the latest figures on very rare blood clots after first shots of the AstraZeneca vaccine.
With the vaccination programme going well and case rates low, the chances of a major surge in hospitalisations and deaths have receded, leading advisers to believe a more precautionary approach can now be taken in 30- to 39-year-olds by offering the Pfizer/BioNTech or NIH/Moderna shots when available.
UK and European regulators have recorded a small number of people who have developed unusual blood clots with low platelets after receiving the AstraZeneca vaccine. Further cases have been reported in the US following the Johnson & Johnson jab, which is based on a similar technology.
The UK Medicines and Healthcare products Regulatory Agency (MHRA) has logged 242 cases of blood clots after 28.5m doses of the AstraZeneca shot, equivalent to about one case per 100,000 shots. The clots, 49 of which were fatal, occurred in people aged 18 to 93, including 141 women. Six cases have been reported after a second dose.
The rates appear to be slightly higher among younger people with 10.1 cases per million doses in 40- to 49-year-olds compared with 17.4 cases per million doses, or one in 60,000, among those aged 30 to 39.
Because coronavirus tends to cause far more severe disease and many more deaths in older people, the benefits of the vaccine easily outweigh the extremely low risk of blood clots. But the disease is usually far less serious in younger people, making the decision more finely balanced. Last month, the MHRA recommended under-30s be offered an alternative to the AstraZeneca vaccine because their risk of falling ill from the virus is so low.
The JCVI advises that where possible alternatives should now be offered to under-40s without underlying health conditions, as long as it does not cause any substantial delays to the vaccination programme.
Urging people to get vaccinated, the group warned that any slowdown in the speed or uptake of the vaccine would risk a more severe third wave of infection later this year.
Quick GuideCovid vaccine side-effects: what are they, who gets them and why?
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What are the most common side-effects from the Covid vaccines?
According to Public Health England, most side-effects from the Covid vaccines – Pfizer/BioNTech and Oxford/AstraZeneca – are mild and short-lived. These include soreness where the jab was given, feeling tired or achy and headaches. Uncommon side-effects include having swollen lymph nodes.
Why do the common side-effects occur?
“The sore arm can be either due to the trauma of the needle in the muscle, or local inflammation in the muscle probably because of the chemicals in the injection,” said Prof Robert Read, head of clinical and experimental sciences within medicine at the University of Southampton and director of the NIHR Southampton Biomedical Research Centre.
“The other common side-effects – the muscle aches, flu-like illness and fatigue – are probably due to generalised activation of the immune system caused by the vaccine. What this means is that the white blood cells that are stimulated by the vaccine to make antibodies themselves have to secrete chemicals called cytokines, interferons and chemokines, which function to send messages from cell to cell to become activated.”
Are blood clots a side-effect of the vaccines?
The Oxford/AstraZeneca jab 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). Distribution of the Johnson & Johnson vaccine has been "paused" in the US while scientists investigate six incidences of a rare type of blood clot.
These include a rare clot in the brain called cerebral venous sinus thrombosis (CVST). In an unvaccinated population, upper estimates suggest there may be 15 to 16 cases per million people per year.
The Medicines and Healthcare products Regulatory Agency (MHRA) said recipients of the Oxford/AstraZeneca jab should look out for new headaches, blurred vision, confusion or seizures that occur four days or more after vaccination. The MHRA also flagged shortness of breath, chest pain, abdominal pain, leg swelling and unusual skin bruising as reasons to seek medical advice.
Up to and including 31 March, the MHRA said it received 79 reports of cases of blood clots combined with low platelets, including 19 deaths, following more than 20m doses of the Oxford/AstraZeneca jab. That equates to about four cases for every million vaccinated individuals.
Two cases of blood clots with a low platelet count have also been reported among recipients of the Pfizer/BioNTech jab. The European Medicines Agency is also examining three cases of venous thromboembolism blood clots involving the Johnson & Johnson jab.
The MHRA says blood clots combined with low platelets can occur naturally in unvaccinated people as well as in those who have caught Covid, and that while evidence of a link with the Oxford/AstraZeneca vaccine has become stronger, more research is needed.
Nicola Davis Science correspondent
Prof Wei Shen Lim, the chair of the JCVI’s Covid-19 group, said safety remained the number one priority.
“We have continued to assess the benefit/risk balance of Covid-19 vaccines in light of UK infection rates and the latest information from the MHRA on the extremely rare event of blood clots and low platelet counts following vaccination,” he said.
“As Covid-19 rates continue to come under control, we are advising that adults aged 18 to 39 years with no underlying health conditions are offered an alternative to the Oxford/AstraZeneca vaccine, if available and if it does not cause delays in having the vaccine.”
Dr June Raine, the MHRA chief executive, said the regulator’s position remained that the benefits of the AstraZeneca vaccine against Covid-19 “continued to outweigh the risks for the vast majority of people”.
“The balance of benefits and risks is very favourable for older people but is more finely balanced for younger people and we advise that this evolving evidence should be taken into account when considering the use of the vaccine, as JVCI has done.”
A government spokesperson said: “The government will follow today’s updated advice, which sets out that, as a precaution, it is preferable for people under the age of 40 with no underlying health conditions to be offered an alternative vaccine where possible once they are eligible, and only if doing so does not cause a substantial delay in accessing a vaccination.
“More than 50m vaccines overall have already been administered, and our current vaccine supply and rate of infection means we are able to take this precautionary step while remaining on track to achieve our target of offering a vaccine to all adults by the end of July.”
According to Public Health England (PHE), the vaccine programme is estimated to have prevented more than 10,000 deaths in England alone by the end of March.