Analysis: rare side-effects mean that confidence in both the Johnson & Johnson and Oxford/AstraZeneca vaccines is now shaken


A syringe is filled with the Johnson & Johnson vaccine
The US is investigating six cases of blood clotting, from 6.8m doses of the Johnson & Johnson vaccine. Photograph: Patrick T Fallon/AFP/Getty Images

The call in the US for a pause in the use of the single-shot Johnson & Johnson Covid vaccine is another blow to hopes of vaccinating the whole world as fast as possible.

Health agencies recommended that US states pause use of the jab while investigations take place into six cases of women who have experienced rare blood clotting events combined with low platelets in the days following vaccination.

J&J announced it would also “proactively delay the rollout of our vaccine in Europe”, where the European Medicines Agency was already reviewing the US reports.

The six cases in the US – from 6.8m doses of J&J vaccine administered – seem to be similar to those that have caused alarm across Europe, linked to the Oxford/AstraZeneca vaccine. Some countries have suspended the Oxford/AstraZeneca vaccine while others have imposed age limits. In France, it will not be given to anyone under 55, while in Germany it is offered to the over-60s. The UK is allowing the under-30s to choose an alternative.

Between them the AstraZeneca and J&J vaccines were the best chance for many developing countries. The Oxford/AstraZeneca vaccine is being produced at no profit and is easy to transport and store at room temperature. That was deliberate – the university and the company have pledged to make it highly accessible. The J&J vaccine is the other great hope, because it is given as one dose, not two, cutting the cost and making it easier for countries with shaky health systems to mass-vaccinate.

After the extensive probe into what is happening with the Oxford/AstraZeneca vaccine, none of the scientists are very surprised that similar cases involving blood clotting should come to light with J&J’s version.

The two vaccines – and also the Russian Sputnik vaccine – are designed in the same way. They use a common cold virus – from chimps in the Oxford/AstraZeneca vaccine and from humans in J&J’s – to deliver proteins from the coronavirus into the body which then trigger an immune response in the shape of antibodies and T-cells that will fight off the real thing.

It now looks as though this technology may have something to do with this rare condition, which the European Medicines Agency has listed as an official side-effect in the case of the Oxford/AstraZeneca vaccine. We have not yet heard whether there are cases linked to the Sputnik vaccine.

The blood clotting with low platelets stumped doctors at first. It looked like a condition triggered by the blood-thinning drug heparin – but none of the patients had been given it before they fell ill. In fact, most seem to have been healthy younger adults. But somehow, the vaccine may have triggered an immune system reaction, generating antibodies that have been responsible for clots developing in the brain and elsewhere in the body.

This is still rare. In the UK, which has more cases than any other country because it has given more shots of the Oxford/AstraZeneca vaccine, it is a four in a million occurrence. In the US so far, it is less than one in a million, but other cases may yet be picked up. Doctors can now recognise it and treat it, which will reduce the numbers who die – 19 out of 79 have died in the UK, but some of those before doctors knew what to do about it.

The existence of these cases will shake confidence in the Oxford/AstraZeneca and J&J vaccines, but every expert is urging people to understand that the risks of death and harm from Covid for most people far outweigh the risks of blood clots. The regulators in Europe and the UK have said these are rare events and backed use of the AZ vaccine to the hilt – and there is no reason to think it will be any different for the J&J jab. Unfortunately, these rare side-effects may do most harm to the chances of vaccinating the whole world any time soon.