The death of a woman in New Zealand was “probably” due to an extremely rare side effect of the Pfizer vaccination, authorities in the country said this week.

The Covid-19 Vaccine Independent Safety Monitoring Board said the case has been referred to a coroner and “the cause of death has not yet been determined”. If confirmed, it would be the first death in New Zealand linked to a coronavirus vaccine.

But either way, the latest evidence clearly shows that the risks of Covid are much greater than those potentially posed by the jab.

Let’s take a look.

Covid poses much greater heart inflammation risk

It’s thought that the New Zealand woman died of myocarditis, an inflammation of the heart muscle. While we don’t yet know whether the Pfizer jab caused her illness, it’s not the first time a link has been suggested between the two.

The UK medicines regulator, the MHRA, says that there has been a “recent increase in reporting of these events in particular with the Pfizer/BioNTech and Moderna vaccines, with a consistent pattern of cases occurring more frequently in young males and shortly after the second dose of the vaccines.”

However, the regulator stresses that “these reports are extremely rare, and the events are typically mild with individuals usually recovering within a short time with standard treatment and rest”.

“Anyone who experiences new onset of symptoms such as chest pain, shortness of breath or feelings of having a fast-beating, fluttering, or pounding heart” is encouraged to seek medical attention.

We’ve recently had some more precise figures about a possible link between myocarditis and the Pfizer jab.

A very large study from Israel published last week in the New England Journal of Medicine estimates that for every 100,000 people to receive the vaccine, we’d see an extra 2.7 cases of the condition above what would have been expected if those same people had not been jabbed.

But crucially, Covid-19 itself is a much greater risk factor. The researchers estimate that among 100,000 people who test positive for the virus, there would be an additional 11 cases of heart inflammation compared to the same number of uninfected people.

What about stroke risk?

Another large study, this one published in the British Medical Journal by scientists at the University of Oxford, considers a possible link to ischaemic stroke.

By their calculations, if 10 million people received the Pfizer jab, we might see 143 more cases of this type of stroke than usual.

Though again, the risk is much higher with Covid: among 10 million people who test positive for Covid, there’d be an additional 1,699 cases of ischaemic stroke.

While the UK and Israel studies are not directly comparable, we might roughly translate that as 1.4 extra cases of ischaemic stroke per 100,000 Pfizer recipients, versus 17 extra cases per 100,000 people with the virus.

Other conditions?

The Israel study found an increased rate of lymphadenopathy (swollen lymph nodes) among Pfizer recipients: an extra 78.4 cases per 100,000 people jabbed. The condition usually resolves on its own within two weeks.

The researchers also calculate a slightly increased risk of appendicitis among Pfizer recipients at 5 additional cases per 100,000.

However, the analysis also found that testing positive for coronavirus “substantially” increases the risk of several other very serious conditions.

Among 100,000 people infected with the virus, the researchers expect 166 extra cases of abnormal heart rhythm, 125 additional acute kidney injuries, 61 more people suffering a blood clot in the lungs, 43 extra cases of deep-vein thrombosis, 25 extra cases of a blood clot in the heart, 11 more cases of inflammation of the heart lining, and eight more instances of brain haemorrhage.

Importantly, the researchers found no link between any of these conditions and the Pfizer jab.

Can we compare Pfizer and AstraZeneca?

Pfizer’s is not the first Covid vaccine to attract safety concerns.

In April, the Joint Committee on Vaccination and Immunisation (JCVI) advised the UK government to offer adults under 30 an alternative to the AstraZeneca jab after fears it was linked to an extremely rare blood clot combined with low platelets. Since then, the recommendation has been expanded to include people in their thirties too.

The latest Oxford University study gives us some up-to-date information on the two jabs’ possible link to these blood clots and conditions.

Out of 10 million AstraZeneca recipients, the researchers estimate an extra 107 cases of thrombocytopenia (very low platelets, which on rare occasions can be fatal), 66 extra cases of venous thromboembolism (blood clot in the veins) and seven extra cases of CVST (a type of clot affecting the brain).

With all three conditions, the risks posed by Covid were much greater: out of 10 million people with the virus, there’d be 934 extra cases of thrombocytopenia, 12,614 extra cases of venous thromboembolism and 20 extra cases of CVST.

The Oxford study found no association between these conditions and the Pfizer jab. Though Pfizer recipients were more likely to suffer an ischaemic stroke, which was not linked to AstraZeneca.

It’s tempting to tot up the possible side effects linked to the two jabs from the evidence we’ve looked at to try and work out which of them is more risky. But neither the Oxford nor the Israel study claims to have covered an exhaustive list of all potential side effects associated with either jab. For example, the UK researchers did not publish results on myocarditis, and the Israel study didn’t consider AstraZeneca recipients. So we should avoid back-of-the-envelope calculations and wait for more robust analysis.

In the meantime, the message from both these studies, the UK medicines regulator and the New Zealand health authorities is that being vaccinated against Covid-19 is much safer than catching the virus.