US health officials paused distribution of the Johnson & Johnson Covid-19 vaccine as scientists investigate the potential link between rare cases of blood clots and the potentially life-saving vaccine. Currently, the clotting “syndrome” appears to affect less than one in a million people who receive the vaccine.

Among more than 7.2m vaccine doses, scientists are investigating six cases of women between 18 and 48 who developed a rare blood clot, one that critically needs to be treated without heparin, a common blood thinner.

The pause has caused concern worldwide, among health professionals and ordinary citizens. Here are some of the key questions being asked:

What is happening with the J&J vaccine?

US health officials “paused” distribution while a potentially serious clotting syndrome is investigated. Among the nearly 7 million people who received the vaccine, just six cases were discovered.

In all six cases, the potential side-effect occurred between six and 13 days post-vaccination, after the period when people’s common and usually mild flu-like side-effects are resolved. Health officials advised that people suffering from a severe headache, leg or abdominal pain or shortness of breath should tell their doctors if they were recently vaccinated.

Officially the clotting syndrome is called “cerebral venous sinus thrombosis” with “thrombocytopenia”. This technical mouthful means the cases involved a clot in the brain with the presence of low counts of platelets, the blood element which allows for clotting. The presence of a low platelet count is especially important, because it means doctors should not treat the clots as they commonly do, with a blood thinner called heparin, which in this instance could be dangerous.

That sounds scary. Should I be worried?

Health authorities said people who received the Johnson & Johnson vaccine more than six days but less than three weeks ago should be aware of the potential symptoms of this syndrome, even as authorities investigate whether it is indeed linked to the vaccine.

If you are experiencing symptoms of this syndrome, you should seek medical attention. However, health authorities have stressed this syndrome is exceedingly rare. In other words, be aware but do not worry.

The current rate of this syndrome is less than one in 1 million. That could change as more cases are recognized and reported. Assuming the rate does not change dramatically, it is in the same range as this kind of clotting (without low platelet count) in the population – between two and 14 people per million.

Notably, cerebral venous sinus thrombosis has also occurred rarely in young people who developed Covid-19. In a June series of case studies, researchers with the American Journal of Neuroradiology found just three patients who suffered from these clots as a complication of Covid-19. All three died.

To put risk into an even broader context, we can look at the scientific meaning of the word “rare”. Rare diseases in the US are classified as those which affect 86 people per 100,000. To match the rate of 86 per 100,000, more than 5,800 people would have needed to be affected among the 6.8m vaccine doses given.

This particular clotting syndrome is also rarer than a blood clot from hormonal contraceptives (roughly one in 100); the risk of being involved in a fatal car accident (roughly one in 10,000) and is currently rarer than getting struck by lightning (roughly one in 500,000).

Again, one of the reasons authorities see it as so important to notify the public is because the low platelet count associated with the blood clots means doctors must treat it without heparin, or risk worsening a patient’s condition.

Of course, another measure of relative risk would be to compare the risk of death from Covid-19 with the risk of death from the clotting syndrome.

Before the disastrous winter surge of Covid-19, the rate of death from Covid-19 in the US was 27.2 per 100,000 people, according to a study published in the Journal of the American Medical Association. That rate is among the worst in the industrialized world. Right now, scientists know of one death from the blood clot being investigated, among more than 7.2 million people who received the vaccine.

In other words, you are still at higher risk of dying of Covid-19 in the US, than your are of this syndrome, whose connection to the vaccine is still being investigated.

Has this kind of syndrome been seen before?

Yes, authorities said it bears a resemblance to a clotting syndrome with low platelet count seen among recipients of the AstraZeneca vaccine in Europe and Australia. As of 4 April, more than 222 cases of blood clots have been identified among 34 million people who received the vaccine.

Although rates have differed throughout the world, Australian authorities found between four and six people per 1 million were affected by the similar syndrome, with higher rates in some Scandinavian countries.

Both AstraZeneca and Johnson & Johnson share a vaccine technology, called a “platform”, which uses a weakened version of a cold virus to deliver the genetic payload of the coronavirus to the body. This platform is called viral vector technology. There are important differences between the vaccines, but scientists said a link is being investigated.

As for other vaccines authorized in the US, more than 184m doses of the Moderna and Pfizer vaccines have been administered in the US. There have been no “red flag” signals to trigger a pause.

What is a pause?

A “pause” allows officials to publicize the potential side-effect, allows doctors time to understand how to treat it and will probably result in more reporting of potential cases. If scientists can find commonalities between the women who developed such clots, it may also help identify people at greater risk for the syndrome.

Scientific authorities also hope it will show the public their commitment to transparently investigating serious outcomes, and to publicly balancing risks and benefits of newly developed vaccines.

Balancing the risk and benefit will happen publicly at a meeting of the Centers for Disease Control and Prevention’s vaccine practices advisory committee, a group of independent experts. The committee is scheduled to meet on Wednesday afternoon.

One potential outcome of that meeting is that officials issue new guidance about the vaccine. The pause and review is likely to happen over a period of days, rather than weeks, officials said on Tuesday. Johnson & Johnson has said while the syndrome is investigated, it will delay the rollout of its vaccine in Europe.

Is the pause going to affect vaccine distribution?

Yes, it could have an outsized impact on vaccine distribution, though not in the US. The biggest impact on vaccination could be global. Johnson & Johnson’s vaccine is easy to store, easy to administer and requires only one shot. That holds huge promise for vaccinating countries around the world that do not have ultra-cold chain infrastructure, such as is required for Moderna and Pfizer’s vaccines.

The Biden administration and health authorities have both said they believe there is more than enough vaccine available from Moderna and Pfizer to inoculate the American public. Notably, the pause may hit rural and isolated communities in the US, where officials had hoped to deploy it.

The pause could also affect vaccine distribution in a different way – by elevating vaccine hesitancy. The news of the investigation of clotting syndromes and the vaccine is likely to inflame conspiracy theorists, who often use anecdotal stories of harm to obscure relative risk. That can give certain activities an outsized appearance of risk.

It is a key reason why the personal stories of parents whose children developed autism after receiving a vaccine – even though there is no link – have proved effective propaganda for people who seek to profit by undermining vaccine confidence.

A huge proportion of US adults need to be vaccinated to reach herd immunity, the point at which the virus fizzles out when it cannot find new hosts. If people feel uneasy about taking the vaccine, it will make it harder to vaccinate everyone. How health authorities balance these nuanced priorities will ultimately determine the success of the vaccine campaign.

This content first appear on the guardian

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