While Covid-19 vaccines have been credited with saving tens of thousands of lives, there have also been health scares linked to them.
The latest involves the Johnson and Johnson vaccine and a rare neurological condition, Guillain-Barre syndrome (GBS).
This week the US Food and Drug Administration added a warning about GBS to its guidelines for healthcare providers administering the vaccine, which is also known by its brand name, Janssen.
Here we look at the condition and consider its apparent association with the shot.
What is Guillain-Barre syndrome?
Guillain-Barre syndrome, which the UK’s National Health Service (NHS) says is pronounced “ghee-yan bar-ray”, is caused by the immune system attacking the body’s nerves. Cases frequently follow a bacterial or viral infection, including influenza.
Early symptoms include numbness, weakness, pain and balance problems, which may worsen over several weeks, with the feet, hands and limbs most affected.
In some cases, sufferers find walking, swallowing and even breathing difficult, according to guidance from the NHS, and as symptoms spread, movement as a whole may prove difficult.
Various treatments are available, including blood filtering called plasma exchange, or the administration of an intravenous substance produced from donated blood.
Hospital stays of weeks or months are typical and there is a risk of death. Some people are left with long-term complications. However, most patients recover fully.
Children can develop the condition, although it is more common in adults, especially men. In a typical year there are about 3,000 to 6,000 cases in the US alone.
Is there a link to vaccination?
According to the US Centres for Disease Control and Prevention there have been about 100 cases of GBS in the country among 12.8 million people who received the Johnson and Johnson vaccine. Of these, 95 were serious, with one fatal.
Symptoms typically developed two weeks after vaccination and men over the age of 50 were most affected.
Last month there were reports of a handful of cases of GBS in the Nottingham area of central England in people who had received the Oxford-AstraZeneca vaccine. Also some recipients in India and Australia have developed the condition.
The Johnson and Johnson and Oxford-AstraZeneca vaccines are based on similar technology, being viral vector vaccines made from a harmless adenovirus that delivers coronavirus genetic material into cells.
Is vaccination still safe?
While the Johnson and Johnson vaccine does appear to increase the chance of developing GBS, the US data indicate that fewer than one recipient in 100,000 falls ill.
As with the Oxford-AstraZeneca vaccine, regulators have not recommended against use of the vaccine because of GBS.
“That’s a significant risk and it’s a very serious condition, but at the same time, for the average person, no doubt vaccination is beneficial,” said David Taylor, professor emeritus of pharmaceutical and public health policy at University College London.
Balanced against the risks of vaccination are the much higher risks from developing Covid-19, which may itself be a risk factor for GBS, although findings are contradictory.
A study from last year looking at cases in England during the first wave of the pandemic found that there were actually fewer reports of the condition in 2020 compared with previous years.
However, Dubai Medical Journal earlier this year reported GBS in a 72-year-old man in Kuwait with Covid-19.
“Neurologists should be aware of GBS as a potentially serious complication associated with Covid-19,” the researchers concluded.
Are there other risks associated with Covid-19 vaccination?
The Johnson and Johnson and Oxford-AstraZeneca vaccines have been linked to a syndrome called immune thrombotic thrombocytopenia, which causes potentially fatal blood clots.
Although such cases have been extremely rare, the risk has caused some countries to impose age restrictions on recipients of these vaccines, with younger people often offered an alternative.
Two other vaccines, the Moderna and Pfizer jabs, based on mRNA technology, have been linked to a rare type of heart inflammation called myocarditis, with teenage boys and young men most at risk.
A report from Harvard Health Publishing this month said there had been about 1,000 cases among millions of people vaccinated.
“The majority of cases have been mild. Experts are still gathering information, but as of this writing, 79 per cent of teenagers and young adults who experienced this had recovered,” wrote Dr Claire McCarthy, a paediatrician at Boston Children’s Hospital and an assistant professor of paediatrics at Harvard Medical School.
She said there was a risk of myocarditis, and other complications, from Covid-19, and the recommendation was for vaccination to continue.