The AstraZeneca vaccine may increase the risk of serious neurological disease of Guillain-Barré syndrome (GBS) with scientists looking to see if the vaccine with this vaccine has acted as a Trojan horse in the onset of the syndrome.
GBS syndrome is a rare condition that causes muscle numbness and pain and can impede movement, walking, swallowing and, sometimes, even breathing.
It is usually caused by the Campylobacter gastroenteritis bacterium, which has a slightly human-like surface coating, and so can sometimes cause the body to attack its own nerves instead of invading the germs, leading to GBS.
According to a report in the British Telegraph, scientists at University College London (UCL) found an increase in GBS cases in the first two to four weeks after the AstraZeneca vaccine, but not in other vaccines, such as Pfizer or Moderna.
Like many vaccines, the Oxford vaccine uses an attenuated adenovirus chimpanzee to carry the coronavirus protein throughout the body, and scientists have speculated that an adenovirus reaction may be responsible for the increased incidence.
The adenovirus usually causes the common cold, but scientists are beginning to believe that it can also mimic human cells in a similar way to Campylobacter, confusing the immune system to attack the body.
Lead author Professor Michael Lunn (UCL Queen Square Institute of Neurology) said: "At this time we do not know why a vaccine can cause these very small increases in GBS.
"Non-specific immune activation may occur in susceptible individuals, but if this were the case, similar risks could apply to all types of vaccines.
"It is therefore reasonable to suggest that the monkey adenovirus vector, which is often used to develop vaccines, including AstraZeneca, may be responsible for the increased risk."
Unusual rise in GBS reports
Adenovirus-based vaccines are used against a wide variety of pathogens, tuberculosis, HIV and malaria.
GBS affects around 1.500 people in the UK each year and 30 to 40 per cent of cases have no known cause, leading researchers to suspect that adenovirus may be a factor.
During the 1976 swine flu vaccination campaign in the United States, there was a small increase in the GBS associated with the flu vaccine at the time, leading scientists to wonder if Covid vaccines could have a similar effect.
To find out, UCL researchers conducted a population-based NHS data study in England to track GBS versus vaccine development rates.
From January to October 2021, 996 GBS cases were recorded in the UK National Immunoglobulin Database, but there was an unusual increase in GBS reports between March and April 2021.
For those two months there were about 140 cases per month compared to historical rates of about 100 per month - an increase of 40 percent.
The analysis showed that 198 GBS cases (20 percent) occurred within six weeks of the first dose vaccination. Covid-19 in England.
In total, after a first dose of the AstraZeneca vaccine, there were an excess of 5,8 GBS cases per million doses of the vaccine, equivalent to
with an absolute total excess between January-July 2021 between 98-140 cases.
The rate is still significantly lower than the GBS rate associated with Campylobacter at 1.000.
The data suggest that the Johnson & Johnson vaccine increases the risk of GBS
Recent US data also suggest that the Johnson & Johnson Janssen vaccine - which also uses an adenovirus entry system - increases the risk of GBS at levels similar to the AstraZeneca vaccine.
"We know that Pfizer and Moderna do not cause BDS, but Johnson & Johnson and AstraZeneca do and the only community link is an adenovirus carrier," added Professor Lund.
"Johnson & Johnson are not the same because they use a human adenovirus, but they are similar and the effects are widespread because adenoviruses are used in many vaccines and genetic therapies.
"The benefits of these vaccines and drugs are huge and the risk is small and there are not many viral vectors you can use, but it is good for the public to be aware of the risks.
"And theoretically, if we know which virus is causing GBS, we can turn it off and maybe we can prevent the disease from progressing."
The new research was published in the journal Brain.
Vaccine benefits "continue to outweigh potential risks"
An AstraZeneca spokesman said: "Guillain-Barre syndrome (GBS) has been reported very rarely after vaccination with Vaxzevria. Each type of vaccination is a known risk factor for GBS, and the manuscript notes that the small number of GBS cases appears to be similar to the increases previously observed in other mass vaccination campaigns.
"It should also be noted that in the United Kingdom, Vaxzevria was given to more people than any other vaccine during the time frame studied in the manuscript.
"The study notes that the small number of cases should be compared to the number of infections, hospitalizations and deaths that our vaccine has prevented due to Covid-19. Current estimates show that the vaccine has helped prevent 50 million cases worldwide Covid-19, five million hospitalizations and has saved more than one million lives.
"The EMA and other international bodies, including the WHO, have all stated that the benefits of vaccination outweigh the potential risks."