CHICAGO v LONDON (Reuters) – With two COVID-19 vaccines now under control for possible links to very rare cases of blood clots in the brain, US government scientists are focusing on whether the specific technology behind the blows could help risk.
In Europe, health regulators said last week that there was a possible link between the AstraZeneca Plc vaccine and 169 rare cases of cerebral blood clot known as cerebral venous sinus thrombosis (CVST), accompanied by a low number of platelets in the blood, out of 34 million photos administered in the European Economic Area.
The US Food and Drug Administration on Tuesday recommended a temporary cessation of Johnson & Johnson vaccine after six cases of CVST were reported in women under the age of 50, among about 7 million people shot in the United States.
Both vaccines are based on a new technology that uses adenoviruses, which cause the common cold, which have been modified to make them harmless. Viruses are used as vectors to carry instructions for human cells to produce proteins found on the surface of the coronavirus, priming the immune system to produce antibodies that fight the real virus.
Scientists are working to find the potential mechanism that would explain the blood clots. A major hypothesis appears to be that vaccines trigger a rare immune response that could be linked to these viral vectors, FDA officials said in a briefing Tuesday.
The US agency will analyze data from clinical trials of several vaccines that use these viral vectors, including J & J’s Ebola vaccine, to look for clues.
None of the previous vaccines using viral vectors were administered near the scale of AstraZeneca and J&J COVID-19 photographs, which may explain why a potential link to blood clots materialized only during these mass vaccination programs.
The technology has also been used in coronavirus vaccines developed in China and Russia.
Peter Marks, director of the FDA’s Center for Biological Assessment and Research, was reluctant to say that blood clots emit a “class effect” shared by all vector adenovirus vaccines, but he sees a marked resemblance in cases.
“It’s already clear to us that what we see with the Janssen (J&J) vaccine looks very similar to what we see with the AstraZeneca vaccine,” Marks said. “We can’t make a broad statement yet, but they obviously come from the same general class of viral vectors.”
‘AT THE BEGINNING’
In Europe, scientists are exploring a number of hypotheses, including more broadly how the SARS-CoV-2 virus itself affects blood clotting.
A team from the Netherlands intends to carry out laboratory studies that expose specific types of cells and tissues to vaccines and to monitor how they react. They will also explore whether any risks could be further limited by reducing the dose of the vaccine.
“There are many hypotheses, and some of them could play a role,” said Eric van Gorp, a virologist at Erasmus Medical Center in Rotterdam. “We are at the beginning and, as in research, it is possible to find the clue all of a sudden or it may go step by step.”
Other scientists have been struck by the parallel between J&J and AstraZeneca photos.
Danny Altmann, a professor of immunology at Imperial College London, said the similar blood clotting incidents associated with both “are clearly noteworthy for defining the mechanism”. There were no signs of such problems with vaccines made by BioNTech SE with Pfizer Inc. or Moderna Inc. using a different technology.
“It would be interesting to learn more about Sputnik V – also an adenovirus-like vaccine,” Altmann said. The Russian vaccine developed by the Gamaleya Institute in Moscow uses two different human cold viruses – including the Ad26 virus in the J&J shot.
The problem could also affect China’s CanSino Biological adenovirus vector vaccine, experts said.
Examining whether there is a common link with adenoviruses is “reasonable speculation and is a line of research and investigation. But that doesn’t mean it’s proven, “said John Moore, a professor of microbiology and immunology at Weill Cornell Medical College in New York.
Moore, who attended an informal White House briefing with other scientists on Tuesday, said the FDA and the U.S. Centers for Disease Control and Prevention are working closely with health officials in Europe to determine whether AstraZeneca vaccine syndromes and J&J are the same.
An important indication may be that the reported events usually occur approximately 13 days after the shooting, which is the period when antibodies can be expected to appear.
“This is speculation, but when something happens after about 13 days on average suggests an immune response to a component to the vaccine,” Moore said.
Such investigations could take years. But like the vaccines themselves, which were produced in record time, Moore believes so much research will be done that it will most likely be resolved in a few weeks.
“It’s so clearly important,” he said.
Reporting by Julie Steenhuysen and Kate Kelland; Additional reporting by Michael Erman Maplewood, NJ; Edited by Michele Gershberg and Bill Berkrot