CHICAGO / 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 shots could contribute at risk.
In Europe, health regulators said last week there was a possible link between the AstraZeneca Plc vaccine and 169 cases of a rare cerebral blood clot known as cerebral venous sinus thrombosis (CVST), accompanied by a low platelet count in blood, 34 million shots. administered in the European Economic Area.
The U.S. Food and Drug Administration on Tuesday recommended a temporary cessation of Johnson & Johnson vaccine use after reporting six cases of CVST in women under 50 among about 7 million people who were 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 essentially harmless. Viruses are used as vectors to transmit instructions to human cells to produce proteins that are on the surface of the coronavirus, preparing the immune system to produce antibodies that fight the real virus.
Scientists are working to find the potential mechanism that explains blood clots. A major hypothesis appears to be that the vaccines are triggering a rare immune response that could be related to these viral vectors, FDA officials said in a briefing Tuesday.
The U.S. agency will analyze data from clinical trials of several vaccines that use these viral vectors, including the J&J Ebola vaccine, to look for clues.
None of the previous vaccines using viral vectors have been administered near the scale of the AstraZeneca and J&J COVID-19 shots, which may explain why a potential link to blood clots only materialized during these vaccination programs. massive.
The technology has also been used in coronavirus vaccines developed in China and Russia.
Peter Marks, director of the FDA’s Center for Biological Evaluation and Research, was reluctant to say that blood clots produce a “class effect” shared by all vector adenovirus vaccines, but he sees a marked similarity in cases.
“It’s already clear to us that what we’re seeing with the Janssen (J&J) vaccine looks very similar to what we were seeing with the AstraZeneca vaccine,” Marks said. “We still can’t make any broad claims, but they obviously belong to the same general class of viral vectors.”
‘AT THE BEGINNING’
In Europe, scientists are exploring several hypotheses, including those that more broadly analyze how the SARS-CoV-2 virus itself affects blood clotting.
A team from the Netherlands plans to conduct laboratory studies that expose specific types of cells and tissues to vaccines and monitor their reaction. They will also explore whether the risks can be further limited by reducing the dose of vaccine.
“There are many hypotheses and some may play a role,” said Eric van Gorp, a virologist at Rotterdam’s Erasmus Medical Center. “We’re at the beginning and, as in the investigation, we may be able to find the clue at once or step by step.”
Other scientists were shocked by the parallelism between the features of J&J and AstraZeneca.
Danny Altmann, a professor of immunology at Imperial College London, said similar blood clotting incidents associated with both “are clearly noteworthy in defining the mechanism”. There were no signs of these problems with vaccines developed by BioNTech SE with Pfizer Inc or Moderna Inc using a different technology.
“It would be interesting to know more about Sputnik V, also a similar adenovirus vaccine,” Altmann said. The Russian vaccine developed by the Gamaleya Institute in Moscow uses two different viruses from the human cold, including the Ad26 virus in the J&J trait.
The problem could also affect China’s CanSino Biological adenovirus vector vaccine, experts said.
Examining whether there is any common link to 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 City.
Moore, who attended an informal White House meeting with other scientists on Tuesday, said the FDA and U.S. Centers for Disease Control and Prevention are working closely with European health officials to determine if vaccine-related syndromes AstraZeneca and J&J are the same.
An important clue may lie in the fact that the reported events usually appear about 13 days after the shot, which is the period in which antibodies could be expected to appear.
“This is speculation, but the timing of something happening after 13 days on average suggests an immune response to a component of the vaccine,” Moore said.
Such research could take years. But, like the same vaccines that occurred in record time, Moore believes there will be so much effort in the investigation that it is likely to be resolved in a few weeks.
“It’s so clearly important,” he said.
Reports by Julie Steenhuysen and Kate Kelland; Additional reports by Michael Erman Maplewood, New Jersey; Edited by Michele Gershberg and Bill Berkrot