By Clare Wilson
Use of the Johnson & Johnson covid-19 vaccine has been suspended in the US after six people experienced blood clots, out of 6.8 million who received the vaccine in the country. The cases seem to be similar to the rare blood clots seen in recipients of the Oxford/AstraZeneca vaccine, which has caused some countries to restrict its use.
The blood clot syndrome involves an unusual type of clot, often one that forms in the brain – called cerebral venous sinus thrombosis or CVST – coupled with low levels of platelets, small particles in the blood that stick together to make clots.
It has been seen mainly in people under about 60, and more often in women than men. But the sex difference may be because more women have been vaccinated, as they comprise more healthcare workers and care home staff. In an analysis of 79 UK cases seen after the Oxford/AstraZeneca jab, they occurred at the same rate in men and women, says Munir Pirmohamed, chair of the UK’s Commission on Human Medicines. The overall rate was four cases per million people who have received the vaccine in the UK.
It is unknown why younger people seem more at risk, but the age distribution is partly why some countries have said this vaccine should only be given to those above a certain age. The other reason is that older people are more at risk from covid-19 itself, so the benefit of the vaccine should outweigh the risk.
The six cases of CVST newly reported in recipients of the Johnson & Johnson vaccine, one of which was fatal, were all in women aged between 18 and 48.
Johnson & Johnson announced today it would delay the European roll-out of its product. “We have been working closely with medical experts and health authorities, and we strongly support the open communication of this information to healthcare professionals and the public,” the firm said in a statement.
What could be causing the clots? In the Oxford/AstraZeneca cases, many of those affected have tested positive for antibodies that bind to a molecule released by platelets, called platelet factor 4 or PF4. The vaccine may somehow trigger production of these antibodies, which cause multiple small clots to form in the blood and that can use up platelets, says Andreas Greinacher at the University of Greifswald in Germany. It resembles a syndrome in which similar antibodies can be triggered by the blood-thinning treatment heparin, says Greinacher, who is an expert on the heparin side effect.
Recently issued guidelines in some countries advise that a test for the platelet antibodies…
Read the full article in New Scientist
