Johnson & Johnson and AstraZeneca are conducting early research into whether modifications to their Covid-19 vaccines could eliminate or reduce the risk of rare blood clots linked to the shots, Reuters report, quoting the Wall Street Journal.
WSJ on Tuesday reported that outside scientists and AstraZeneca's partner, the University of Oxford, were also involved in the efforts.
Both vaccines have been linked to the risk of blood clots, though regulators have said that benefits of the vaccines largely outweigh the risks.
