The European Drug Administration (EMA) said on April 9 that the authorities were reviewing cases of blood clots that occurred after being vaccinated against Johnson. It is reported that four people who received Johnson vaccine developed rare thrombotic symptoms with thrombocytopenia. One of the cases occurred during clinical trials. At the time, Johnson said it found no evidence of a problem with the vaccine. Three other cases have occurred in the United States, where nearly 5 million people have received the vaccine. It is reported that after the AstraZeneca vaccine, the European Drug Administration examined the symptoms of thrombus after the vaccination of the second COVID-19 vaccine. Earlier, the FDA announced on the 7th that thrombosis was a "very rare" side effect of AstraZeneca vaccination. At present, many European countries have adjusted the scope of AstraZeneca vaccination population. Johnson said in a statement that it was working with regulators around the world to evaluate data on thrombus symptoms and reiterated that there was "no clear causal relationship" between Johnson vaccination and thrombosis, the report said.