For higher age groups the benefit to risk ratio increased.Also on 7 April 2021, an interim statement from the WHO said its advisory body, GACVS, found any "causal relationship" between the rare blood clot cases and AZD1222 to be "plausible but is not confirmed".On 20 April 2021, the safety committee of the EMA (PRAC) found a "possible link to very rare cases of unusual blood clots with low blood platelets" for the Johnson & Johnson Janssen vaccine; and required that these rare events, similar to those noted for AZD1222, should be listed as a very rare side effect. The EMA states the overall risk-benefit for the Janssen vaccine remains positive.On 16 December 2021, the US Centers for Disease Control and Prevention (CDC) recommended the Moderna and Pfizer­­-BioNTech vaccines should be preferred over the Janssen vaccine, following growing concerns about rare blood clots. Janssen should still be offered to people who specifically request it. History
Organizations
Global vaccine safety comes under the remit of the World Health Organization (WHO), and in particular its Global Advisory Committee on Vaccine Safety (GAVCS). Other drug regulatory agencies significantly involved include:
European Medicines Agency (EMA), the regional regulatory authority for the EU. Medicines and Healthcare products Regulatory Agency (MHRA), the medical authority for the United Kingdom. Paul Ehrlich Institute (PEI), a German federal agency supervised by the Federal Ministry of Health with expertise in vaccines and biomedicines. It is a WHO collaborating centre.
"Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination". N Engl J Med. 384 (22): 2124–30. doi:10.1056/NEJMoa2104882. PMC 8112568. PMID 33835768. Scully M, Singh D, Lown R, Poles A, Solomon T, Levi M,  et al. (June 2021). "Pathologic Antibodies to Platelet Factor 4 after ChAdOx1 nCoV-19 Vaccination". N Engl J Med. 384 (23): 2202–11. doi:10.1056/NEJMoa2105385. PMC 8112532. PMID 33861525. External links
EMA press conference 7th April on YouTube