PARIS : Several European countries are considering mixing up COVID-19 vaccines for citizens who received a first dose of AstraZeneca's shot, an unprecedented move that highlights challenges for governments struggling to tame fresh rises in infections.Vaccination programmes have been upset after a small number of reports that recipients of the AstraZeneca inoculation have suffered extremely rare blood clots, leading some countries worldwide to suspend its use out of caution.A senior official for the European Medicines Agency (EMA) said in an interview published on Tuesday there was a link between the vaccine and rare blood clots in the brain but the possible causes were still unknown.The EMA later said in a statement that its review of the.