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AZ vaccine 100% effective against hospitalisation in US trial which found no link to blood clots


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The AstraZeneca Covid vaccine is 100% effective in preventing severe illness and hospitalisations, while presenting ‘no increased risk’ of blood clots, the company’s phase-3 trial for the US market has concluded.

The trial involved over 32,000 volunteers of all age groups in the US, Chile and Peru, and saw participants receive either two doses of the Oxford/AstraZeneca vaccine, or placebo jabs, at four-week intervals. 

There were ‘no safety concerns’ reported in the study, which found the vaccine was 79% effective against symptomatic Covid-19 and offered complete protection against ‘severe or critical disease and hospitalisation’. 

It added that the vaccine’s efficacy was ‘consistent’ across different ethnicities and age groups.

The company said, in particular, the trial found ‘no increased risk of thrombosis or events characterised by thrombosis’ in the 21,500 participants receiving at least one dose of the vaccine.

This comes as the European Medicines Agency (EMA) concluded its safety review of the AstraZeneca vaccine on Thursday last week, saying it ‘likely reduces’ the risk of blood clots overall.

Oxford trial lead investigator Professor Andrew Pollard, a professor of paediatric infection and immunity, said: ‘These results are great news as they show the remarkable efficacy of the vaccine in a new population and are consistent with the results from Oxford-led trials.

‘We can expect strong impact against Covid-19 across all ages and for people of all different backgrounds from widespread use of the vaccine.’  

AstraZeneca said it will continue to analyse the data and will submit the analysis to the US Food and Drug Administration for emergency use authorisation in the coming weeks. The full data will also be published in a peer-reviewed journal, it added.

Last week, the UK medicines regulator said patients with a headache lasting more than four days after their Covid vaccination should ‘seek medical attention’ in a bid to rule out thrombosis.

Earlier in the week, the MHRA had urged patients to continue to turn up for their AstraZeneca Covid vaccination amid ‘unconfirmed’ blood clot reports.

However, GPs leading vaccination sites told Pulse that many patients had already been put off by the news of the European suspensions of its usage and were turning down the jab or not turning up at all.