Covid: AstraZeneca vaccine 79% effective with no increased blood clot risk – US trial

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The Covid-19 vaccine developed by Oxford University and AstraZeneca was 79% effective in preventing symptomatic illness in a large trial in the US, Chile and Peru, the company said on Monday, paving the way for it to apply for US approval.

The vaccine was 100% effective against severe or critical disease and hospitalisation and was safe, the drugmaker said on Monday, releasing results of the late-stage human trial study of more than 32,000 volunteers across all age groups.

The data will give credence to the British vaccine after results from earlier, separate late-stage studies raised questions about the robustness of the data.

It will also help allay safety concerns that have disrupted its use in the EU after a small number of reports of rare blood clots in people who had received the jab.

After briefly halting its use, many European countries have resumed using the product in their inoculation programmes after a regional regulator said it was safe, and several country leaders have been receiving the jab to boost confidence.

AstraZeneca said an independent safety committee conducted a specific review of the blood clots in the US trial, as well as cerebral venous sinus thrombosis (CVST), which is an extremely rare blood clot in the brain, with the help of an independent neurologist.

The London-listed company said the panel found “no increased risk of thrombosis or events characterised by thrombosis among the 21,583 participants receiving at least one dose of the vaccine. The specific search for CVST found no events in this trial”.

The partners will prepare the data to apply for approval from the US Food and Drug Administration (FDA), University of Oxford professor Sarah Gilbert told BBC radio. The preparation will take a few weeks, she added.

The results of the US trial have been long-awaited, delayed by the demands of the regulator that substantial numbers of people from older age groups and different ethnicities should be recruited to settle the question of how well it works in the over-65s.

Earlier trials, especially those run in the UK, did not recruit enough older people out of caution on the part of Oxford University, whose scientists wanted to be quite sure of its effects in younger people before they dosed others.

The Medicines and Healthcare products Regulatory Authority (MHRA) in the UK was satisfied with the limited data, but the European Medicines Agency took longer to approve it and some countries, such as Germany and France, initially made it available only to those under-65.

AstraZeneca, which ran the big US trial, will now hope any doubts are dispelled in the US and in Europe and that the age limits in Europe will be withdrawn. The US trial involved nearly 32,500 people, which is larger than any of their other trials of this vaccine, and about 20% were 65 or older. Nearly two-thirds were not in the best of health – 60% had underlying conditions including diabetes, severe obesity and heart disease, which would put them at serious risk if they caught the virus.

Yet the top line result is even better than in past trials, with 79% protected against symptomatic disease and no deaths in those vaccinated. The vaccine was even slightly more effective in the over-65s, at 80%.

Ethnicity made no difference, the trial found. In this interim analysis, approximately 79% were white/Caucasian, 8% black/African American, 4% Native American, 4% Asian, and 22% of participants were Hispanic. But the vaccine worked equally well in all.

Addressing the other issue that has damaged confidence in the vaccine in recent weeks, the company also points out that there were no serious side events such as blood clots among those who took part.

Oxford University and AstraZeneca will be hugely relieved by these results, which are the best they could hope for and should help to rebuild confidence in the vaccine.

The damage will not be instantly repaired. The data will now go to the US Food and Drug Administration (FDA), which will take a few weeks to decide whether to give the vaccine emergency approval. The company has worked with the FDA to ensure all the issues of concern are covered, so the next stage should go smoothly.

This trial is hugely important and not just for the US, which has unused stocks. The AstraZeneca vaccine was always intended to be the low-cost, easy-to-use vaccine for the whole world, manufactured in factories globally and the mainstay of the UN’s Covax programme. Although the WHO has approved it, the FDA is the regulator with the most influence, known for being the most difficult to please. If the FDA approves the vaccine, any lingering doubts on safety and efficacy are likely to fall away.

Supply, however, will then become an even bigger issue as every country embraces the vaccine and wants its share.



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