AstraZeneca Covid-19 vaccine trials resume in UK after temporary halt

The Serum Institute in India had also paused its phase 3 trials of the AstraZeneca COVID-19 vaccine. The drug manufacturer is now awaiting approval from the Drugs Controller General of India to resume its trials in India. 

Sep 14, 2020 19:35 IST
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AstraZeneca has partly resumed its COVID-19 vaccine trials after a temporary pause. The drug manufacturer announced on September 12, 2020 that the last-stage clinical trials of its coronavirus vaccine have resumed in the UK after British regulator gave its go ahead after deeming it safe.

The AstraZeneca COVID vaccine trials in other countries including the United States, however, continue to remain paused while AstraZeneca works with national health authorities to conclude its safety. 

AstraZeneca had put the last phase of clinical trials of the Oxford COVID-19 vaccine on hold on September 8, 2020 after one of the participants fell ill in the United Kingdom. AstraZeneca had described the pause as a "routine" pause in the case of "an unexplained illness".

The Serum Institute in India had also paused its phase 3 trials of the AstraZeneca COVID-19 vaccine. The drug manufacturer is now awaiting approval from the Drugs Controller General of India to resume its trials in India. 


The AstraZeneca-Oxford COVID vaccine is one of the leading COVID-19 vaccine candidates, whose trials are being conducted in multiple nations including India and the United States. The outcome of vaccine trials is being closely watched across the world.

The Oxford vaccine is seen as a strong contender among dozens of vaccines being developed globally, as the phase I and II trial results showed that the vaccine offers double immunity against COVID-19. The vaccine candidate moved to phase III trials a few weeks back. 

AstraZeneca COVID-19 vaccine phase 3 trials 

The AstraZeneca-Oxford COVID vaccine recently moved to phase 3 clinical trials involving over 30,000 participants in the United States as well as in the United Kingdom, South Africa and Brazil. The phase 3 trials of vaccines usually involve thousands of participants and last for several years.

However, the phase 3 trials of the Oxford COVID-19 vaccine were to be completed by September and there were high hopes that the vaccine might be the first one to come in the market, following successful phase 1 and 2 trials.

Significance of Phase 3 trials

The last-phase of trials are considered the most important study phase to establish the safety of a vaccine because of their large size. During the final stage of testing, the researchers look for all signs of possible side effects, even the less common ones, that may have gone undetected in the earlier trials. 

The trials also effectiveness assess by tracking who gets sick and who doesn't between patients getting the vaccine and those receiving a dummy shot.

Trial halt temporary?

The AstraZeneca issued a statement on September 8, 2020 saying that late-stage studies of its vaccine candidate are on temporary hold while the company investigates whether a recipient's "potentially unexplained" illness is a side effect of the shot.

The company said in its statement that its standard review process triggered a pause to vaccination to allow review of safety data. However, the company didn't reveal any information about the possible side effect except to call it "a potentially unexplained illness".

The company also pointed out that it is possible that the illness could be a coincidence, as all sorts of illnesses could arise in studies involving thousands of people. The company is working to expedite the review of the single event to minimize any potential impact on the trial timeline.

AstraZeneca Vaccine Trials in India halted as well?

AstraZeneca has tied up with private vaccine manufacturer Serum Institute of India (SII) to manufacture doses of the vaccine once it gets the required approval. The Serum Institute is also conducting clinical trials of the vaccine in India. The institute had earlier sought regulatory licensing from the authorities for the same.

Speaking on the pause in UK trials of the vaccine, Serum Institute of India stated that it cannot comment on it but they have been paused for further review and hope restart soon. As far as Indian trials are concerned, the Serum Institute confirmed that it is continuing and they have faced no issues at all. 

When will clinical trials resume?

The Oxford University team described the pause in the clinical trials as routine, as any time a volunteer is admitted to the hospital and the cause of their illness is not immediately known it triggers the study to be put on hold. 

This is the second time that the Oxford vaccine trials have been put on hold after the first volunteers were administered the vaccine in April. An Oxford University spokesperson stated that in case of large trials, illnesses will happen by chance but must be independently reviewed.

UK's medical regulator, Medicines and Healthcare products Regulatory Agency, will soon make the final decision on restarting the trials after the cause of illness of the person is correctly known and understood. Till then, all international vaccination sites in the UK, US, Brazil and South Africa have been put on hold. 

Why is the pause alarming?

The Oxford vaccine trial is the most closely watched COVID-19 vaccine trials in the world. The vaccine is the most promising vaccine candidate of all and hence, it has been receiving massive global attention. However, such temporary holds are not unheard of in vaccine trials, especially such large medical studies, as investigating any serious or unexpected reaction is a mandatory part of safety testing.

Other Vaccines in final stage of trials 

Two other COVID-19 vaccine candidates are in final-stage trials in the United States- one developed by Moderna Inc. and the other developed by Pfizer and Germany's BioNTech. These two vaccines work differently from the AstraZeneca-Oxford COVID vaccine and their studies have already recruited about two-thirds of the needed volunteers.


The development came the same day when AstraZeneca along with 8 other COVID-19 vaccine developers announced a historic pledge to uphold scientific and ethical standards in the search for a vaccine. The firms in the unusual pledge vowed to only apply for regulatory approval after vaccines have gone through three phases of clinical study. The pledge was aimed to reassure the public about the safety of their vaccines.  

The other eight firms who signed the pledge along with AstraZeneca include Moderna, Pfizer, BioNTech, Johnson & Johnson, GlaxoSmithKline, Merk, Moderna, Sanofi and Novavax. All nine vaccine developers pledged to always make the safety and well-being of vaccinated individuals our top priority. 

The announcement follows US President Donald Trump's statement that he wants a vaccine available in the US before the US Presidential Elections on November 3, 2020. His comments had raised fears that politics may be prioritised over safety in the rush to get a COVID vaccine.

According to the World Health Organisation, nearly 180 vaccine candidates are being tested around the world but none have yet completed clinical trials. This excludes Russia's COVID-19 vaccine- Sputnik V, which was officially registered by the Russian Ministry of Health on August 11, becoming the world's first registered vaccine against COVID-19.

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