Brazil halts Sinovac Covid-19 vaccine trial due to adverse event

PT Jyothi Datta Mumbai | Updated on November 10, 2020

A file photo of a booth displaying a coronavirus vaccine candidate from Sinovac Biotech Ltd is seen at the 2020 China International Fair for Trade in Services (CIFTIS), following the Covid-19 outbreak, in Beijing, on September 4, 2020.   -  REUTERS

Two different incidents over the last two days illustrate the slippery slope that is vaccine development.

Brazilian health authorities have halted late-stage clinical trials on a Covid-19 vaccine candidate from Chinese company Sinovac Biotech, following a adverse event, according to reports on Tuesday.

The setback comes a day after American-major Pfizer was upbeat on its Covid-19 vaccine candidate showing 90 per cent efficacy, in an interim analysis from late-stage trials.


The two incidents, though divergent, are typical of clinical trials to develop a vaccine, say public health experts. The takeaways from these incidents are that good science is being followed when trials are paused to review an adverse event. And, it’s not over till it’s over, until complete details on efficacy and safety are made available, they add.

On Sinovac’s vaccine, a report from Rio De Janeiro saidthe Brazilian regulator Anvisa “ruled to interrupt the clinical trial of the CoronaVac vaccine after a serious adverse incident on October 29”. The incident reportedly involved a death, possibly not linked to the vaccine. More details are expected from Brazilian authorities later on Tuesday.

In its statement, Sinovac said that after communicating with Brazilian partner Butantan Institute, “we learned the head of Butantan Institute believed that this serious adverse event (SAE) is not related to the vaccine”. And while they would continue to communicate with Brazil on the issue, the company said “the clinical study in Brazil is strictly carried out in accordance with GCP (Good Clinical Practices) requirements and we are confident in the safety of the vaccine”.

Pause and review

Previously, the AstraZeneca-Oxford University-combine and Johnson and Johnson had also paused trials following adverse events. Such incidents will continue to be reported as more companies progress with their late-stage trials on Covid-19 vaccine candidates, say experts. The reassuring part is that vaccine trials are paused for review not just in the United Kingdom or America, but in other parts of the world as well, indicating good practices are being followed in different regions, a public health expert pointed out.

But the enthusiasm around Pfizer’s announcement has drawn flak from some quarters. The expert, however, explainsthat the date and benchmarks for a clinical trial are pre-set and the latest information was revealed on achieving those milestones. The challenge with Pfizer’s vaccine will be distribution, requiring storage at – (minus) 80 degrees C, he pointed out. The vaccine also has some distance to go on safety.

Similar results are expected from Moderna’s vaccine, as well.

Political undercurrent

But politics has muddied the waters for Covid-19 vaccines. On the Sinovac vaccine incident, reports saidthe public health centre coordinating these trials in Brazil was surprised by the decision to halt the trial, as it was investigating details. The vaccine is reportedly caught in a political battle, as it was supported by a governor who was opposed to Brazil’s President (who reportedly supports the AZ vaccine). Brazil had not halted the AZ-Oxford vaccine trial earlier, after a death had been reported.

In Pfizer’s case, some government officials are taking credit for the vaccine that they claim to have funded, something the company denies.

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Published on November 10, 2020
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