Adverse event in COVID-19 vaccine trial ‘not related to vaccine’, says Sinovac

By Rachel Arthur

- Last updated on GMT


Related tags Brazil Sinovac COVID-19 vaccine

Sinovac’s Phase 3 COVID-19 vaccine trial has been put on hold in Brazil after a serious adverse event. But in a statement this morning, the company says the event is not related to the vaccine.

Brazil’s Agência Nacional de Vigilância Sanitária (Anvisa) announced yesterday that it had interrupted the clinical studies of the CoronaVac vaccine, after a serious adverse event took place on October 29.

Neither Anvisa nor Sinovac have released the nature of the event; or if the event occurred in a vaccine or placebo group.

A statement from Sinovac today says: After communicating with the Brazilian partner Butantan Institute, we learned the head of Butantan Institute believed that this serious adverse event (SAE) is not related to the vaccine.  Sinovac will continue to communicate with Brazil on this matter.  The clinical study in Brazil is strictly carried out in accordance with GCP requirements and we are confident in the safety of the vaccine.”

Global Phase 3 trials ​for inactivated candidate

China’s Sinovac Biotech is running COVID-19 vaccine Phase 3 trials in Turkey, Indonesia and Brazil.

The randomized, double-blinded and placebo controlled Brazilian study is evaluating the vaccine in healthcare professionals. It is testing the vaccine in two groups: one of healthy adults aged 18-59 years old; and a second group of adults aged over 60.

Sinovac has partnered with Instituto Butantan for the Phase 3 trial in Brazil, with Instituto Butantan being the main producer of immunobiological products and vaccines in the country.

The vaccine is an inactivated, two dose vaccine: with doses administered 14 days apart. 

The company’s Phase I/II clinical trials of CoronaVac in adults (18 to 59 years old) and elderly volunteers (60 years old and above) were conducted in Jiangsu and Hebei Provinces in China earlier this year. From these studies, Sinovac reported that “the vaccine candidate appeared to be well tolerated for different dosage and no serious vaccine-related adverse events were reported, demonstrating a good safety profile for the vaccine candidate. Both seroconversion rates in adults and elderly volunteers were above 90%, indicating favorable immunogenicity of CoronaVac.

Trial on hold for unknown duration

Sinovac's candidate is one of nine COVID-19 vaccines in Phase 3 trials worldwide. Sinovac is not the first COVID-19 vaccine developer to face this kind of hurdle: AstraZeneca ​and Johnson & Johnson​ have also suffered similar setbacks with their Phase 3 vaccine trials. With large numbers of participants involved in Phase 3 trials, companies highlight that adverse events are to be expected in such clinical studies.

However, a clinical pause or hold does create a delay of unknown duration for vaccine developers. In Brazil, Sinovac will have to wait until Anvisa is satisfied that the serious adverse event was not linked to the vaccine candidate in order for trials to be resumed.  

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