HONG KONG, BEIJING and CAJICA, Colombia – Anvisa, Brazil’s health care surveillance agency, has halted the final-stage trials for Beijing, China-based Sinovac Biotech Ltd.’s COVID-19 vaccine candidate Coronavac after a serious adverse event occurred on Oct. 29 and was communicated to the regulator. Anvisa then evaluated the data and suspended the trials after weighing the risk-benefit of continuing them in the country, it said.

“We have noted the media reports. After communicating with our Brazilian partner Butantan Institute, we learned the head of Butantan Institute believed that this serious adverse event 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,” Pearson Liu, director of brand management and public relations at Sinovac, told BioWorld.

Anvisa did not comment on reports that the event was linked the death of a trial participant. “Anvisa reiterates that, according to national and international regulations on Good Clinical Practices, data on clinical research volunteers must be kept confidential, in accordance with principles of confidentiality, human dignity and protection of participants,” the agency said.

The suspension comes a mere four months after Anvisa green-lighted the start of phase III trials in Brazil to test Coronavac’s efficacy and safety on July 3. Sinovac subsidiary Sinovac Life Sciences, who is developing the vaccine, partnered with the Butantan Institute, a public research institution based in Sao Paulo, to apply for the approval. The study aims to recruit 9,000 health professionals directly taking care of COVID-19 patients, from the states of São Paulo, Rio Grande do Sul, Minas Gerais and Paraná, in addition to the Federal District, to participate in the study, Anvisa said at the time.

The most recent phase III trials for the vaccine began in Turkey in late September. The case-driven, randomized, double-blinded and placebo-controlled phase III trial will test the vaccine’s efficacy and safety. The first stage will involve 1,300 healthcare workers aged between 18 and 59 years old, who will randomly receive either two doses of vaccine or a placebo at two-week intervals. The second stage will see around 12,000 members of the general population, aged between 18 and 59, receive two doses of the vaccine or placebo at two-week intervals.

PT Bio Farma, Sinovac’s trial partner in Indonesia, has said that its trials are going smoothly.

Upending expectations

Anvisa’s order also comes less than a day after São Paulo Governor João Doria announced the upcoming arrival of the first batch of Coronavac vaccines, expected to arrive in the country on Nov. 20, which will be distributed in the state that he governs. “Studies so far show that Coronavac is the most promising and safest vaccine among vaccines against COVID-19,” he said before Anvisa suspended the trials.

For its part, the Butantan Institute announced in late October that it had received Anvisa’s approval to import raw materials for the formulation and filling of 40 million doses of Coronavac. “This is another important step towards making Coronavac available, which will be applied only after Anvisa's approval and registration as soon as the safety and effectiveness results are proven,” it said.

Anvisa warned that, following its decision, no Brazilians would be allowed to continue receiving shots of Coronavac. “With the study interrupted, no new volunteers can be vaccinated,” it said.

Not alone

Sinovac is hardly alone in facing the suspension of trials for its COVID-19 vaccine. Astrazeneca plc and Oxford University hit pause on all global trials for candidate AZD-1222 in September, due to an unexplained illness in one of the U.K. trials. Since then, Japan’s Pharmaceuticals and Medical Devices Agency approved the resumption of the trials in October, as have other global regulators.

Johnson & Johnson also temporarily paused further dosing of its adenoviral vector-based COVID-19 vaccine candidate JNJ-7843635 in October due to an unexplained illness in a participant from the phase III Ensemble trial. A data safety and monitoring board recommended resuming trial recruitment later that month.

Meanwhile, New York-based Pfizer Inc and Biontech SE hit the headlines for the opposite reason on Monday, giving global stocks a boost as they reported positive interim phase III results from their vaccine candidate BNT-162b2. BNT-162b2 has 90% efficacy in preventing infection, with no serious safety concerns reported so far, according first interim analysis conducted by an independent data monitoring committee. They will continue to gather data from the 43,538-subject phase III trials, the companies said.

The number of COVID-19 cases continues to rise rapidly, with Europe and the U.S. seeing a second wave of cases as winter sets in. There are more than 50.9 million global confirmed cases as of Nov. 10, with more than 5.6 million cases in Brazil alone, according to Johns Hopkins University data.

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