Taipei, June 11 (CNA) Taiwan's alternative approach to evaluating the efficacy of its COVID-19 vaccine candidates has not been used by any other country in the world as the basis for granting Emergency Use Authorization (EUA), Health Minister Chen Shih-chung (陳時中) acknowledged on Friday.
While Taiwan's vaccine candidates have carried out Phase 1 and Phase 2 clinical trials, none of them have begun larger Phase 3 trials - which are typically the standard for determining efficacy.
However, Taiwan's Food and Drug Administration (FDA) guidelines allow EUAs to be issued without Phase 3 trials being conducted, by simply analyzing Phase 2 results via immunobridging, an approach which uses the immune responses measured in clinical trial participants to infer the overall level of protection the vaccine provides.
Critics, however, argued that this approach, which is based on the potency levels of neutralizing antibodies found in clinical trial participants, cannot be used to accurately determine vaccine efficacy.
During a legislative hearing, Taiwan People's Party Legislator Kao Hung-an (高虹安) asked Minister Chen about review standards for EUA of domestic COVID-19 vaccines, which the FDA published on Thursday.
Kao asked Chen whether Taiwan would be the first country in the world to grant an EUA using immunobridging as a substitute for efficacy data obtained in Phase 3 clinical trials.
Initially, Chen said he could not speak to the approaches being adopted by other countries' regulators, but he argued that immunobridging has been a topic of much discussion in the World Health Organization (WHO).
When pressed further, Chen acknowledged that "there are currently no approvals of this type."
"If that is the case," Kao replied, "then this is genuinely frightening. Taiwan has purchased 10 million (local) vaccines, equivalent to five million people."
"If the efficacy of the domestic vaccines does not meet expectations, then these people are like the emperor without clothes - completely without protection," she said.
Russia and China have also approved COVID-19 vaccines for use before they have entered Phase 3 trials or published efficacy data from Phase 3 trials, but according to Chen, Taiwan would be the first country to grant an EUA using the immunobridging approach.
Debate on the FDA's standards has become more urgent, following Medigen Vaccine Biologics Corp.'s announcement on Thursday that it would soon apply for an EUA, after becoming the first local vaccine maker to unblind results of its Phase 2 clinical trials.
According to Chen, the FDA's EUA review will compare the neutralizing antibody potency levels of Medigen trial participants with those from a control group of 200 recipients of the AstraZeneca (AZ) vaccine in Taiwan.
As data from the AZ group is still pending, the EUA review will likely begin in late June, Chen said, adding that there will be no pressure and no deadline for when it should be completed.
In a follow-up question, Kao noted that the United States FDA had publicly broadcast its EUA review meetings for the Moderna COVID-19 vaccine, and asked Chen if Taiwan's FDA would be willing to do the same.
In response, Chen pledged to respect whatever decision the FDA's vaccine review committee made on the issue, but said there are currently no plans to do so.
At the hearing, Chen expressed a high degree of confidence in the Medigen vaccine, saying it had been shown to be safe, and that the data which will be used to calculate its efficacy looked promising, though the final decision on its approval will be left to the review committee.
Previously, Chen had argued that the numbers of participants the Taiwanese vaccine candidates were tested on in Phase 1 and Phase 2 trials were more than those used in those stages of trials for the internationally-used vaccines such as AZ, Moderna and Pfizer-BioNTech, but experts have pointed out those vaccine makers had used a lot more participants in Phase 3 trials.
If Medigen's vaccine is granted an EUA, and if plans to use immunobridging (in planned Phase 3 trials to be conducted later) gain traction internationally, the vaccine would have a chance of being approved by the WHO, Chen said.
Even without international recognition, Taiwanese people would not be prohibited from entering other countries based on what vaccine they receive, although quarantine procedures may differ slightly, he added.