Phase 2 clinical trial results of a COVID-19 vaccine developed by Medigen Vaccine Biologics Corp generated good data, experts said, although they warned that there was still no way to know how effectively it would prevent the disease.
“Data look quite good,” Academia Sinica researcher Michael Lai (賴明詔) said on Thursday after Medigen announced that its vaccine candidate had shown no major safety concerns.
The data showed that the vaccine produced sufficient neutralizing antibodies and as long as there were antibodies, there should be protection, Lai said, adding that its toxicity was low.
Photo: Tsai Wen-chu, Taipei Times
The Medigen vaccine has achieved the goals of creating sufficient neutralizing antibodies and having low toxicity, but only phase 3 trials could determine if it actually protects people who receive it, said Lai, who is a virologist and a coronavirus researcher.
There are many ways to produce vaccines, including via protein subunits such as the one Medigen is working on, he said.
The most traditional way is to use the virus to produce a vaccine with several proteins that the immune system recognizes should not be there, triggering an immune response, he said.
However, this method can produce a level of toxicity, he said.
A protein subunit vaccine has only one protein, in this case a spike protein, he said.
“It is purer, but could trigger a weaker immune reaction,” Lai said. “Different vaccine production methods have different advantages and disadvantages. One cannot be compared to another.”
It could take several years for a domestic vaccine to go through phase 3 trials, so given Taiwan’s situation, “it should opt for second-best,” even though major vaccines made elsewhere in a matter of months obtained enough efficacy data in phase 3 trials to get emergency use authorization (EUA), he said.
It would be acceptable for Medigen to apply for EUA with only the results of its phase 2 trials, he said.
National Taiwan University Hospital pediatrician Lu Chun-yi (呂俊毅), who is secretary-general of the Taiwan Immunization Vision and Strategy organization, said that the Medigen data were “good.”
Almost every participant had antibodies after being inoculated and the antibody concentration data were promising, Lu said.
However, there is no international consensus on how high the geometric mean titer (GMT) — or antibody concentration — has to be to indicate sufficient protection, he said.
Moreover, no uniform, globally accepted method for verifying antibody concentrations exists, meaning that vaccines have a wide range of GMTs, from as low as just over 100 to above 3,000, he said.
Different laboratories conduct trials with different materials and methods, leading to results that vary across labs, Lu said.
Shih Shin-ru (施信如), who heads the Research Center for Emerging Viral Infections at Chang Gung University said that it was still too early to say whether Medigen had successfully developed a COVID-19 vaccine, because nobody knows how high the neutralizing antibody concentration needs to be.
Medigen said it would seek an EUA from the Food and Drug Administration as soon as possible based on the promising results from its phase 2 clinical trials.
It would also apply to the European Medicines Agency and other international health authorities to begin phase 3 clinical trials as soon as possible, it said.
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