Taiwan is banking on a homegrown Covid-19 shot to speed up its inoculation program as the island and many countries struggle to secure vaccine deliveries from major drug companies.

The locally produced Covid vaccine from Medigen Vaccine Biologics was rolled out last week, with President Tsai Ing-wen receiving her first shot of the two-dose vaccine last Monday.

Medigen’s vaccine was developed in collaboration with the National Institutes of Health in the U.S. The vaccine — like the one from Novavax — is based on a technology called recombinant protein, which uses a part of the coronavirus protein to induce an immune response.

In the past week, around 600,000 people in Taiwan were inoculated with the Medigen vaccine, the company’s Chief Executive Charles Chen told CNBC’s “Squawk Box Asia” on Tuesday.

Some critics have questioned the approval of Medigen’s vaccine. Health authorities cleared the vaccine for emergency use in July after completing only phase two clinical trials in Taiwan with no available efficacy data.  

Chen told CNBC that it was not possible to conduct a “traditional efficacy trial” because Taiwan’s infection rate is “so low.” Such a trial typically involves a comparison between a vaccinated group and a control group that does not receive the vaccine, he explained.

Instead, Medigen used a method called “immunobridging” to infer the vaccine’s protection level based on the immune responses in trial participants.   

“We will say that our protection will be … the same or even better than AstraZeneca,” said Chen.

Medigen said in July that it received approval to conduct a phase three clinical trial for its Covid vaccine in Paraguay.

Taiwan’s inoculation program got off to a slow start as it — like many governments globally — faced challenges in securing Covid vaccine deliveries.

The island, with a population of roughly 24 million, has received more than 10 million doses of Moderna and AstraZeneca vaccines, according to public data compiled by Unicef. That includes nearly 6 million doses donated by the U.S. and Japan, the data showed.

Around 42% of Taiwan’s population has received at least one shot of the Covid vaccine, of which fewer than 4% has been fully vaccinated, according to statistics compiled by online repository Our World in Data.  

While Taiwan reported very few Covid infections last year, the island’s cases jumped in May. Still, Taiwan’s cumulative case total remains relatively low. The number of daily reported cases in the island has since dropped, unlike many of its Asian neighbors which are still struggling with surging infections.

The island has reported 15,995 confirmed cases and 835 deaths since the start of last year, the Taiwan Centers for Disease Control said Tuesday.