“[Sinovac’s] Omicron-specific vaccine can stimulate quite strong immune responses and antibody levels in small animals, which is in line with our expectations,” Meng Weining, a vice president at Sinovac, told the South China Morning Post on Thursday. Meng expects final human trials on the vaccine to start within weeks and said data from the trials could be ready by next month.

Sinovac is not the only firm making an Omicron-specific jab. U.S. pharmaceutical giant Pfizer and Britain’s AstraZeneca say they also expect Omicron-specific shots to be ready this spring. But producing the Omicron-specific jab may be more crucial for Sinovac given how much the efficacy of its vaccine has appeared to wane against Omicron.

A study published last month in Nature, a scientific journal, showed that two doses of Sinovac’s vaccine produced no antibodies neutralizing Omicron. In another study from December, researchers in Hong Kong found that three doses of Sinovac’s vaccine failed to produce the antibodies needed to fend off the virus. The three-dose Sinovac regimen also underperformed compared with three doses of BioNTech’s mRNA jab or two doses of Sinovac followed by a BioNTech booster.

Despite studies suggesting that Sinovac provides little to no protection from the Omicron variant, China continues to rely on the jab, as well as a similar inactivated shot from state-owned maker Sinopharm. China is still distributing primary and booster doses of both vaccines instead of turning to more effective foreign-made mRNA jabs. Chinese authorities so far have rejected all foreign-made vaccines, including the mRNA jab from German mRNA vaccine maker BioNTech, which has been proven effective and could be distributed locally via China’s Fosun Pharma.

Experts have warned that China’s reliance on less effective vaccines from Sinovac and Sinopharm, along with the country’s success in containing COVID-19 with tight border restrictions and COVID-zero policies, have created an “immunity gap” in China. The term highlights the lack of natural and vaccine immunity in China’s population compared with places like the U.S. which have experienced large COVID outbreaks and distributed highly effective mRNA shots.

Experts warn that, eventually, China will need to accept mRNA jabs to overcome its immunity gap—even if it does so on its own terms. In late January, the European Chamber of Commerce in Hong Kong said in a report that China likely will not reopen its borders until it rolls out a homegrown mRNA jab to its population as booster shots, Bloomberg reports.

Among homegrown mRNA vaccine makers, Walvax Biotechnology is closest to the finish line.

In late January, Walvax published Phase I clinical data showing that its mRNA vaccine induced an immune response and may become a viable vaccine. Walvax has not said when the jab may be ready for widespread distribution, but it is currently testing the shot on tens of thousands of people in Mexico and Indonesia. But analysts said that Walvax’s Phase I results did not appear to match the efficaciousness of the widely deployed mRNA vaccines from Pfizer and Moderna[/hotlink. Walvax’s jab potentially induced more side effects and was only effective under specific dosing regimens.

“China’s own mRNA vaccine candidates are still far away in their development and of unproven quality,” analysts at the U.S. think tank Center for Strategic and International Studies wrote in a post this week.

Sinovac, meanwhile, has a track record that proves it can quickly produce its vaccine en masse. As of mid-January, Sinovac ranked just ahead of Pfizer and AstraZeneca as the world’s largest vaccine distributor, having sent out nearly 2.5 billion doses of its vaccine since the beginning of the pandemic, according to research firm Airfinity.

Now Sinovac appears confident it can quickly shift its manufacturing might to make an Omicron-specific shot.

“The technology and production is the same [with the ancestral virus], and a vaccine for research can be prepared very quickly after isolation of the strain. Production is not an issue,” Sinovac said in a statement late last year after Omicron first emerged.

If Sinovac’s Omicron-specific jab works, it may be China’s best bet to boost the immunity of its 1.4 billion people and start on a path toward reopening.