Hong Kong/Tokyo CNN Business  — 

Japanese tech conglomerate SoftBank just conducted voluntary Covid-19 antibody tests on more than 44,000 employees, their families, clients and outside medical professionals such as doctors and dentists. The company says it is the largest such test by a Japanese company.

To combat another possible wave of cases,”various tests are needed to ensure the safety of our employees and society, so that we can find an exit strategy as quickly as possible,” said SoftBank founder and CEO Masayoshi Son during a live streaming event on Tuesday. He cautioned that a vaccine for the virus might not be able to be mass produced until “the middle of next year.”

SoftBank (SFTBY) on Tuesday said that of the 44,066 people it tested for Covid-19 antibodies, 191 tested positive. Among SoftBank (SFTBY) staff, just 0.04% of employees working at SoftBank (SFTBY)’s mobile carrier retail stores tested positive, a number Son said was surprising. The rate of positive tests among workers people at the Japanese firm’s office and call centers was slightly higher, though not by much: about 0.2% and 0.4%, respectively.

SoftBank used Innovita and Orient Gene test kits, which were developed in China.

Son said he decided to use antibody tests because they can be done safely, widely and quickly. But some experts caution that there are still too many unknowns about the accuracy of antibody tests that are available, and about the nature of the virus itself.

There are dozens of such tests being used or developed in the United States right now, for example, but few are highly accurate. That means they can fail to detect an active virus, thus delivering a false sense of security.

In China, one study of diagnostic tests found the number of false negatives delivered was nearly 40%.

Other experts have warned that the reliance on antibody tests could create new problems, including discrimination in workplaces, or people deliberately trying to get infected so they can return to their jobs sooner. One doctor told CNN that the latter concern was equivalent to “playing Russian roulette.”

Still, other Japanese companies have said they will offer antibody testing as they reopen. Rizap, a gym operator, said it would offer 6,500 free tests to employees, trainers and gym members. And Suntory (STBFY) CEO Takeshi Niinami told CNN that more antibody testing is needed to reassure people that it’s safe to resume business.

Son, meanwhile, has been worried about the coronavirus pandemic for months. The Japanese billionaire ended a yearslong silence on Twitter in early March with a post saying: “It’s been a while since I tweeted. I am worried about the situation of the new coronavirus.”

By then, the pandemic was already wreaking havoc on Son’s business. The collapse in travel and the lockdown restrictions around the world was catastrophic for many of the startups he backed through his $100 billion Vision Fund. The fund suffered operating losses of nearly $18 billion for the fiscal year ended in March, dragging SoftBank to its worst annual loss ever.

The pandemic has also hit Japan’s economy hard, as the country went into lockdown to prevent the spread of the disease. The Japanese government has rolled out a stimulus package worth some 234 trillion yen ($2.2 trillion) — a staggering amount equivalent to almost 40% of the annual output of the world’s third biggest economy.