A pair of German twins has reportedly become about $8 billion richer this year thanks to their bet on BioNTech, the upstart firm that has helped Pfizer create its breakthrough COVID-19 shot.

Andreas and Thomas Struengmann helped give BioNTech 150 million euros in seed money in 2008, about three years after they sold their generic drug business for roughly $6.7 billion, Bloomberg News reported.

The 70-year-old brothers have seen their combined fortune balloon to $22 billion this year amid an explosion in BioNTech’s stock price, according to Bloomberg, helped by this week’s announcement that the coronavirus vaccine it’s developed with Pfizer is more than 90 percent effective.

The Struengmanns own about half of the Mainz, Germany-based company, a stake that’s worth $12.2 billion in all, according to Bloomberg’s Billionaires Index. They also hold significant stakes in 4SC and Immatics, two other publicly traded biotech firms, Bloomberg’s data show.

The brothers weren’t always so bullish on biotech. In an interview last year with Germany’s Handelsblatt newspaper, Thomas Struengmann said they initially planned to invest no more than 1 billion euros in industry firms because they take a long time to make progress and sometimes fail.

But they eventually decided to break that limit and went on to invest 1.2 to 1.3 billion euros ($1.4 billion to $1.5 billion) in various biotech outfits, he said.

“There are also initial successes, and then you want to see your little plants continue to grow,” he told Handelsblatt.

BioNTech’s US-listed stock price has roughly tripled this year to close at $101.63 on Thursday. That’s also been a boon to company founders Dr. Ozlem Tureci and Dr. Ugur Sahin, a husband-and-wife team who are now reportedly among the richest couples in Germany.

The Streungmanns apparently have a lot of trust in the pair — they previously backed Ganymed Pharmaceuticals, a cancer-treatment venture that Tureci and Sahin founded in 2001, according to Bloomberg. The brothers see BioNTech as a “long-term investment, Thomas Struengmann told Handelsblatt.

“BioNTech is the company that comes closest to our vision of an innovative pharmaceutical company,” he told the paper.