What happened Shares of BioNTech (NASDAQ: BNTX) were trading down by 17.6% as of 11:50 a.m. EDT on Tuesday. The German biotech didn't announce any news that would explain such a decline. Its COVID-19 vaccine partner, Pfizer (NYSE: PFE), even raised its 2021 sales forecast for BNT162b2 to $26 billion. So why did BioNTech's shares slide? The most likely reason is that the mood of the overall stock market is weighing on this biotech stock. Some investors could also be taking profits off the table after BioNTech's big jump Monday on news that BNT162b2 could have an accelerated path to market in India. Image source: Getty Images. So what It's important to remember that even after factoring in BioNTech's Tuesday morning decline, it's still up by more than 110% year to date. Some volatility is to be expected with high-flying stocks. There are more reasons to be optimistic about BioNTech's prospects, though. Pfizer and BioNTech already have sealed deals to supply their COVID-19 vaccine to Canada and Israel beyond 2021. The companies are talking with other countries about similar agreements. Now what BioNTech could give investors a reason to jump back into the stock soon. The company is scheduled to announce its first-quarter results on May 10. Based on Pfizer's Tuesday update, BioNTech should have impressive revenue growth to report. 10 stocks we like better than BioNTech SEWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and BioNTech SE wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of February 24, 2021 Keith Speights owns shares of Pfizer. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source