What happened

Shares of BioNTech (NASDAQ:BNTX) jumped 10.9% this week as of the market close on Thursday. There were a couple of primary reasons behind the big gain. BioNTech's partner, Pfizer (NYSE:PFE), increased its full-year sales guidance for the companies' COVID-19 vaccine to $33.5 billion from $26 billion. Pfizer and BioNTech also provided a positive update from early testing of a third booster dose of the vaccine.

So what

BioNTech stands to receive half of the extra $7.5 billion in COVID-19 vaccine sales expected by Pfizer this year. This news by itself served as a solid catalyst for the biotech stock. Even better, Pfizer's revised guidance didn't include any of the additional 200 million doses that the U.S. government announced last week that it's buying.

COVID-19 vaccine vial and syringe on top of a stock chart.

Image source: Getty Images.

Investors were also encouraged by the early results from a third booster dose of the Pfizer-BioNTech vaccine. Pfizer Chief Scientific Officer Mikael Dolsten said that the third dose given six months after the second dose increased neutralizing antibodies against the delta variant by more than fivefold in younger individuals and more than 11-fold in older adults. He added that the companies estimate that a third booster dose could potentially increase neutralizing antibody levels by up to 100 times compared to only two doses.

Now what

BioNTech is scheduled to announce its second-quarter results on Aug. 9. The company and Pfizer also expect to file for Emergency Use Authorization of a third booster dose of their COVID-19 vaccine as early as next month.

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