What happened

BioNTech (BNTX 0.74%), which shot to fame as the co-developer of the BNT162b2 vaccine with Pfizer (PFE 2.40%), well outpaced the 1% gain of the S&P 500 index on Thursday, closing the trading session nearly 5% higher. One big piece of news about its COVID-19 vaccine was particularly encouraging.

So what

The driver of Thursday's share price move was an announcement from BioNTech, Pfizer, and Israel's Ministry of Health drawing on data from the country's vaccination program. According to a comprehensive study, BNT162b2's "effectiveness was at least 97% in preventing symptomatic disease, severe/critical disease and death."

Gloved hand filling a syringe from a vial.

Image source: Getty Images.

Crucially, during the seven weeks for which the data was being collected (Jan. 17 to March 6), BNT162b2 was the only vaccine authorized for use in Israel, and the so-called U.K. variant was the dominant strain of the coronavirus there. Health officials have expressed concern about that variant, as it appears to be significantly more transmissible than the original strain.

There was further good news on the asymptomatic infection front. The analysis conducted by the two companies and the Health Ministry found that BNT162b2 was 94% effective at preventing such infections.

"This clearly demonstrates the power of the COVID-19 vaccine to fight this virus and encourages us to continue even more intensively with our vaccination campaign," said Dr. Yeheskel Levy, director of the Ministry of Health.

Now what

These findings are excellent for the vaccine's makers, although curiously, Pfizer shares actually dipped Thursday. The difference might be that the near-term fortunes of BioNTech, a relatively small biotech, are far more dependent on BNT162b2 than are those of its giant partner.