The supply of the coronavirus vaccine developed by Pfizer (PFE 0.11%) and BioNTech (BNTX 2.23%) will be significantly lower than first anticipated -- at least in the initial stages of distribution. Pfizer said that it will likely ship only half of the doses it originally planned, due to a set of challenges it wasn't able to surmount.

Addressing two of these, an unnamed company spokeswoman, quoted in The Wall Street Journal, said that "Scaling up the raw material supply chain took longer than expected, and it's important to highlight that the outcome of the clinical trial was somewhat later than the initial projection."

Gloved hand filling a syringe from a vial.

Image source: Getty Images.

As a result, around 50 million doses of BNT162b2 will be shipped by the end of this year, down from the initial goal of 100 million. Next year, though, the big pharmaceutical company should be able to mobilize its supply and logistics efforts to distribute over 1 billion doses throughout the world.

BNT162b2 is administered in a two-dose regimen, with the booster shot coming several weeks after the first jab.

News about the supply shortfall comes one day after BNT162b2 received approval for emergency use by the U.K. government. The government said that the vaccine would start to be distributed and administered in the country next week.

BNT162b2, which showed an extremely high efficacy rate of 95% with no serious safety concerns in phase 3 clinical trials, has been submitted for similar approvals throughout the European Union, and with the U.S. Food and Drug Administration (FDA). In the wake of the U.K. approval, Pfizer and BioNTech anticipate decisions from other major regulators this month.

On Thursday, Pfizer's stock price fell harder than the S&P 500 index, declining by 1.7%.