The US pharma giant has already produced several hundred thousand jabs in its Belgium plant, the Daily Mail announced.
They will be ready to go if the clinical trials prove successful and authorities worldwide approve the candidate.
Of these 100mln formulations, 40mln are destined to the UK, but Pfizer aims to produce 1.3bn in 2021. Patients need to receive two doses to complete the course.
On Friday, Pfizer‘s chairman and chief executive Albert Bourla wrote an open letter to clarify the development timeline.
The US authorities require companies to provide two months of safety data on half of the trial participants for emergency authorisation, a milestone Pfizer expects to reach in the third week of November.
Assuming positive data from the 44,000-person trial, the candidate will be submitted to the US Food and Drug Administration after the US Presidential Elections on November 3.
Competitor Moderna Inc (NASDAQ:MRNA) previously said it could apply for emergency authorisation for its COVID-19 vaccine candidate in late November.
All other companies working on this kind of formulations are unlikely to complete safety and efficacy studies by the end of this year.
Shares in Pfizer advanced 2% to US$38.70 in premarket trading.