Pfizer’s COVID-19 Vaccine Shows Mild-To-Moderate Side Effects in Phase 3 Clinical Trial

Pfizer Inc. (New York, NY, USA) has stated that participants in an ongoing late-stage study who were given either its experimental COVID-19 vaccine or a placebo were showing mild-to-moderate side effects.

Pfizer is developing the investigational vaccine candidate in partnership with Biopharmaceutical New Technologies (BioNTech Mainz, Germany). The experimental COVID-19 vaccine is based on BioNTech’s proprietary mRNA technology and supported by Pfizer’s global vaccine development and manufacturing capabilities.


Pfizer is conducting a placebo-controlled trial to evaluate the safety and efficacy of the COVID-19 vaccine in up to 44,000 participants who will receive either the vaccine or placebo. During an investor conference call, Pfizer executives confirmed that it had enrolled over 29,000 people for the trial and had given a second dose of the experimental COVID-19 vaccine to more than 12,000 study participants. The COVID-19 vaccine had demonstrated a "mostly mild to moderate” safety profile, with rare instances of severe or grade 4 side effects. According to the company, the study participants who had been given only the first dose of COVID-19 vaccine experienced mainly fatigue and headache, with others reported muscle pain, diarrhea, chills and joint pain.

Pfizer has assured that it continues to scrutinize the safety and tolerability of the vaccine in its study. The company also said that an independent data monitoring committee could recommend halting the study any time, although it had not done so until now.

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