Pfizer (NYSE:PFE) and its partner BioNTech (NSDQ:BNTX) have found that two 3-µg doses of their BNT162b2 (Comirnaty) vaccine were safe but generated an underwhelming immune response in children aged two to five years old.
PFE shares fell 2.45% to $59.75 in early afternoon trading.
The news could delay vaccine availability for younger children.
As a result, the companies plan on amending a clinical trial to test a third dose of the vaccine at least two months after the second dose.
Pfizer notes that the Phase 1/2/3 study is ongoing and is still blinded.
Pfizer noted that similar clinical data in older age demographics showed higher efficacy with two doses — albeit at higher doses.
On a positive note, a third dose of the vaccine was well tolerated in the trial involving two to five-year-olds.
The companies plan on filing for emergency use authorization in children aged 6 months to under 5 years if the third dose is efficacious.
Pfizer and BioNTech will test a third 10-µg dose in trial participants between the ages of 5 and 12.
The Comirnaty vaccine initially offered 90.7% efficacy in children between the ages of 5 to 11 in a Phase 2/3 trial.
The two companies are also conducting clinical research on vaccines specifically for Delta and Beta variants of SARS-CoV-2. In addition, they are also developing an Omicron-specific version of the vaccine.
Pfizer notes that its oral antiviral candidate Paxlovid promises to avoid treatment resistance to SARS-CoV-2 mutation.