Pharmaceutical giants Pfizer and BioNTech announced there is still some work to be done before they can confidently release the two-dose vaccine for young children. Reassuring that “no safety concerns were identified”, they need to modify their clinical trial for their coronavirus vaccine in young children, “after a two-dose regimen did not produce a sufficient immune response in children ages 2, 3, and 4” reports National Review.

Participants in the trial ages 2-4 will be given yet a third dose of the vaccine two months after they received their second dose. Reportedly participants ages six months to 24 months did see a sufficient immune response from the vaccine.

The coronavirus developed jointly by Pfizer with BioNTech is currently the only COVID-19 vaccine authorized in the U.S. for children ages 5 and up. Moderna and Johnson & Johnson vaccines are only authorized for Americans ages 18 years and older.

Pfizer spokeswoman Jerica Pitts said the companies will not increase the dosage for children but will see if the third dose results in insufficient immunity. The young participants were given one-tenth of the dose potency as the dose given to adults over age 18.

Kathrin Jansen, head of vaccine development at Pfizer, told investors in a call reported by the Washington Post “it is important to note that this adjustment is not anticipated to meaningfully change our expectations that we would file for emergency use authorization and conditional approvals in the second quarter of 2022.”