"As seen in real-world data published by the Israeli Ministry of Health, the vaccine's efficacy in preventing both infection and symptomatic disease has declined six months after vaccination, although efficacy in preventing severe disease remains high," the company said in a statement emailed to CNN.
"In addition, during this period the Delta variant is becoming the dominant variant in Israel, as well as in many other countries. These findings are consistent with an ongoing analysis of the companies' Phase 3 study," it added.
Pfizer CEO: Third COVID-19 Vaccine Dose Likely Within 12 Months
"Although protection against severe disease remained high for the full six months, a decline in efficacy against symptomatic disease is expected over time and the continued emergence of variants. Based on the totality of data to date, Pfizer and BioNTech believe that a third dose may be beneficial between 6 and 12 months following the second dose to maintain the highest levels of protection."
Israel's Health Ministry said in a statement earlier this week that it had found that the efficacy of Pfizer's vaccine had dropped from more than 90% to about 64% as the delta or B.1.617.2 variant spread.
The company said booster doses of its vaccine, developed with BioNTech, produce levels of neutralizing antibodies that are five to 10 times higher than those produced after two doses.
"The companies expect to publish more definitive data soon, as well as in a peer-reviewed journal, and plan to submit the data to the FDA, EMA and other regulatory authorities in the coming weeks," Pfizer said in a statement.
Pfizer also notes that it is developing a new formulation for a booster dose that may further protect people from the new variants.
"While Pfizer and BioNTech believe that a third dose of BNT162b2 has the potential to preserve the highest levels of protective efficacy against all currently known variants, including Delta, the companies remain vigilant and are developing an updated version of the Pfizer-BioNTech COVID-19 vaccine targeting the full Delta variant protein," the company said. Current vaccines target part of the spike protein, the part of the virus that it uses to attach to cells.
"The first batch of mRNA for the trial has already been manufactured at BioNTech's facility in Mainz, Germany. The companies anticipate that clinical studies will begin in August, subject to regulatory approvals."
A Pfizer spokesperson told CNN that the company plans to seek emergency use approval of the booster dose from the FDA in August.