NEW YORK _ Pfizer Inc. and BioNTech will submit data to the Food and Drug Administration in coming weeks supporting a COVID-19 vaccine booster shot.

The companies have seen “encouraging data” in the trial of a third dose of their vaccine, they said Thursday. “Initial data from the study demonstrate that a booster dose given 6 months after the second dose has a consistent tolerability profile while eliciting high neutralization” against the wild type and Beta variant of the coronavirus.

Federal regulators, however, indicated they were wary of approving a booster. “The United States is fortunate to have highly effective vaccines that are widely available for those aged 12 and up,” the FDA and Centers for Disease Control and Prevention said in a joint statement. “People who are fully vaccinated are protected from severe disease and death, including from the variants currently circulating in the country such as Delta. Virtually all COVID-19 hospitalizations and deaths are among those who are unvaccinated. “

“Americans who have been fully vaccinated do not need a booster shot at this time,” the joint statement added. “FDA, CDC, and [the National Institutes of Health] are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary. This process takes into account laboratory data, clinical trial data, and cohort data – which can include data from specific pharmaceutical companies, but does not rely on those data exclusively. We continue to review any new data as it becomes available and will keep the public informed. We are prepared for booster doses if and when the science demonstrates that they are needed.”

Pfizer and BioNTech said while they believe a third dose has “the potential to preserve the highest levels of protective efficacy against all currently known variants including Delta,” they are remaining vigilant and developing an updated  vaccine that targets the full spike protein of the Delta variant. The partners expect clinical studies of the updated version to begin in August.Real world data released by the Israel Ministry of Health has shown vaccine efficacy in preventing both infection and symptomatic disease has declined six months post-vaccination, although efficacy in preventing serious illnesses remains high. And during this period the Delta variant is becoming the dominant variant in Israel as well as many other countries. “That is why we have said, and we continue to believe that it  is likely, based on the totality of the data we have to date, that a third dose may be needed within 6 to 12 months after full vaccination,” the companies said. “While protection against severe disease remained high across the full 6 months, a decline in efficacy against symptomatic disease over time and the continued emergence of variants are expected.”

“Based on the totality of the data they have to date,” Pfizer and BioNTech said they believe “a third dose may be beneficial to maintain the highest levels of protection.”