NEW YORK — Drugmaker Pfizer said Thursday it is seeing waning immunity from its coronavirus vaccine and says it is picking up its efforts to develop a booster dose that will protect people from variants.

Pfizer said it would soon publish data about a third dose of vaccine and submit it to the US Food and Drug Administration, European Medicines Agency and other regulators. The company specified it would seek FDA emergency use authorization for a booster dose in August.

But in an unusual move, two top federal agencies said Americans don't need boosters yet and said it was not up to companies alone to decide when they might be needed.

Hours after Pfizer issued its statement, the FDA and Centers for Disease and Control issued a joint statement saying Americans do not need booster shots yet.

"Americans who have been fully vaccinated do not need a booster shot at this time," they said.

In a statement to CNN on Friday, the World Health Organization said, "We don't know whether booster vaccines will be needed to maintain protection against COVID-19 until additional data is collected," adding, "limited data available on how long the protection from current doses lasts and whether an additional booster dose would be beneficial and for whom."

Pfizer and its partner BioNTech said evidence was building that people's immunity starts to wane after they have been vaccinated. The Pfizer vaccine requires two doses to provide full immunity.

"As seen in real-world data released from the Israel Ministry of Health, vaccine efficacy in preventing both infection and symptomatic disease has declined six months post-vaccination, although efficacy in preventing serious illnesses remains high," Pfizer said in a statement.

"Additionally, during this period the Delta variant is becoming the dominant variant in Israel as well as many other countries. These findings are consistent with an ongoing analysis from the Companies' Phase 3 study," it added.

"While protection against severe disease remained high across the full six 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 believe that a third dose may be beneficial within 6 to 12 months following the second dose to maintain highest levels of protection."

It gave no further details.

The announcement could have implications across the world. The Pfizer shot is the cornerstone of vaccination programs in many countries. Two-thirds of doses delivered across the European Union were made by Pfizer, according to the European Center. In Israel, Pfizer is the only vaccine used.

Of the 158 million fully vaccinated people in the US, more than half received the Pfizer shot.

US government officials have stressed that fully vaccinated people have a low risk of infection, even from the Delta or B.1.617.2 variant, which is more transmissible than earlier lineages of the virus.

Plus, several studies have indicated the mRNA vaccines made by Pfizer and Moderna confer long-term protection.

"FDA, CDC, and NIH (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," they added.

It was a clear message to Pfizer, which has been hinting at the need for a booster shot for months.

"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," the CDC and FDA said in the statement.

"The United States is fortunate to have highly effective vaccines that are widely available for those aged 12 and up. People who are fully vaccinated are protected from severe disease and death, including from the variants currently circulating in the country such as Delta," the statement continued.

"People who are not vaccinated remain at risk. Virtually all COVID-19 hospitalizations and deaths are among those who are unvaccinated. We encourage Americans who have not yet been vaccinated to get vaccinated as soon as possible to protect themselves and their community."

Israel's health ministry said in a statement earlier this week that it had seen the efficacy of Pfizer's vaccine drop from more than 90 percent to about 64 percent as the B.1.617.2 or Delta variant spread.

Pfizer said research showed booster doses of its vaccine, developed with BioNTech, produced levels of neutralizing antibodies that are five to 10 times higher than what's produced after two doses.

It said it's also developing a new formulation for a booster dose that may more thoroughly protect people from new variants.

"While Pfizer and BioNTech believe 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 are remaining vigilant and are developing an updated version of the Pfizer-BioNTech COVID-19 vaccine that targets the full spike protein of the Delta variant," the company said. Current vaccines target just a piece of the spike protein — the part of the virus it uses to attach to cells.

"The first batch of the mRNA for the trial has already been manufactured at BioNTech's facility in Mainz, Germany. The Companies anticipate the clinical studies to begin in August, subject to regulatory approvals." — CNN