A man receives his third dose of the COVID19 vaccine on July 14, 2021 at Sheba Medical Center in Ramat Gan, Israel.

Amir Levy | Getty Images

Israeli health officials plan to offer booster shots of the Pfizer-BioNTech Covid-19 vaccine to people over the age of 60 as the vaccine’s effectiveness appears to be waning as the Delta variant spreads around the world, NBC News confirmed Thursday.

The heads of the health organizations that have given the Pfizer vaccine will begin giving third vaccinations on Sunday, according to NBC News. The booster vaccination is available to patients over the age of 60 who have received their second vaccination at least five months earlier.

The country’s health ministry reported last week that the two-dose vaccine is now only 39% effective in Israel, where the highly transmissible Delta variant is the dominant strain. The syringe still works very well at preventing people from getting seriously ill, Israeli officials said, showing 88% effectiveness against hospital stays and 91% effectiveness against serious illnesses.

The data from Israel, which began vaccinating its population before many other countries, supports drug manufacturers’ arguments that people will eventually need a booster vaccination to protect themselves from new variants.

Pfizer CEO Albert Bourla on Wednesday doubled his remarks that people will need a third dose of the vaccine to maintain high levels of protection against the virus. The US drug maker released new data Wednesday from a company-funded study that showed the vaccine’s effectiveness dropped to about 84% after four to six months.

“We have also seen data from Israel that immunity is declining and that affects what used to be 100% against hospitalization,” Bourla said on CNBC’s The Exchange.

The Centers for Disease Control and Prevention, the Food and Drug Administration and the World Health Organization have stated that they are not currently recommending a Covid booster due to a lack of data. US and global health officials have said they are looking at Israeli research, which has not been peer-reviewed and has given little detail.

“We need to be aware that these vaccines can become less effective over time,” said Dr. Isaac Bogoch, professor of infectious diseases at the University of Toronto, in a recent interview.

He stressed that the vaccinations still appear to be highly effective in preventing serious infections and helping hospital systems not get overwhelmed in the colder months. “We are still in the Covid era and anything can happen,” he said.

“We have to be prepared and we have to be agile that at some point people will need a booster,” he added. ‚ÄúThis close monitoring, which is taking place in places like Israel, the UK and other parts of the world, will be very helpful in moving policy forward when and when we need boosters.

Israel’s plans to increase its population come two days after the CDC reversed course and advised fully vaccinated Americans living in areas with high rates of Covid infection to return to wearing face masks indoors. According to a CNBC analysis, the guidelines cover about two-thirds of the US population.

While the Delta variant hits unvaccinated people the hardest, some vaccinated people could carry higher amounts of the virus than previously thought and potentially pass it on to others, said CDC Director Dr. Rochelle Walensky on Tuesday.

Walensky added new data showing that the variant behaves “uniquely different from previous strains of the virus,” suggesting that some people infected with the Delta variant “can be contagious and can transmit the virus to others.”

“This pandemic continues to pose a serious threat to the health of all Americans,” Walensky told reporters on a call. “Today we have new science on the Delta variant that requires us to update the guidelines on what to do when you are fully vaccinated.”

– CNBC’s Kevin Stankiewicz contributed to this report.