Pfizer Chief Executive Officer Albert Bourla revealed on Saturday that he tested positive for COVID-19 again, although he had received four doses of the COVID-19 vaccine developed by his company and its German partner BioNTech. 

"I'm feeling well and symptom-free," Bourla said in a statement.

Bourla, 60, was first infected in August, and had started a course of the company's oral COVID-19 antiviral treatment, Paxlovid, which is an antiviral medication that is used to treat high-risk people, such as older patients.

The chief executive said he has not yet taken the new bivalent booster.

Developed by Moderna and the team of Pfizer and BioNTech, the new so-called bivalent shots aim to tackle the BA.5 and BA.4 Omicron subvariants, which make up 84.8 percent and 1.8 percent, respectively, of all circulating variants in the United States, based on latest data.

"I've not had the new bivalent booster yet, as I was following CDC guidelines to wait three months since my previous COVID case which was back in mid-August," Bourla added.

In August, the Food and Drug Administration authorized Pfizer and Moderna's updated booster shots that target the dominant BA.4 and BA.5 Omicron subvariants.

A federal health agency said this week that over 25 million doses of the so-called bivalent shots had been sent out. That consisted of mostly the Pfizer/BioNTech vaccine, as production of the Moderna vaccine ramps up.  

(With input from Reuters)