Pfizer Inc Chief Executive Officer Albert Bourla said on Saturday he had tested positive for Covid-19.
"I'm feeling well and symptom free," Bourla said in a statement.
Bourla, 60, back in August had contacted Covid and had started a course of the company's oral Covid-19 antiviral treatment, Paxlovid.
Paxlovid is an antiviral medication that is used to treat high-risk people, such as older patients.
Bourla has received four doses of the Covid vaccine developed by Pfizer and its German partner BioNTech (22UAy.DE).
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 sub variants, which make up 84.8% and 1.8%, 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 FDA authorised Pfizer and Moderna's updated booster shots that target the dominant BA.4 and BA.5 Omicron sub variants.
A federal health agency said this week that over 25 million doses of the so-called bivalent shots had been sent out. That consisted mostly of the Pfizer/BioNTech vaccine, as production of the Moderna vaccine ramps up.