(Bloomberg) -- The US shortage of Pfizer Inc.’s drug that’s the optimal treatment for syphilis will likely extend at least into October as the country faces skyrocketing rates of the potentially deadly disease.

While Pfizer had anticipated supplies of Bicillin L-A would normalize by the end of June, the expected shortfall has been extended into the final three months of the year, according to an update of a Food and Drug Administration website Friday. It’s unclear whether Pfizer expects a normal supply toward the beginning or end of the fourth quarter. The company didn’t immediately provide comment.

US rates of syphilis, a sexually transmitted bacterial infection, have been increasing for years amid declining public health funding, increased substance abuse and riskier sexual behavior. The most recent shortage of Bicillin L-A, which began in April last year, makes it even harder for clinicians to treat the disease. A form of penicillin, the drug can cure syphilis with as little as one shot, while alternative treatments require weeks of twice-daily pills.

It’s also the only drug that prevents the disease from passing from a pregnant person to the fetus and causing congenital syphilis. Without treatment, congenital syphilis is deadly: In 2022, it caused 231 stillbirths and 51 infant deaths, according to the Centers for Disease Control and Prevention. 

To expand supply, the FDA allowed importation of about 50,000 doses of another version of the drug, a common move to alleviate shortages. That version is approved outside the US, and not by the FDA. Pfizer has also increased production and shortened Bicillin L-A’s manufacturing time. The US government also stood up a task force last year to address rising rates of syphilis.

Pfizer has said it will consider the situation back to normal when there is “sufficient supply and several weeks of reserves.” The shares rose 1.5% as of 1:16 p.m. Friday after losing 7% this year through Thursday’s close. 

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