Drugmaker Pfizer, one of the leaders in the race to develop a COVID-19 vaccine, is tweaking its timeline for when it will know if its experimental two-dose vaccine works.

Pfizer executives had expected data from their 44,000-person international study would show by Oct. 31 how well it prevents coronavirus infections. But on a conference call Tuesday to discuss the company's third-quarter results, Chief Executive Albert Bourla said the answer may not come until next week.

Bourla said the independent committee monitoring its final-stage human study still hasn’t done the first interim analysis of data because the study hasn't reached the predetermined point for that analysis — when 32 of the study volunteers, who've received either Pfizer's vaccine or a dummy shot, become infected. He added that the monitoring committee has not yet unblinded the data to reveal which of the infected participants got the vaccine versus the placebo.

Analysts peppered Bourla and other Pfizer executives with so many questions about the study that he repeatedly asked for their patience.

"We all have our fingers crossed all have our fingers crossed," he said.

Pfizer said the final-stage trial has now enrolled nearly all of the planned participants. Nearly 36,000 had received their second shot as of Monday. The company could seek approval for emergency use from U.S. regulators in late November.

Bourla said Pfizer still estimates it will have safety data from a two-month follow up on the first 22,000 patients in the third week of November, and will have manufacturing quality data before that. Pfizer can apply shortly after that for emergency use authorization from the U.S. Food and Drug Administration.

In an interview, Bourla said he doesn't know whether Pfizer will be the first company to get that authorization. Rival Moderna appears to be running neck and neck with Pfizer.

If it gets emergency use approval this year, Pfizer might have enough vaccine for about 15 million people. It's made hundreds of thousands of doses so far, banking on the vaccine being approved.

UBS analyst Navin Jacob, in a note to investors, speculated the apparent data delay could be due to a slow infection rate or very high vaccine efficacy. He wrote that several drugs brought in lower sales than expected, but called the quarter’s result “fine.”

Pfizer reported its third-quarter profit plunged 71%, mainly due to an $8.1 billion gain a year earlier from giving its consumer health care business to a GlaxoSmithKline joint venture. Pfizer will own 32% of that.

The New York-based company on Tuesday said disruptions from the coronavirus pandemic reduced medicine sales in the U.S. and China by about $500 million. Still, Pfizer managed to top Wall Street expectations, and it raised and narrowed its profit forecasts slightly for all of 2020.

The maker of the world’s top-selling vaccine, Prevnar 13 for preventing pneumonia and related bacterial diseases, reported net income of $2.2 billion, or 39 cents per share, down from $7.7 billion, or $1.36 per share, in 2019’s third quarter.

Excluding one-time items, adjusted income came to $4.1 billion, or 72 cents per share. That beat Wall Street expectations by 2 cents, according to a survey by Zacks Investment Research.

Revenue totaled $12.1 billion, down 4% from $12.7 billion in the year-ago quarter.

Pfizer said it now expects 2020 adjusted earnings per-share of $2.88 to $2.93, tweaked from its July forecast of $2.85 to $2.95. It expects revenue of $48.8 billion to $49.5 billion, narrowed from its previous forecast of $48.6 billion to $50.6 billion.

Chief Financial Officer Frank D'Amelio noted the forecast includes costs of research on COVID-19 but not any medicine sales. He noted that Pfizer has “lots of firepower” and will continue to invest in acquisitions.

Separately, competitor Novavax announced Tuesday that its long-awaited 30,000-person vaccine study in the U.S. is expected to start by the end of November, a few weeks’ delay. Novavax already has enrolled a third of 15,000 planned participants in a similar test in Britain.

The biggest U.S. drugmaker by revenue, Pfizer is in the process of spinning off its established products business, which sells mostly off-patent medicines, to combine it with generic drug maker Mylan, creating a new generic drug giant called Viatris. Pfizer will receive about $12 billion in return and its shareholders will get roughly one Viatris share for each Pfizer share they own.

That deal is expected to close by year-end, leaving Pfizer roughly 20% smaller, nimbler and more focused on developing innovative medicines. Pfizer expects to be able to grow revenue at least 6% annually through 2025 as a result of the transformation.

Pfizer shares rose 10 cents to $38.02 in afternoon trading.

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Follow Linda A. Johnson at https://twitter.com/LindaJ_onPharma