The head of the U.S. government's Operation Warp Speed COVID-19 vaccine program, Moncef Slaoui, said he expects phase 3 clinical trial data for multiple coronavirus vaccines in the November-to-December timeframe. BNT162b2, the vaccine developed by Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) and mRNA-1273 from Moderna (NASDAQ:MRNA) will be in the first round Slaoui said at a symposium conducted by the Johns Hopkins University and the University of Washington. Data on AstraZeneca's (NYSE:AZN) vaccine from studies in the U.K., Brazil, and South Africa could come in late October to November.

That's a slight delay from the projections the companies have given for the earliest the data could be available. Pfizer and BioNTech have said they could have data as early as the end of this month. And Moderna's management has made reference to having data around Thanksgiving. Of course, depending when in November or December the data appears, the delay could just be a matter of a few days.

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In many clinical trials, the timing of data is known because patients are treated for a certain amount of time and then evaluated to see if the drug worked. But vaccine trials are more like cancer trials. Patients are treated and then researchers have to wait for an event: progression of disease or death for cancer studies, or developing COVID-19 for the coronavirus vaccine studies.

Because the researchers are blinded to which participants get the vaccine and which get the placebo, the trials are set up to be stopped after a certain number of infections have taken place, and then the researchers look at which treatment each infected person received to see if the vaccine worked. The studies have interim looks built into them so the data monitoring committees can stop the studies if it's clear the vaccine works.

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