By Brian Stelter, CNN Business

(CNN) -- The vice presidential debate between Mike Pence and Kamala Harris was a much bigger audience draw than the comparable VP debate in 2016, according to preliminary Nielsen ratings.

More than 50 million people watched Tuesday's VP debate across the seven biggest channels on television. About 35 million people watched the 2016 debate between Pence and Tim Kaine on the same seven channels.

The total TV audience for the Pence-Harris debate will increase when Nielsen releases finalized data later in the day on Thursday.

But the substantial increase from 2016 immediately stood out when the initial Nielsen numbers were shared with the networks.

Notably, the Tuesday night face-off is not on track to break the VP debate ratings record that was set in 2008. That year, there was heightened interest in the vice presidential debate between Sarah Palin and Joe Biden.

Nielsen's preliminary data does not include people who watched on TV out of the home; who streamed the debate on phones and other devices; or who listened on the radio.