The 2020 Reuters Institute Digital News report found the use of Instagram for news had doubled since 2018.
The trend is strongest among young people. It said nearly a quarter of UK 18-24-year-olds used Instagram as a source of news about coronavirus.
But social media platforms were also among the least-trusted sources.
Just 26% of people said they trusted social media as a source of information about the virus. A similar percentage said they trusted news that had been shared via chat apps such as Facebook Messenger and WhatsApp.
National governments and news organisations, by contrast, were both trusted by about 59% of respondents.
Instagram is now used by more than a third of all people who answered the survey, and two-thirds of under-25s. And 11% use it for news, putting it just one point behind Twitter.
"Instagram's become very popular with younger people", said Nic Newman, lead author of the report. "They really respond well to stories that are told simply and well with visual images".
Stand-out visual stories in recent months have helped - climate change, the Black Lives Matter movement, and the coronavirus have all seen massive engagement on the platform.