If you're basing this on the Lancet letter about indirect deaths, that's an estimate that includes future deaths that could be linked to past events of the war. So "have been" isn't the right tense.

It's also non-peer-reviewed, and based on rather arbitrarily picking a multiplier of 15x from a range of past conflicts' multipliers. One author described the figure as "purely illustrative" in a now-deleted tweet.