This would only comprise death by natural causes, no accidents, suicides, homicides etc.
As Wikipedia says:
A death by natural causes is one that is primarily attributed to an illness or an internal malfunction of the body not directly influenced by external forces. For example, a person dying from complications from influenza (an infection) or a heart attack (an internal body malfunction) or sudden heart failure would be listed as having died from natural causes.
How long would it take until we realise that on the whole world people suddenly stopped dying by natural causes? (Let's say it is caused by some alien medicament that they are secretly testing on us.)
Instead of death, they are living the same as they did before this day came.