I think that health epidemics most likely do kill more people then the number that is reported by governments. The reason they go unreported is because it is almost impossible to track the amount of deaths that occur. There may be some deaths that happened some time after the event.
As it's impossible to get a completely accurate number on how many people are killed in a health epidemic, there could be any number of people that have died and gone unreported. As it's in most cases not intentional to report less than what it is, some governments may do it on purpose to not give people fear.
I definitely think that health epidemics kill more people than the government likes to report. I think it only makes sense that the number be reduced a bit to prevent too much panic in the general public when they hear something about a health epidemic in the news or Internet.
Governments have no reason to shade statistics over when a health epidemic hits. If they were to do this, medical doctors and universities would be able to track it and call them out on it. The CDC gives very direct information about all diseases, including epidemics. It is sound information.
It does not benefit the government to publish false or inaccurate reports about how many people were killed in an epidemic. If the government does that then it runs the risk of totally undermining her effectiveness, authority and power.And nothing can be more damaging to a government than all that.