system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Does the average citizen of the UNSC know of the Flood's existence?

Did survivors of Voi spread the word of the existence of the Flood? Or did ONI run a massive campaign to cover up their existence?
gpt
Because of the nature of the incident, it wouldn't require a massive cover up campaign by ONI to keep the knowledge locked up. By the time the Flood touched down, Voi had been in Covenant hands for nearly a month. Between the obvious evacuation the UNSC would have attempted, the terrible treatment of civilians by the Covenant, and the Flood's need for biomass, there would be few if any potential civilians to spread any news of the Flood. That means the only people encountering the Flood and living to tell the tale would be UNSC military who can obviously be ordered not to tell anyone about the Flood and punished harshly if they do. 

That said, there was almost certainly a cover up. Regardless of whether or not there were civilian survivors, a part of Earth getting glassed is a huge deal. Keep in mind that at the time of the glassing of Voi the Covenant Separatists had been on humanity's side for a little over a month, and after 25 years of war the average civilian would have neither the ability nor the desire to tell the difference between a loyalist and a separatist. Can you imagine the outrage if the general public found out that UNSC leadership had given the go ahead for part of Earth being glassed? The only possible way for anyone involved to not be hounded to their graves by the media and the public would be to announce the involvement of the Flood and hope that the populace sees the threat posed by a race they've never heard of before. From the standpoint of ONI and the UNSC, it's better if the glassing goes down in history as Covenant Loyalists starting the glassing process.