|This article is about the in-universe outbreak day. For the the real-world annual event, see Outbreak Day (event).|
Though the infection had been rising in intensity for days, it reached such a state when people began to be admitted to hospitals. The infection spread quickly in cities like Austin, eventually being confirmed to have spread nationwide.
A state of national emergency was declared. The Army and the National Guard were mobilized quickly in the early hours of the morning, blocking the highway, setting up a base for residents to flee to for refuge. News networks tried to inform people of this safe area, but many went off the air shortly after the start of the outbreak. Outside Austin, several infected patients escaped from the nearby hospital and attacked people trapped on the highway due to the high amount of traffic.
Much of the city erupted into chaos due to the outbreak. Police cars rushed to various areas in the city, setting up roadblocks to contain citizens believed to be infected, only to be overrun by them. Buildings were set ablaze, some even exploding due to gas leaks despite the Army's efforts to intervene.
The outside country areas of the city were much more quiet. Joel and Sarah's area only appeared to have one Infected, Jimmy Cooper. Many residents in these areas fled towards the city due to the advice on the radio and television, unaware of the chaotic events occurring.
Joel would later look back on that day and how "families were torn apart" and how it was "a God-awful mess."
- A tweet by Naughty Dog developer Mark Richard Davies places Joel's birthday on Outbreak Day. This is backed by the events of the prologue and by in-game newspapers and calendars.
- Naughty Dog celebrates Outbreak Day every year by releasing new content and merchandise such as free PSN avatars and limited-edition posters.
- To commemorate the very first Outbreak Day in 2013, Naughty Dog released behind-the-scenes footage of the musical "alternate ending" to the public.
- On September 24th, 2019, 2 days before Outbreak Day, the initial release date for The Last of Us Part II was announced and preorders were opened for the various special editions of the game in anticipation of a press event on Outbreak Day proper.
- The press event featured the first public, hands-on gameplay demo for Part II.