1. Infected animals in China
2. Weaponized in a lab. Bio-terrorism. Covid-19 seems to be targeting certain people or searching for individuals with specific DNA. If weaponized there should be a cure ... or not.
3. Mutated from another virus. Everything in the simulation evolves (mutates) or goes extinct including the human experiment. Covid 19 will mutate - called variants
4. Something buried under the melting icecaps, permafrost, or oceans now coming to the surface and becoming airborne
Scientists Revive 48,500-Year-Old Virus, Setting World Record. As temperatures rise because of climate change, melting permafrost could cause dormant diseases to re-emerge, researchers warn Smithsonian - December 2, 2022
Rapidly Melting Glaciers Are Releasing a Staggering Payload of Unknown Bacteria Science Alert - November 25, 2022
Scientists Revived Ancient 'Zombie Viruses' Frozen For Eons in Siberia Science Alert - November 24, 2022
Extinct Pathogens Along With Climate Change Ushered The Fall of Ancient Civilizations Science Alert - August 6, 2022
Never-before-seen microbes locked in glacier ice could spark a wave of new pandemics if released Live Science - July 1, 2022
Thousands of new viruses - more than 5,000 - were discovered in the ocean Live Science - April 13, 2022
Over 5,000 Previously Unknown Viruses Have Been Discovered Lurking in The Oceans Science Alert - April 8, 2022
Missing Antarctic microbes raise thorny questions about the search for aliens Science News - July 23, 2021
'Cyborg Soil' Unearths a Complex Web of Hidden Microbial Cities Science Alert - July 24, 2021
Ancient 15,000-Year-Old Viruses Identified in Melting Tibetan Glaciers Science Alert - July 21, 2021
Microbes that feast on crushed rocks thrive in Antarctica's ice-covered lakes Live Science - July 6, 2021
These Tiny Creatures Were Revived After 24,000 Years Frozen in The Siberian Permafrost Science Alert - June 7, 2021
These Bizarre Underground Microbes Haven't Evolved For 175 Million Years Science Alert - April 10, 2021
Lakes isolated beneath Antarctic ice could be more amenable to life than thought PhysOrg - February 17, 2021
Russian scientists probe prehistoric viruses dug from permafrost Raw Story - February 16, 2021
Hidden Beneath a Half Mile of Ice, Antarctic Lake Teems with Life PhysOrg - January 15, 2019
5. Something from outer space on a meteor, asteroid, or space debris - that became airborne.
Alien organisms could hitch a ride on our spacecraft and contaminate Earth, scientists warn Live Science - November 24, 2021
More than 5,000 tons of extraterrestrial dust fall to Earth each year Science Daily - April 8, 2021
Microbes Unknown to Science Discovered on The International Space Station Science Alert - March 16, 2021
'Fireball' meteorite that crashed in Michigan holds extraterrestrial organic compounds. Live Science - January 16, 2018
Earth's atmosphere is full of microbes. Could they help us find life on other worlds? Space.com - January 3, 2021
Theory of Panspermia - the Seeds of Life came from Space
6. Alien plot to eradicate certain bloodlines or all sentient life forms