During a flight in 1983, the NASA space shuttle Icarus opened its cargo bay doors for its mission, and inadvertently an alien microbe attached itself to the inside of the ship. After the orbiter landed and returned to Cape Canaveral in Florida, the deadly microbe multiplied rapidly enough to kill millions of people.
Starfleet assigned the USS Enterprise to a time travel mission in 2279 to alter history and prevent the Icarus plague from ever happening. However, during the mission the ship inadvertently ended up in an alternate timeline. It was not known whether the Enterprise succeeded. (TOS comic: "Getting Real")
If the plague had been erased from history, it apparently was done by covert means. No evidence of overtly dramatic changes to the timeline were evident when the Enterprise crew time traveled to 1986. (TOS movie: The Voyage Home)
- Captain Spock found the microbes with sensors six hours prior to Icarus’ launch, so preventing the plaque could have been done by one of several methods. Since history recorded that only one microbe ended up inside Icarus, then once the microbe was inside the orbiter, beam it up. Alternatives were blanketing the region of microbes with phaser fire, or beaming the microbes into a quarantined container aboard the Enterprise, then once out of view of Earth beaming them back into space and destroying them as was done in TOS episode: "The Changeling".
- The Federation Department of Temporal Investigations was founded in 2270, while the time travel mission to prevent the Icarus plague was assigned in 2279. Therefore most likely the mission would have been overseen and researched by DTI. It was not known why this particular event in human history was singled out to be changed via time travel.
- A pandemic in Florida might spread faster than one in other regions of the United States. Florida’s population was about ten million people in 1983, but the state also averaged 7.5 million visitors per month. Each month, 4.5 million of those visitors went to the tourist city of Orlando, which was only 45 miles away from Cape Canaveral. Weekly tourist traffic could easily and quickly have spread the plague outside of Florida to infect the entire southeastern portion of the country. Since history did not reflect that, Florida must have been quarantined fairly quickly.
- The microbe would have had to have been fairly contagious and fast-acting. For comparison, influenza incubates in 1-3 days and then is contagious for 2-3 days.
- How alien microbes ended up above Earth in 1983 was unknown. However, given that they had a known lifespan, which was relatively short, one possibility was that they were drifting in space in an inert state when they were captured by a comet. Comet IRAS-Araki-Alcock (C/1983 H1) passed within 3 million miles of Earth on May 12, 1983, reportedly "closer than any comet since 1770." When the comet approached Earth, heat from the comet's tail might have revived the microbes and expelled them into Earth orbit.
- In 2266, USS Enterprise discovered that an experimental life-prolongation serum resulted in the deaths of the entire adult population on Miri's homeworld. (TOS episode: "Miri")
- In 2268, USS Exeter was found orbiting Omega IV, her crew apparently slaughtered by a virus. (TOS episode: "The Omega Glory")
- In 2270, Leonard McCoy was arrested for suspicion of causing a plague resulting from a mass inoculation program on Dramia II in 2251. (TAS episode: "Albatross")
- In 2153, Florida faced mass tragedy again, this time from a Xindi strike. (ENT episode: "The Expanse")
- Florida’s population was 9,746,324 in 1980 and 12,937,926 in 1990, with average growth making it 10,134,462 in 1983. There were 53.5 million visitors in Orlando in 2011 and 87.3 million visitors to all of Florida in 2011.
- Cape Canaveral's distance from Orlando
- Influenza's behavior
- Comet proximity