Trama

Lois decides not to vaccinate Stewie to "save" him from autism, causing Stewie to run away, and cause the town to have an outbreak.

When a bat gets into the house, Peter's efforts to get rid of it result in Stewie being injured. At the hospital, he is offered his vaccinations and Lois balks when reading about the potential side effects. After reading more negative comments online, she digs in her heels to not vaccinate Stewie and gets Peter to go along with her despite Brian's advice otherwise.

They host an anti-vaccination rally as Brian tries to reach Stewie with his advice, but find themselves alone in their campaign. As Stewie tries to protect himself from germs after Brian's advice, Peter's efforts have caused a spike in parents refusing to vaccinate their kids. At Stewie's daycare, the entire class has come down with measles and the entire town is put in quarantine.

As Brian gloats over being right, Lois has a change of heart and decides she wants to get Stewie vaccinated, but Peter has destroyed all of town's vaccines. When Peter suddenly starts to feel ill, panic sets in as they try to keep Stewie disease free. When he pretends Rupert has become ill, he flees the house. As Lois panics over Stewie's disappearance, he runs into himself from the future who tells him he needs to get out of town, but is really is there to steal glue from him to get high. Trying to cross a bridge by swinging underneath to avoid the police, an upside-down train causes him to release his grip and he is rescued by Sean Penn. Lois is lukewarm to his appearance due to his liberal Hollywood leanings, but he has brought vaccinations for the town.

As the family counts their blessings, they reveal that around 150 people died as the bat returns to get in a final word against Peter.