A huge change from the game to the show is the audience discovering how Ellie gained her immunity. And … I have questions!
The beginning of the episode showed Anna giving birth to Ellie as she fought off a clicker. The clicker bit Anna as she was pushing Ellie out. Ellie is still connected to Anna via her umbilical cord for a few moments after birth. The show is implying that the clicker’s bite to Anna somehow provided enough infection to Anna’s bloodstream to introduce Cordyceps to Ellie, but not enough to infect her, thus giving her immunity.
But this raises questions about how quickly the CBI infects people. As someone who has given birth, let me educate you: fetuses get their nutrition and blood supply via the placenta, which takes what it needs from the pregnant person’s bloodstream via the uterine wall. It takes some time for whatever the person consumes to get to the fetus — take, for example, a vaccine. It takes about two weeks on average for a vaccine to provide any carryover immunity to a fetus.
Yet, if Ellie gained immunity from this bite at the exact moment of her exiting her mother’s womb, the infection would have had to travel through Anna’s bloodstream instantaneously. But if the infection hit the bloodstream that quickly, why didn’t it also affect Anna just as quickly? If Cordyceps can travel through the bloodstream so rapidly, why don’t people turn minutes after exposure? Do you mean to tell me no other birthing people were bitten mid-labor to become immune like Ellie in 20 years?
Perhaps Cordyceps is like COVID in that it affects every person (and every body) differently. Some people show symptoms, some don’t. Some people get a severe illness, others mild. Is Cordyceps a crapshoot that Anna and Ellie got lucky with?