The Pfizer vaccine involves two shots taken three weeks apart. Casanova says the first shot, which is merely an introduction that allows the body to get used to the messenger so the immune system can start developing antibodies, had nearly no impact. He said there was some soreness where the injection happened, but other than that, he thought he had received the placebo; he had no symptoms.
Three weeks later, when he received the second shot, he was sure that it was the vaccine. The second shot is a booster, which allows the immune system to kick into action, creating antibodies. The response was noticeable but didn’t last long. He experienced flu-like symptoms, with some chills as he went to bed. By 3 a.m., the symptoms were gone.