I don't know if a vaccine is a correct description of the effect. It seems more likely it is epigenetic. Still interesting.......
In 2013, Brachman was working in the lab at Columbia University with her colleague Christine Ann Denny, and they were investigating the human anesthetic — and possible anti-depressant — Calypsol’s effect in mice. Part of their method was using mice who’d been stressed to make them exhibit depression-like behavior the Calypsol could mitigate. “So we would give an injection to mice, and then we'd wait a week, and then we'd run another experiment to save money,” Brachman says in her TED talk. They were re-stressing some mice to run another round of Calypsol tests, but it didn’t work: “They looked like they had never been stressed at all, which is impossible,” she recalls. It turns out the mice had been the ones who’d been administered Calypsol a week earlier — it seems it had somehow inoculated them against the effects of stress.
In her TED talks, Brachman notes that accidental discoveries like theirs are hardly unprecedented in science, nor does it diminish the discoverer’s achievement. She quotes Louis Pasteur: “Fortune favors the prepared mind.”
Brachman continues conducting research at Columbia, and she and Denny have founded biotic startup Paravax, a company developing what they’re calling “paravaccines,” vaccine-like prophylactic drugs. She’s also involved in a non-profit that’s investigating the repurposing of generic medications for the same purpose.