Nick Mark MD(@nickmmark):Every summer the same warning makes the rounds: "don't get sick in July." That's when the newly minted doctors arrive, interns six weeks out of med school, senior residents in roles they've never held, entire teams reshuffled overnight. In the US we call it the "July Effect." In Britain, more luridly, the "killing season." New people make more errors, and more errors must mean more dead patients. Right? The "July Effect" feels true, but like many intuitive facts in medicine, it's a myth. 🧵 1/

2026.07.06 18:11

Every summer the same warning makes the rounds: "don't get sick in July." That's when the newly minted doctors arrive, interns six weeks out of med school, senior residents in roles they've never held, entire teams reshuffled overnight. In the US we call it the "July Effect." In Britain, more luridly, the "killing season." New people make more errors, and more errors must mean more dead patients. Right? The "July Effect" feels true, but like many intuitive facts in medicine, it's a myth. 🧵 1/