Maybe, just maybe, the mom previously had COVID without knowing it, since over 80% of all known cases were asymptomatic, and as such, would've passed along the antibodies BEFORE getting the vaccine. I hardly think 1-2 months would be enough time to develop antibodies for 2 individuals. The mother makes the antibodies for BOTH herself AND the unborn baby. And usually ONLY for simplistic pathogens. A virus isn't a simplistic pathogen. That's why they require immunization. Besides, those antibodies would be passed thru the colostrum and breast milk AFTER birth, and usually takes months. Babies are usually born with NO viral antibodies, hence the first vaccine administrations within the first 3 months of life.