1. Natural immunity from prev infected individuals could also be passed..studies based in israel and nyc have shown natural immunity is as good or better than vaccination for covid protection against fuethwr infection.
2. Antibody blood tests could see if children in households where parents had antibodies from vaccination or prev infection...had somehow passed antibodies to cbildren.
3. Passing antibodies may not be only aerosol they could be from sharing utensils cups and food in households
4. Schools daycares where one of prime spreaders of covid. Thats how i got covid and omnicron both...never went outside during lockdown...washed off all delivered no contact groceries even washed the outside of loaf bread bags...and as soon as lockdown over guess what positive...key was child passing to us from school...