FYI, it's normal for people living together to not infect each other even without vaccines. SAR has only ever been in the range of 10%-20% ish. Also vaccines haven't managed to alter that.[1] When my girlfriend got COVID (pre-vaccines) she was unable to infect me despite that we were quarantined together for 10 days in close contact, made no effect to reduce contact and she was even cooking for me whilst coughing over the food.

[1] "In the UK it was described that secondary attack rates among household contacts exposed to fully vaccinated index cases was similar to household contacts exposed to unvaccinated index cases (25% for vaccinated vs 23% for unvaccinated)"

https://www.thelancet.com/journals/lanepe/article/PIIS2666-7...