Individuals who have had two vaccine doses can be just as infectious as those who have not been jabbed.
Even if they have no or few symptoms, the chance of them transmitting the virus to other unvaccinated housemates is about two in five, or 38%.
This drops to one in four, or 25%, if housemates are also fully vaccinated.
The Lancet Infectious Diseases work shows why getting even more people vaccinated and protected is important, they say.
Unvaccinated people cannot rely on those around them being jabbed to remove their risk of getting infected, they warn.