But there's a big question mark over whether these tests would actually detect asymptomatic infection.

Here, they will get a mild cold, more likely an asymptomatic infection, and be set for life.

Researchers said there were also lower rates of asymptomatic infection in the vaccinated groups.

Widely dispersed minor outbreaks of mild and asymptomatic infection would leave a core of fit and immune people to deal with more intense outbreaks.

Clinical manifestations range from asymptomatic infection to severe illness.