How soon until you feel sick after catching someone else's illness? From measles to colds, flu and Covid, our expert guide to when the symptoms will hit...

How soon until you feel sick after catching someone else's illness? From measles to colds, flu and Covid, our expert guide to when the symptoms will hit...

By Jo Waters Published: 06:49 EDT, 23 July 2024 | Updated: 06:49 EDT, 23 July 2024 e-mail View comments Sitting next to someone with a hacking cough on a crowded plane or train, hearing the friend you had a drink with last night has since tested positive for Covid, or your child's schoolfriend has thrown up in the classroom, most of us fear the worst and wonder if, or simply just when, we'll come down with the same lurgy. With summer holidays coming up, Covid infections still circling, and news of measles outbreaks , many of us will be feeling nervous about getting ill with at least one of them. When we do come down with a bug, we often try to work out 'whose fault it was' — a kind of blame game that's often seen in homes and workplaces alike.

But not all infections spread as easily as others. This depends on the interplay of factors, including how robust the infected person's immune system is and the incubation period, i.e.

the number of days it takes for symptoms to appear after someone is infected with a virus. You catch cold or flu by inhaling particles of the virus, usually in a droplet of mucus from someone who is infected, via coughs or sneezes - but also from touching surfaces that have been contaminated, says Professor Eccles But one of the most important factors is the pathogen's reproduction rate (or R rate), .