In the USA, the new rotavirus vaccine is protecting those who have had the vaccine - and many who have not been vaccinated. Rotavirus causes severe gastroenteritis and the vaccine was introduced for babies in the USA in 2006.
There has been dramatic reduction in hospital admissions for gastroenteritis in the age group that were vaccinated.
Groups that were too old to have been vaccinated - older children, adults and even elderly adults also showed a marked reduction in admissions for rotavirus.
This is a demonstration of "herd immunity" in action. The fewer people there are in the community who are susceptible to a virus, the less the virus gets passed around. And if you've ever had anything to do with a sick baby or child, you will know how good they are at sharing their infected body fluids with the whole family.
Rotavirus is a major killer of young children in poor countries, so if this vaccine could be used in such places it could have a significant impact.
It is licenced in the UK but is not on the NHS routine vaccination list. Maybe it should be.