6.Is there any evidence that children exposed to many different viruses early in life have a better immune system?

There is a good bit of data about what happens when young children are not exposed to many viruses early on. Much of this comes from pre-Covid comparisons of children who start nursery as babies or toddlers, and children who are not enrolled in group child care until they are older, if at all. Unsurprisingly, children are particularly prone to infections in the early months after they start mixing with larger groups of children, regardless of their age at the time. Thus, a 3-year-old who goes to the nursery for the first time is likely to get more colds or other bugs at that time than a 3-year-old who has been at nursery for a year or two already. 

Moreover, the authors of a Danish study based on data of children born between 1997 and 2014 up until the age of 20, made another discovery: being enrolled in group childcare and thus exposed to infections early on is linked to a “modest increase” in the average number of times a child has to be prescribed antibiotics throughout their childhood.

Also from Denmark, we have good evidence as to what happened to the cohort of children who were babies in 2020/21, the winter with a very low rate of RSV due to Covid protections: they are less likely to have been hospitalised with RSV since Covid mitigations were removed compared to babies born in 2022.

The short answer to this question appears therefore to be ‘no’.