It was mentioned at the beginning of the pandemic that the MMR vaccine may provide some protection from Covid-19 and could be the reason that children don't get sick/as sick as older people. The scientists think it's the mumps part that is doing this and have been studying it.
From the link: "This is the first immunological study to evaluate the relationship between the MMR II vaccine and COVID-19. The statistically significant inverse correlation between mumps titers and COVID-19 indicates that there is a relationship involved that warrants further investigation,"
https://medicalxpress.com/news/2020-...ne-covid-.html