In the first and second waves of the pandemic, older people were vastly more affected, and around 80 to 90 per cent of those hospitalised with the virus were over 50.
But as the third wave began at the start of the summer, fewer than half of hospitalisations were in over-50s.
It’s not possible to definitively tell why this is, but the glaringly obvious explanation is that by the end of June most people over 50 had been given two doses of Covid vaccine.
This meant older people were more protected and while younger people were catching up with the vaccines, by comparison they became more at risk.
Now the percentage is climbing again and in recent weeks has been back around 70 to 80 per cent.
This is probably partly due to the fact that more younger people are now protected, but there have also been studies suggesting immunity may begin to wane after some months, a view backed up by several experts and partly behind the decision to offer Covid booster jags in Scotland.
These have been delivered slower than expected, with the date from which all over-50s will be able to book their third dose pushed back from October to November.
So far around 755,000 third doses have been given, with thousands more eligible for their booster – having had a second dose more than six months ago – but not yet having received it.
In the meantime, there are still people who haven’t been fully vaccinated the first time around.
The number of 18 to 29-year-olds who have received two doses is still below 70 per cent, compared to almost 100 per cent in over-50s.
Data published by Public Health Scotland on Wednesday also showed that pregnant women are less likely to have had a vaccine.
Just 36 per cent of women aged 35 to 39 who had a baby in September had been given two doses, compared to 81 per cent in that age group in the general population.
Since the rollout began, study after study has shown that vaccines save lives. We need to get them into arms as quickly as possible.