https://www.ons.gov.uk/peoplepopulationandcommunity/birthsde...
Or are you referring to the deaths from covid?
I suppose conceivably there is a strong adverse selection/sorting effect happening, but I’m not sure that fits with the pattern. Need to think about it. (Note also the upward trend of the second-dosed.) I think it’s more likely an issue with the way the data is collected.
I don't have time to look into it right now, but if that were the case we should expect the mortality rate for single-dosers to go up two weeks after their first dose in countries with a two week gap between doses and twelve weeks after their first dose in countries with a twelve week gap (i.e. people in the 12 week gap countries who are 6 weeks after dose 1 should have much lower mortality than people in the 2 week gap countries who are 6 weeks after dose 1 and have not gotten a dose 2, even after controlling for age and comorbidities).