Under 40s vaccine choice

I'm not under 40 so can't reply personally to your question but I found this which might be of interest.

An alternative should be preferentially offered according to guidance.

JCVI guidance states ?in addition to those aged under 30, unvaccinated adults aged 30 - 39 years who are not in a clinical priority group at higher risk of severe COVID-19 disease, should be preferentially offered an alternative to the AstraZeneca COVID-19 vaccine, where possible and only where no substantial delay or barrier in access to vaccination would arise.

This is taken from JCVI announcement regarding AstraZeneca Vaccine and next steps, the full guidance can be found at https://www.england.nhs.uk/coronavirus/wp-content/uploads/sites/52/2021/05/C1279-jcvi-announcement-regarding-astrazeneca-vaccine-and-next-steps-7-may-2021.pdf

There is a table on this page that outlines the possible risks for various ages https://www.gov.uk/government/publications/covid-19-vaccination-and-blood-clotting/covid-19-vaccination-and-blood-clotting#which-vaccine-will-you-be-offered I remember it being reported the risk was less than a car journey many of us probably did without thinking before all this. Horrible for those who suffer and their loved ones but that needs to be weighed up against the availability of an alternative / wait for vaccination and the high chance of catching Covid which could result in disease or long Covid. I?m glad I have no choice I?ve already had my first dose and the guidance is clear I have to have the same second dose.

The risk is most acute for younger females, those who smoke and females who take the pill.

If I was in one or more of these categories then I would definitely ask my GP for a non-AZ jab, this is unlikely to be a problem since Moderna (as well as Pfizer) are in good supply.