How effective is one Covid vaccine dose?

Available for over a year

Would it make more sense to vaccinate more people by delaying the second doses of vaccines for Covid 19? That is a debate going on at the moment. The UK has decided to delay the second dose for up to three months. We recently received an email from a listener who says he first heard that the Pfizer/BioNtech vaccine was 52% effective after the first dose and 95% after the second. Now he has been told that the first dose now has an effectiveness of 90%. Which is correct? Tim Harford looks into it. Plus, is a new Variant first spotted in the UK really 70% more transmissible than previous variants? Presenter: Tim Harford Producer: Kate Lamble and Charlotte McDonald