I work in biopharma and regulatory, and have analysed parts of this vaccine as part of my job. I can't say more than that.

So, how has the Pfizer mRNA vaccine been approved in UK by the MHRA and not EMA? You have to bear in mind that the EMA is an overseer, it is an organisation made up individual member states national health authorities (or two in the case of Germany, PEI and Bfarm. This is much like CBER and CDER for those of you familiar with the FDA). An approval from EMA will have to come via the national authorities of each member state sent up via the bureaucracy, then rubber stamped at the top. It is no surprise that the EMA is slower than the MHRA acting alone.

Secondly, there is a cultural difference. The MHRA has always been at the forefront of regulatory approval of new technology, it is one of it's strengths, and will have experience of mRNA technology before. Other big regulatory agencies have their own characters - Paul Ehrlich Institute (German biologics regulator) is famous for its rigorous level of technical detail and questioning for example. In my experience the French just get in the way, but that is an aside.

Two things then. Smaller organisation with less bureaucracy is more nimble. MHRA is also less risk adverse and due to the early phase hotbed of biopharma in the UK likely has more experience on these novel vaccine modalities.