A piece in the @nytimes today asserted that the UK “quietly updated its vaccination playbook to allow for a mix and match regimen".

This is both strictly true and entirely misleading.
#mixandmatch #vaccine
Thread... https://www.nytimes.com/live/2021/01/02/world/covid-19-coronavirus

It is NOT now UK policy to give whatever vaccine is at hand for the second shot. But it is an option for a tiny number of individuals where it is not known which vaccine was given first.

Lets say someone shows up for their second dose and they have lost their card (I have lost mine - luckily I photographed it!) or changed GPs.

If they are at high risk and they may have difficulty attending again then it “it is reasonable to offer one dose of the locally available product to complete the schedule”.

This is a quote from the "Green Book".

The Green Book is our (excellent) UK vaccine bible put together by the Joint Committee on Vaccination and Immunisation at Public Health England.

The language of the article is highly prejudicial. Of course the update was quiet. Ammendments are typically made without fanfare. Because, whilst it is surprisingly readable, it's ultimately a technical document for professionals.

And why call it “the Vaccination playbook”. Playbook is a word that we generally use to describe underhand industry tactics. “The Tobacco industry playbook”.

Anyway it’s really clear about the schedule for Pfizer and Astra Zeneca vaccines - 2 doses 21 or 28 days apart.

There IS a footnote.

"Every effort should be made to determine which vaccine the individual received and to complete with the same vaccine."

it goes on...

"For individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule."

"This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again."

"In these circumstances, as both the vaccines are based on the spike protein, it is likely the second dose will help to boost the response to the first dose. For this reason, until additional information becomes available, further doses would not then be required."

So basically if all else fails then it's better to give a second dose of a different vaccine than nothing at all - totally sensible.

I'm a big fan of sticking to the available evidence when it comes to vaccines and that's exactly what we are doing.