Has Boris Johnson done enough to stop the Omicron variant?

The restoration of an obligation to take a PCR test within two days of return to the UK, and to isolate until receipt of a negative result, is the most important of Boris Johnson’s announcements today.

In theory it will delay the seeding and spread of the new Omicron Covid-19 variant.

But the relatively limited prophylactic measures unveiled alongside this – compulsory mask wearing in shops and on public transport, the obligation for any close contacts of those infected with Omicron to isolate, whether or not they test positive – will only turn out to be adequate if the new variant hasn’t already been seeded here.

It is possible that there is more of Omicron in the UK than we know. And if it is, we’ll see more of what the PM called his plan B against Covid-19 – vaccine passports for entry to entertainment and hospitality, encouragement to work from home – within days.

We should have more data very soon about the magnitude of the immediate problem we face

One bit of good news is that NHS Test and Trace should be able to establish rapidly the prevalence of Omicron, prior to genome sequencing, because more than one-third of PCR tests are able to distinguish it from the Delta variant (in a slightly crude way, but which allows those tests to be prioritised for sequencing).