I’ve been meaning to write an update on the Omicron variant of concern for a few weeks’ now and it’s now or never, so here we go! The Omicron variant has a host of mutations compared with previous variants, which seems to have given it the ability to spread much more rapidly. This may well be due in part to the ability to side-step antibody mediated immunity obtained through previous infection and vaccination. Omicron is spreading rapidly in the community. We don’t yet know what impact the current rapid community spread will have on hospitalisations and ultimately deaths, so time will tell.  

UKHSA published a neat epidemiological summary focussed on Omicron a few days ago (and key points summarised even more neatly in the associated risk assessment). Here are the key points:

• Omicron is more transmissible than other variants. UK data on household contacts shows a secondary attack rate for Omicron of 22% compared with 11% for Delta; put another way, Omicron is almost exactly twice as transmissible as Delta.
• There is emerging evidence of an increased reinfection rate.
• The Omicron variant has many mutations compared with other circuiting variants of concern. Many of these are on the surface proteins, meaning that it has ‘vaccine escape’ properties:
  • Laboratory data suggests that antibodies produced through vaccination are less effective against the Omicron variant compared with Delta.
  • Vaccine effectiveness data is significantly lower against Omicron compared with Delta, especially for the AZ vaccine.
  • Booster vaccination make a real impact in improving vaccine effectiveness.
• Due to a combination of the above, and maybe for some as-yet unidentified reasons, Omicron is spread fast. Very fast. Very very fast. When this report was published, just 7 days ago (albeit with a data cut off a little before then), there had been 260 Omicron cases reported in the UK. Omicron is now the dominant variant certainly in London and probably in the country. And we saw yesterday a record number of cases reported nationally, pushing 100k, and meaning that we might soon need a new y axis to report the number of daily cases.
• It is too early to tell whether or not the rapid rise in community infection will result is a rise in patients admitted to hospitals, a requirement for critical care, and ultimately deaths. There’s typically a two week lag between an increase in community infections, and an increase in hospitalisations, and a further two week lag between increased hospitalisations and deaths. We are seeing the rapid rise in community infections now, so we need to wait and see what happens in the UK regarding hospitalisations. Some data from South Africa provides a glimmer of hope that the virus has ‘sacrificed’ virulence for transmissibility.
• There is no evidence that Omicron causes diagnostic challenges to existing test methods (including lateral flow and PCR).
• There’s no evidence that the transmission routes of the virus have changed fundamentally – and this is unlikely because it’s still the same virus!

So, what does all this mean? From a community viewpoint, a lot of people in the UK will be having COVID-19 for Christmas. I would encourage everybody to socialise carefully over the next couple of weeks. From a hospital viewpoint, it’s a very uncertain time. I think we have enough evidence to know that Omicron is less virulent. But given the larger pool of people who are becoming infected, including some of the vaccinated vulnerable, it does seem likely there will be an increase in hospitalisations. But we just don’t know how big this will be. As Dr Susan Hopkins said earlier in the week, there’s a wave coming, so we need to prepare for the worst and hope for the best.