Thread by @BillHanage

To what does Omicron owe its remarkable properties? Immune evasion or inherent transmissibility. My bet is a bit of each. One thing though is beyond question - it is much better than delta at spread. Look at the household attack rate. This has implications 1/n

So Omicron is infecting roughly 2-3 times as many people as Delta, specifically in the setting of household transmission. It is not as clear outside households but remember, it is much harder to identify all potential contacts outside households 2/n

(That data btw was from last week's amazing technical briefing from @UKHSA. assets.publishing.service.gov.uk/government/upl…) 3/n

From the same document look at the proportions of early Omicron cases without known links to travelers as it was getting started in the UK. That's a lot. What could explain this and subsequent dynamics? 4/n

SARS-CoV-2 and other coronas show a tendency to super spreading (or overdispersion of the transmission parameter). In layman's terms this means that a minority of infections transmit much much more than others 5/n pubmed.ncbi.nlm.nih.gov/32685698/

Taking these things together, Omicron appears roughly 2-3 times as likely to transmit as Delta, and is expected to show a tendency to clustered transmission in large gatherings. Now overlay that onto the holiday season, and parties 6/n

The math of superspreading has two parts. First the larger the gathering the greater the probability someone attending is infectious by chance, but it also determines the potential size of any resulting cluster. Now think about an attack rate 2-3 times more than delta 7/n

So if you want to avoid participating in a superspreading event either as the spreader or the spreaded to - avoid large gatherings when Omicron is in town OR make good use of rapid tests. What do I mean by 'good use'? 8/n

Do not test only when symptomatic. Test as close in time to the party as possible. Early data suggest viral loads in Omicron can become very high, very quickly. This means a negative test in the morning is not a guarantee of still being negative that evening 9/n

Of course this assumes tests are available. Which is less likely to be the case right now... telegraph.co.uk/news/2021/12/1… 10/n

If you are planning on spending Christmas with family members who might be more vulnerable to the virus, do what you can to avoid giving them something other than presents 11/end