So let's see where things are at with Omicron post-Christmas....
The information regarding Omicron is still evolving and we are in the early stages. So far Omicron appears to be more infectious than Delta and other variants. Some estimates show that Omicron is now the second most infectious virus on the face of the earth after measles.
The information from two studies in the U.K. show that Omicron produces 40% to 70% fewer severe cases than Delta (based on the U.K. population which is approx. 82% vaccinated). However one of the studies noted an increase in severity for Omicron among the unvaccinated when compared to Delta.
The information from South Africa indicates that over 90% of those who were hospitalized with Omicron are unvaccinated (unchanged from Delta) They also noted an increase in the number of children hospitalized with Omicron when compared to Delta. The information from South Africa noted that only 6% of those hospitalized with Omicron were in ICU compared to over 18% with Delta. About 25% of the population of South Africa is fully vaccinated.
There are estimates in the U.K. that 80% of those hospitalized with Omicron will be unvaccinated compared to numbers close to 90% with Delta. This is reflective of increasing vaccination rates in the U.K. as well as the likelyhood that Omicron is more vaccine evasive. The concept of base rate fallacy must be kept in mind when attempting to do comparisons.
There are lab experiments involving neutralizing antibodies and vaccines which shows that Omicron appears to be more vaccine evasive. The expectation is that there will be more breakthrough cases with Omicron (which appears to be occurring). With Delta the breakthrough case rate was below 0.5% generally. With Omicron this may increase significantly. Note that most vaccines (measles, mumps, etc.) have over a 3% breakthrough infection rate in a population with high prevalence of the disease.
The ability of Omicron to breakthrough is not limited to vaccines -- there are studies showing that previous Covid infection in the unvaccinated provides nearly no protection against Omicron.
So in summary - at this point Omicron appears to be more vaccine evasive, previous infection provides little protection, more infectious, and less severe. The next few weeks will provide better insights on the realities.
