Earlier this week, we published some early results from the Coronavirus (COVID-19) Infection Survey showing the characteristics of people more likely to be infected with the Omicron variant compared with the Delta variant. Today, we are updating these results based on more recent analysis. These are still early results from our data including positive infections compatible with the Omicron variant, so caution is advised.
Cases compatible with the Omicron variant are characterised by the absence of the S gene on a positive test, one of three genes that a PCR test detects, the others being OR and N, and a high viral load. Cases with a high viral load and an absent S gene are characterised in this analysis as a potential Omicron case. All other cases are likely to be cases of the Delta variant or its genetic descendants.
While fortnightly estimates provide a timely picture, the results can fluctuate from one fortnight to another depending on the data collected in that specific time period. This means that findings that were significant in one period may not necessarily be significant in another period. This may be because the effect of a characteristic is genuinely changing, or because we do not have sufficient individuals with that characteristic in a particular fortnight to exclude the possibility of differences found being because of chance.
Today’s data release is available.
This analysis evaluates (for those who tested as a strong positive (cycle threshold (Ct) value less than 30) between 03 December 2021 and 16 December 2021) the characteristics which were associated with individuals who had results compatible with the Omicron variant. Results not compatible with Omicron are suspected Delta cases. These effects show the relative likelihood of having a result compatible with Omicron compared with the reference group for each characteristic studied.
There are 2,091 positive individuals included in the analysis, of which 495 tested positive compatible with Omicron (see Further information).
The model uses a similar process to our usual predictors of positivity analysis, published regularly in our Characteristics of people testing positive release. However, only individuals who test as a strong positive (Ct value less than 30) are included, since weaker positive results of the Delta variant could be identified as compatible with Omicron.
Age: compared with other ages, young children testing positive for coronavirus (COVID-19) are less likely to have infections compatible with the Omicron variant; those aged in their 20s and 30s with COVID-19, however, are more likely to have infections compatible with the Omicron variant compared with other ages.
Deprivation: these latest data do not show an effect of deprivation on the likelihood of testing positive with an Omicron compatible result in those who test positive for COVID-19.
Urban: those infected with COVID-19 and living in major urban areas and urban cities/towns are more like to test positive with infections compatible with the Omicron variant compared with those living in rural areas.
Household size: those infected with COVID-19 and living in households with more people are less likely to test positive with infections compatible with the Omicron variant compared with those living in households with fewer people.
Ethnicity: there is some evidence to suggest that people who test positive for COVID-19 who identify as being from an ethnic minority background are more likely to test positive with infections compatible with the Omicron variant compared with those who identify as White.
Reinfection: those who have previously been infected with COVID-19 and become reinfected are more likely to test positive for an infection compatible with the Omicron variant, compared with those who test positive with their first infections.
Vaccination status: those who have received two or three doses of a vaccine and test positive for COVID-19 are more likely to be infected with infections compatible with the Omicron variant compared with those who are unvaccinated and test positive; it is too early to draw conclusions from our data on the effectiveness of vaccines against the Omicron variant.
This analysis is based only on individuals who test positive with a high viral load (cycle threshold (Ct) value of less than 30) and have one of these gene patterns:
- OR + N
- OR + N + S
- OR + S
- N + S
Since the S gene is not detected in strong positive cases infected with the Omicron variant, those with gene pattern OR + N are defined as being compatible with the Omicron variant. The following gene patterns are defined as being compatible with the Delta variant:
- OR + N + S
- OR + S
- N + S
It is possible that some OR + N cases may not be the Omicron variant as some genes may not be detected (for example, weaker Delta infections). However, limiting the analysis to cases with a high viral load should minimise this. Some OR + N + S, OR +S, and N + S cases may not be Delta, as other variants may be circulating in small numbers, but sequencing suggests the majority (more than 99%) of such cases will be Delta.
Any cases with a low viral load or with different gene patterns are not included in the analysis.
All results adjust for all other factors in the model, as described in our Characteristics of people testing positive release.