Correction 23 December 2021
We have corrected an error in the fifth paragraph of this statement. The previous version read “There are 1,701 positive individuals included in the analysis…” It should have read “There are 1,816 positive individuals included in the analysis..."
This happened because of a human error.
Characteristics associated with the Omicron variant
Today we have 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. These early results are based on the first fortnight’s data that have sufficient cases for analysis on the Omicron variant, so caution is advised. Fuller analysis based on more data from our survey will be published when available.
Cases compatible with the Omicron variant are characterised by the absence of the S gene on a positive test, which is 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.
Today’s data release is available.
This analysis evaluates the characteristics of those who tested as a strong positive (cycle Threshold (Ct) value <30) between 29 November 2021 and 12 December 2021 and 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 1,816 positive individuals included in the analysis, of which 115 tested positive compatible with Omicron. See note at end of document for the definition of “compatible with Omicron” and “compatible with Delta”.
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<30) are included, since weaker positive results of the Delta variant could be identified as compatible with Omicron. The model identifies the probability of these individuals having positive results 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.
Deprivation: those infected with COVID-19 who live in more deprived areas are more likely to test positive with infections compatible with the Omicron variant.
Urban: those infected with COVID-19 and living in major urban areas and urban cities or towns are more likely to test positive with infections compatible with the Omicron variant compared with those living in rural areas.
Ethnicity: there is some evidence to suggest that people who test positive for COVID-19 and report being from ethnic minorities are more likely to test positive with infections compatible with the Omicron variant compared with those who identify themselves as White.
Traveling abroad: those who travelled abroad in the last 28 days and test positive for COVID-19 are more likely to test positive for infections compatible with the Omicron variant compared with those who did not travel.
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 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, though individuals who had received at least one dose of a COVID-19 vaccine continued to be less likely to test positive for COVID-19, regardless of variant. It is too early to draw conclusions from our data on the effectiveness of vaccines against the Omicron variant.
The analysis is based only on individuals who test positive with a high viral load (Ct < 30) and have gene pattern OR + N, OR + N + S, OR + S or 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, and gene patterns OR + N + S, OR + S and N + S are defined as being compatible with Delta.
It is possible that some OR + N cases may not be Omicron 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 (>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.