Omicron largely evades immunity from a previous infection or two doses of the vaccine | Empire News

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The Omicron variant largely avoids immunity from previous infection or two doses of the vaccine according to the most recent imperial modeling.

The new report (Report 49) from the Coronavirus Response Team at Imperial College London estimates that the risk of reinfection with the Omicron variant is 5.4 times greater than that of the delta variant. This means that the protection against reinfection by omicron provided by a previous infection may be up to 19%.

Researchers estimate growth and immune escape of the Omicron variant in England. They used data from the UKHSA and the NHS for all PCR-confirmed SARS-CoV-2 cases in England who underwent COVID testing between 29 November and 11 December 2021.

This level of immune evasion means that Omicron poses a major and imminent threat to public health. Professor Neil Ferguson

The study includes people identified as having omicron infection due to S gene target failure (SGTF), as well as people with genotype data that confirmed omicron infection. Overall, 19,463 individuals without gene target S failure (likely to have another variant) and 11,329 cases (likely to have Omicron) were included in the SGTF analysis, as well as 122,063 delta and 1,846 Omicron cases in Genotype analyses.

omicron growth

First, the report looks at factors associated with a positive test for Omicron compared to non-Omicron (mostly Delta) cases. The results indicate that the proportion of Omicron among all COVID cases was doubling every two days through December 11, estimated from both S-gene Target Failure and genotype data. Based on these results, they estimated that the reproduction number (R) of Omicron was higher than 3 during the studied period.

The distribution of Omicron by age, region and ethnicity currently differs markedly from Delta, with people aged 18–29 years, residing in the London area, and those of African ethnicity having significantly higher rates of Omicron relative to Delta. London is far ahead of other English regions in Omicron frequency.

The omicron transmission was not uniformly distributed across the population. However, the researchers note that due to its immune evasion, the age distribution of Omicron infection in the coming weeks may continue to differ from delta.

The study found no evidence that Omicron is less dangerous than Delta, judged either by the proportion of people who tested positive for symptoms, or by the proportion of cases seeking hospital care after infection. However, hospitalization data remains very limited at this time.

Re-infection rates

To assess the effect of Omicron on re-infection rates, the researchers used genotype data, because even before Omicron, re-infection was associated with negative S gene target failure data, most likely due to random PCR target failure caused by lower re-infection-related viral loads.

By controlling for vaccine status, age, gender, race, asymptomatic status, region and sample history, O’Micron was associated with a 5.40 (95% CI: 4.38–6.63) times higher risk of reinfection compared to Delta. To put this in context, in the pre-Omicron era, the UK ‘SIREN’ study of COVID infection in healthcare workers estimated that prior infection provided 85% protection against a second COVID infection over 6 months. Risk estimates again in the current study indicate that this protection was reduced to 19% (95% CI: 0-27%) against omicron infection.

Vaccine efficacy against Omicron

The researchers found a significantly higher risk of omicron symptoms than delta for those who exceeded the second vaccine dose by two or more weeks, and two or more weeks after the booster dose (AstraZeneca and Pfizer).

Depending on the estimates used for vaccine efficacy against symptomatic infection from the delta variant, this translates into estimates of vaccine efficacy against symptomatic omicron infection between 0% and 20% after two doses, and between 55% and 80% after a booster dose. Similar estimates were obtained using genetic makeup data, albeit with greater uncertainty.

Professor Neil Ferguson of Imperial College London said: “This study provides further evidence of the very large extent to which Omicron can evade prior immunity resulting from infection or vaccination. This level of immune evasion means that Omicron poses a major and imminent threat to public health.”

Professor Azra Ghani from Imperial College London said: “Determining the risks of reinfection and the efficacy of a vaccine against Omicron is essential to modeling the potential future course of the Omicron wave and the potential impact of vaccination and other public health interventions.”

The work, which has not yet been peer-reviewed, is presented in the latest report from the WHO Collaborating Center for Infectious Disease Modeling within the MRC Center for Global Infectious Disease Analysis, Jameel Institute, Imperial College London.

Since the emergence of the novel coronavirus (COVID-19) in December 2019, the Coronavirus Response Team at Imperial College has adopted a policy of promptly sharing research findings on the evolving pandemic.

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Read the full report “Report 49 – Growth, population distribution and immune escape of Omicron in England”

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