Comparative study of SARS-CoV-2 omicron and delta mutant infections in the United Kingdom

In a recent study posted on medRxiv* UK (UK) researcher Preprint Server has conducted an epidemiological cohort study to determine the difference in infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicrons and delta variants in the UK. Was evaluated.

In the United Kingdom, the SARS-CoV-2 omicron variant (B.1.1.529) prevailed and rapidly replaced the delta variant (B.1.617.2) in January 2022. Studies have shown that the Omicron variant is associated with increased infectivity and decreased vaccine efficacy compared to other SARS-CoV-2.

In the current study, researchers used secondary incidence and household clustering to assess the infectivity of both Omicron and Delta variants during an epidemic in the United Kingdom.

Research design

The current study was conducted between 5 and 11 December 2021 in the United Kingdom, where both Omicron and Delta were co-circulating. A positive SARS-CoV-2 result was reported by the United Kingdom National Health Service (NHS) Institute to the UK Medical Security Agency (UKHSA). Lab reports containing immunochromatographic (LFD) test data were stored in UKHSA’s Second Generation Surveillance System (SGSS).

Omicron and delta variants were defined by genomic sequencing and genotyping of confirmed polymerase chain reaction (PCR) cases, and S gene targeting disorder (SGTF). The UK genomics sequence was held in the cloud infrastructure of the Big Data Microbial Bioinformatics Database (CLIMB) and was coordinated by Coronavirus Disease 2019 (COVID-19) Genomics, UK (COGUK).

Vaccination data for COVID-19 in the United Kingdom was obtained from the National Immunization Management System (NIMS). Data for SARS-CoV-2 positive individuals is sent for contact tracing using nationally matched data (NHS test and trace records), and the assessment of infection to the specified contact is this data. Was run using. Two or more SARS-CoV-2 positive cases in the same home with the same unique asset reference number (UPRN) were defined as a household cluster.

Survey results

During the study, researchers observed an average of 2.0 contacts per case with the Delta variant and 1.7 contacts with the Omicron variant, of which 1.6 and 1.1 were home contacts with Delta and Omicron, respectively, and 0.4 and 0.6 non-. It was a home contact. If the exposure was inside and outside the household, the median consecutive intervals to secondary cases were 4 and 3 days for Delta and Omicron, respectively.

The cycle threshold (CT) values ​​for the nucleocapsid and open reading frame (ORF) 1ab genes in delta cases (98.7%) and omicron cases (99.2%) were <30 days. The unadjusted secondary incidences of Omicron and Delta were 15.0% and 10.8%, respectively, among the designated household contacts, while they were 8.2% and 3.7%, respectively, for non-household contacts.

The team noted that in the Omicron case, the overall risk of infection to home contact was 1.48 and in the non-home contact it was 2.14, compared to the Delta case. In the non-home environment, the secondary incidence of exposed contacts to the three-vaccinated Delta was 3.0% compared to 5.1% for unvaccinated contacts. Similarly, in the home environment, it was 7.6% compared to 12.9% respectively.

When the number of vaccinations was reduced from 3 to no dose, the infection rates in the non-home environment were 3.1% vs. 4.9%, respectively, while in the home environment they were 6.2% vs. 11.8%, respectively. Similarly, the adjusted rate risk of infection in non-home cases receiving a third dose of the vaccine was 0.51 compared to the two doses, whereas in the case of home contact, the rate was 0.68. ..

The team analyzed that in a home environment, individuals who received three doses showed a protection-adjusted risk ratio for contacts (0.88) or exposed (0.78) compared to two doses. In non-home contact, it was 0.76, but no difference was observed in the exposed.

Researchers found that unvaccinated home contact in unvaccinated Omicron cases had a secondary incidence of 16.2%, compared with 14.6% in unvaccinated Delta cases with an adjusted risk ratio of 1.11. I showed that it was. For non-home contact, 11.6% of unvaccinated Omicron cases and 6.3% of unvaccinated Delta cases had an adjusted risk ratio of 1.84.

The team includes contacts of all ages, especially children, 30-39 years old (except 40-49 years old), males (compared to female contacts), and exposed persons under 30 years old (compared to female contacts). Compared to exposed people aged 30-79 years). Non-home contact exposure. Children under the age of 20 had a lower risk of infection than those between the ages of 30 and 69.

Compared to the East Midlands (reference area), non-household contact with exposed persons in London was more likely to be a case, and household contact in the northwest was less likely to be a case.Researchers observed that of the 13.5% delta and 8.8% omicron asymptomatic cases reported at home exposure, half of the cases had a probability. [adjusted odds ratio (aOR) 0.47 (0.44-0.51)] For communication to their home contacts compared to symptomatic cases.

For the Omicron variant, the overall risk ratio for household clustering was 3.54 compared to the Delta variant. In addition, depending on vaccination status, the risk of household clustering with the Omicron mutant was increased compared to Delta, especially in first-episode patients 14 days or more after the third dose of vaccine. In addition, the team is the proband of the young case (<30歳）と黒人の民族グループは、それぞれ> We observed that the probability of household clustering was low compared to the 40-year-old Caucasian ethnic group.

In a restricted model that included individuals with travel history outside the UK, the overall adjusted odds ratio for household clustering of Omicron probands was 4.53 compared to 4.51 for Delta, but cases with overseas travel history No significant changes were seen in the excluded models. England.

Conclusion

The results of this study showed a higher risk of infection from the SARS-CoV-2 omicron type compared to the delta type in both home and non-home configurations. It also showed a significant reduction in the protective effect of COVID-19 booster vaccination in reducing anterior infections from Omicron cases compared to delta variants.

This study identifies and understands the effects of newly emerging SARS-CoV-2 variants on hospitalization, disease cases, and death, and publicly includes the deployment of booster immunization against these newly emerging variants. He emphasized the need for genomic surveillance to accelerate hygiene intervention. ..

*Important Notices

medRxiv publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.