In a recent study posted to the medRxiv* preprint server, researchers utilized data from the recent rounds of the REal-time Assessment of Community Transmission-1 (REACT-1) study to document the transmission dynamics of severe acute respiratory syndrome coronavirus disease 2 (SARS-CoV-2), mainly focusing on the Omicron variant in England during January 2022.

Study: Post-peak dynamics of a national Omicron SARS-CoV-2 epidemic during January 2022. Image Credit: Yana Kho/Shutterstock

Background

The ongoing coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 is marked by the emergence of several mutated SARS-CoV-2 variants since it emerged in 2019. The heavily mutated SARS-CoV-2 Omicron variant that emerged in November 2021 has replaced the previously dominant Delta variant in many countries. Further, Omicron has resulted in the highest ever documented SARS-CoV-2 cases due to its high transmissibility worldwide. By late December 2021, Omicron has become the dominant SARS-CoV-2 variant in the United Kingdom (UK).

About the study

In the present study, the researchers evaluated the round 17 data from the REACT-1 study to determine the characteristics of Omicron transmission in the UK. The REACT-1 study has been characterizing the transmission dynamics of SARS-CoV-2 through the reverse transcription-polymerase chain reaction (RT-PCR) test results of the self-administered throat and nose swab from randomly selected participants aged five years or older roughly from May 2020. The data from REACT-1 study is free from biases and delays associated with SARS-CoV-2 case incidence data and hospitalizations and deaths, respectively.

The data collection for round 17 of the REACT-1 study happened from January 5 to 20, 2022. Round 17 provided data on the socio-demographic, temporal, and geographical spread of the SARS-CoV-2 and viral genome sequence and viral load data for SARS-CoV-2-positive swabs.  

Findings

The results indicated that out of the 840,530 invited subjects for round 17 of REACT-1 study, 140,075 registered, and 102,279 returned the self-administered throat and nasal swab on the given date. Of the 102,279 participants, 102,174 produced a valid SARS-CoV-2 RT-PCR test result.

A 4.41% weighted prevalence of swab positivity in the 102,174 valid tests was observed in round 17, more than three times higher than that of the results from round 16 in England. A total of 2,393 lineages were identified from the 3,028 sequenced positive swabs, and 99.2% belonged to Omicron, including one BA.3 sublineage case and 19 BA.2 cases on January 17, 2022, whereas only 19 cases were attributed to Delta. The additive R advantage of the daily growth rate of the BA.2 Omicron sublineage was 0.46 compared to BA.1 and its sub-lineage BA.1.1. 

The region-specific exponential models from the north of England demonstrated a decrease in weighted prevalence within round 17. Two-dose and three-dose vaccinated individuals had significant protection from SARS-CoV-2 Delta infection in rounds 15 and 16, whereas in round 17, vaccinated individuals had lower protection from Omicron.

A drop in prevalence was observed in adults, whereas the opposite occurred in the case of children in round 17. In all ages, the weighted prevalence showed around a two- to 12-fold increase between rounds 16 and 17. In round 17, the highest weighted prevalence was observed in children aged five to seven at 7.85%, whereas the lowest was in individuals aged 75 years or older at 2.46%. Further, the weighted prevalence was also higher between the rounds in every region of England. 

A higher weighted prevalence of household transmission was observed in households with six or more members and one or more children than those with a single member or without children, respectively.

Those with a confirmed history of COVID-19 had a higher weighted prevalence than those with suspected history or no history of the disease. Of the 2,334 swab-positive individuals with a confirmed history of COVID-19, 75.9% provided the date of the latest positive test; however, 153 of the dates were invalid. Nearly 57.3% had a previous positive test within one to 14 days, 7.16% within 15-30 days, and 4.88% within 30 days or more before swab testing.  

Of the 13,865 participants who tested negative and had a confirmed history of COVID-19, 77.5% provided the date of their latest positive test, of which 6.52% were within one to 14 days, 14.7% were within 15-30 days, and 56.0% were within 30 days or more before the swab testing. 

Apart from the care home or healthcare workers, essential workers had the highest risk of SARS-CoV-2 infection. The risk of SARS-CoV-2 was further higher in residents of large households, urban areas, and most deprived areas than single-person households, rural areas, and least deprived areas, respectively, according to the multivariable logistic regression models. 

Conclusions

The study findings indicated the presence of unprecedented levels of SARS-CoV-2 infection in England from December 2021 to January 2022. Further, the study demonstrated that Omicron nearly replaced the Delta variant, and the Omicron sublineage BA.2 had a growth advantage compared to BA.1.

Although a declining trend of SARS-CoV-2 prevalence was observed in adults in January 2022, the increase in prevalence in children could pose a risk to adults. Further, vaccination provided substantial protection from SARS-CoV-2 infection and reduced COVID-19-associated hospitalizations. However, the study highlights the requirement of COVID-19 mitigation measures in addition to vaccination if the very high Omicron infection rate persists, despite Omicron appearing to be associated with a less severe form of COVID-19.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.