Demographic and clinical comparison of the first and second COVID-19 waves in London, UK

The B.1.1.7 variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in the UK in late 2020 and marked what has been termed the “second wave” of the coronavirus disease 2019 (COVID-19) pandemic in the UK. The B.1.1.7 variant has been associated with increased transmissibility compared to the wild-type variant, and became the dominant strain within months. Anecdotally, though supported by a small number of studies in other countries such as Japan, the average COVID-19 patient requiring hospitalization during the second wave was younger, and less likely to bear comorbidities.

In a paper recently uploaded to the preprint server medRxiv*, clinical and demographic data from across the UK is compared to viral genome sequence data, identifying trends amongst the population affected, and across SARS-CoV-2 strains.

How was the study performed?

Electronic health data regarding COVID-19 patients from five hospital trusts located in London was collected from between the period March 13, 2020, to February 17, 2021, and divided amongst six categories: outpatients, NHS employees, non-hospitalized, hospitalized, hospital-acquired cases, and interhospital transfers. Whole genome sequencing of residual patient samples following PCR testing was performed to obtain the SARS-CoV-2 genetic sequence, and the lineage assigned by computational comparison with known genomes. Age, sex, socioeconomic status, ethnicity, medical history, and other demographic data were also collected for each of the nearly 6,000 individuals included in this study.

The group assigned the first wave as the period from the start of the study until mid-May, when a baseline level of just 5-20 cases per day was reached and maintained for several months until the start of the second wave, in early October. The dividing point between the two waves, then, was said to be July 25, the mid-point. The first wave consisted of 26.3% of the cases, with wave two being almost three times larger.

What trends were observed?

The group noted that there was a slight decrease in the average age of patients in the second wave, being 62 years in the first and 60 in the second. Women were also more common in the second wave, being 41.8% of all cases in the first and 47.3% in the second. Additionally, those in the second wave were less likely to bear comorbidities such as frailty, or have a history of stroke or cancer.

Other comorbidities such as diabetes, kidney disease, hypertension, or cardiovascular disease were equally represented in both waves one and two, while obesity was actually more common amongst COVID-19 patients in the second wave. An equal proportion of patients suffered from hypoxia and other severe SARS-CoV-2 symptoms in both waves.

Patients in wave one were each assumed to be of the non-B.1.1.7 lineage of SARS-CoV-2, as the variant had not yet been discovered by this time. However, data collected during the second wave allowed the group to compare demographic and clinical data related to strain. On average, those with the B.1.1.7 variant of COVID-19 were slightly older, 64 compared to 62, and had no difference in ethnicity, though were more likely to be women. 48% of those with the B.1.1.7 variant were women, compared with 41.8% of those with the non- B.1.1.7 variant being women in the second wave, the same ratio between men and women observed in wave one. Additionally, those with the B.1.1.7 variant were less likely to be frail while being more likely to be obese, as observed in the general trend between first and second waves. 70% of those with the B.1.1.7 variant of SARS-CoV-2 were hypoxic upon hospitalization, compared with 62.5% of those with the non-B.1.1.7 strain. However, biomarkers of inflammation were identical or, in fact, lower amongst those with the B.1.1.7 strain.

The group suggests that this is consistent with the observed enhanced virulence of this strain, and potential increased virulence in females. Indeed, other studies have suggested that females are more likely to require hospitalization and suffer poor outcomes from the B.1.1.7 strain. With regards to the apparently lower rate of frail individuals requiring hospitalization, the group explains that lower nursing home relocation and greater shielding protocols meant that such individuals were less likely to report to the hospital.

Importantly, it was found that despite enhanced social distancing measures and more widely committed mask-wearing coming up to the beginning of the second wave, non-hospitalized COVID-19 patient numbers remained approximately equivalent between each wave. However, the enhanced virility of the now dominant B.1.1.7 strain combined with greater testing capacity likely contributed to these figures, with a larger number of asymptomatic individuals being identified.

*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.

Journal reference:
Michael Greenwood

Written by

Michael Greenwood

Michael graduated from Manchester Metropolitan University with a B.Sc. in Chemistry in 2014, where he majored in organic, inorganic, physical and analytical chemistry. He is currently completing a Ph.D. on the design and production of gold nanoparticles able to act as multimodal anticancer agents, being both drug delivery platforms and radiation dose enhancers.

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