COVID-19 due to the B.1.617.2 (Delta) variant compared to B.1.1.7 (Alpha) variant of SARS-CoV-2: two prospective observational cohort studies

Abstract

BackgroundThe Delta (B.1.617.2) variant became the predominant UK circulating SARS-CoV-2 strain in May 2021. How Delta infection compares with previous variants is unknown.MethodsThis prospective observational cohort study assessed symptomatic adults participating in the app-based COVID Symptom Study who tested positive for SARS-CoV-2 from May 26 to July 1, 2021 (Delta overwhelmingly predominant circulating UK variant), compared (1:1, age- and sex-matched) with individuals presenting from December 28, 2020 to May 6, 2021 (Alpha (B.1.1.7) predominant variant). We assessed illness (symptoms, duration, presentation to hospital) during Alpha- and Delta-predominant timeframes; and transmission, reinfection, and vaccine effectiveness during the Delta-predominant period.Findings3,581 individuals (aged 18 to 100 years) from each timeframe were assessed. The seven most frequent symptoms were common to both variants. Within the first 28 days of illness, some symptoms were more common with Delta vs. Alpha infection (including fever, sore throat and headache) and vice versa (dyspnoea). Symptom burden in the first week was higher with Delta vs. Alpha infection; however, the odds of any given symptom lasting ≥7 days was either lower or unchanged. Illness duration ≥28 days was lower with Delta vs. Alpha infection, though unchanged in unvaccinated individuals. Hospitalisation for COVID-19 was unchanged. The Delta variant appeared more (1·47) transmissible than Alpha. Re-infections were low in all UK regions. Vaccination markedly (69-84%) reduced risk of Delta infection.InterpretationCOVID-19 from Delta or Alpha infections is clinically similar. The Delta variant is more transmissible than Alpha; however, current vaccines show good efficacy against disease.FundingUK Government Department of Health and Social Care, Wellcome Trust, UK Engineering and Physical Sciences Research Council, UK Research and Innovation London Medical Imaging & Artificial Intelligence Centre for Value Based Healthcare, UK National Institute for Health Research, UK Medical Research Council, British Heart Foundation, Alzheimer’s Society, and ZOE Limited.Research in contextEvidence before this studyTo identify existing evidence for differences (including illness, transmissibility, and vaccine effectiveness) from SARS-CoV-2 infection due to Alpha (B.1.1.7) and Delta (B.1.617.2) variants, we searched PubMed for peer-reviewed articles and medRxiv for preprint publications between March 1 and November 18, 2021 using keywords (“SARS-CoV-2” OR “COVID-19”) AND (“delta variant” OR “B.1.617.2”) AND (symptom* OR transmiss* OR “disease duration” OR “illness duration” OR “symptom* duration”). Searches were not restricted by language. Among 169 identified PubMed articles, we found evidence that Delta variant has increased replication capacity (from 4-fold, up to 21-fold, compared with wild-type) and greater transmissibility (estimated between +20% and +97%), compared with previous strains. Currently available vaccines may have 2- to 5-fold lower neutralizing response to Delta vs. previous variants, depending on vaccine formulation, although their protective effect against severe disease and death appears to remain strong. REACT-1 study found that in UK infections were increasing exponentially in the 5-17-year old children in September 2021, coinciding with the start of the autumn school term in England. This was interpreted as an effect of the relatively low rate of vaccinated individuals in this age group. Other studies found that in unvaccinated individuals, Delta variant may be associated with higher odds of pneumonia, oxygen requirement, emergency care requests, ICU admission, and death. In a study of 27 (mainly young) cases, 22 persons were symptomatic, with fever (41%), cough (33%), headache (26%), and sore throat (26%) the commonest symptoms. We found no studies, beyond case series, investigating symptom and/or illness duration due to Delta variant infection otherwise.Added value of this studyUsing data from one of the largest UK citizen science epidemiological initiatives, we describe and compare illness (symptom duration, burden, profile, risk of long illness, and hospital attendance) in symptomatic community-based adults presenting when either the Alpha or Delta variant was the predominant circulating strain of SARS-CoV-2 in the UK. We assess evidence of transmission, reinfection, and vaccine effectiveness. Our data show that the seven most common symptoms with Delta infection were the same as with Alpha infection. Risks of illness duration ≥7 days and ≥28 days, and of requiring hospital care, were not increased. In line with previous research, we found increased transmissibility of Delta vs. previous variants; and no evidence of increased re-infection rates. Our data support high vaccine efficacy of BNT162b2 and ChAdOx1 nCoV-19 formulations against Delta variant infection. Overall, our study adds quantitative information regarding meaningful clinical differences in COVID-19 due to Delta vs. other variants.Implications of all the available evidenceOur observational data confirm that COVID-19 disease in UK in adults is generally comparable to infection with the Alpha variant, including in elderly individuals. Our data contribute to epidemiological surveillance from the wider UK population and may capture information from COVID-19 presentation within the community that might be missed in healthcare-based surveillance. Our data may be useful in informing healthcare service planning, vaccination policies, and measures for social protection.

Protection against symptomatic infection with delta (B.1.617.2) and omicron (B.1.1.529) BA.1 and BA.2 SARS-CoV-2 variants after previous infection and vaccination in adolescents in England, August, 2021–March, 2022: a national, observational, test-negative, case-control study

“…There have been multiple waves of SARS-CoV-2 infections in the UK since March, 2020, with new waves often following the emergence and rapid spread of new variants, including the alpha (B.1.1.7) variant in November, 2020, delta (B.1.617.2) in April, 2021, and omicron (B.1.1.529) in November, 2021. Delta was more transmissible than alpha 7 but, unlike in adults, it was not associated with more severe disease in children and adolescents. 8 The ability of the omicron BA.1 variant, identified in England in late November, 2021, and the BA.2 variant, identified in late December, 2021, to evade both natural and vaccine-induced immunity was associated with the highest case numbers to date across all age groups, although hospitalisation rates and deaths remained low, 9 which was likely to be due to immunity from a combination of previous infections and vaccination, 10 and because the omicron variant infects the upper airway rather than the lower airway and causes less severe disease.…”

From Alpha to Delta—Genetic Epidemiology of SARS-CoV-2 (hCoV-19) in Southern Poland

“…It should be mentioned that Silesia is one of the most densely populated regions in Poland, which facilitates virus spread and may in part be responsible for the observed inequalities in the dynamic of B.1.617.2 lineage incidence. In the UK, B.1.617.2 rapidly became the dominant circulating SARS-CoV-2 variant, from 0.09% at the beginning of April 2021 to >98% at the end of June 2021, displacing the B.1.1.7 variant which concomitantly decreased from 98% to 1.67% [ 24 ]. These observations are in accordance with data collected in the GISAID database where the greater increase in sequences belonging to the B.1.617.2 lineage was reported in July and August [ 25 ].…”

The role of immune activation and antigen persistence in acute and long COVID

“…To date, there is limited data comparing the immunologic differences in COVID-19 based on the dominant variant at the time, especially with more recent variants such as Omicron. 54–63 Over time, SARS-CoV-2 has appeared to become less virulent while transmissibility has increased, although this is confounded by accumulated population immunity. 44,58,59,61,63–68 Even though SARS-CoV-2 can have a longer incubation period than some other respiratory viruses, viremia appears to peak at time of symptom onset.…”