#16,009
Despite being well off its massively high daily case counts of just a few months ago - since early May the UK has seen a gradual tripling of daily COVID cases - as the Delta (B.1.617.2) variant becomes increasingly entrenched (see BBC Covid-19: Delta variant makes up 91% of new UK cases).
Each Friday the UK's PHE (Public Health England) releases a trove of new data and analysis, usually including a new risk analysis on the COVID variant of great concern (currently B.1.617.2), and a detailed technical briefing.
We've excerpts from three updates this morning; the latest Technical Briefing (#15), a revised Risk Assessment on the Delta variant, and a PHE Study showing increased household transmission of the Delta Variant (compared to B.1.1.7).
First stop, the largest (77-page PDF), and most detailed document of this week's data dump; the UK's latest technical briefing. Given its size, we'll only look at the summary. Follow the link to read it in its entirety.
SARS-CoV-2 variants of concern and variants under investigation in England
Technical briefing 15
11 June 2021Summary
There are 4 variants of concern and 8 variants under investigation (Table 1).
This report has been published to continue to share detailed surveillance of Delta (VOC21APR-02, B.1.617.2). A separate report is published covering our routine data on all other variants of concern and variants under investigation. These additional specialist technical briefings represent early data and analysis on an emerging variant and findings have a high level of uncertainty.
Principal changes and findings this week are:
- for the first time this week, published figures include genotyping assay data, using a highly specific mutation as an indicator of a probable Delta variant case
- the most recent data show 74% of sequenced cases and 96% of sequenced and genotyped cases are Delta.
- the 28-day case fatality rate for Delta remains low (0.1%), though mortality is a lagged indicator and the vast majority of cases are still within the 28 days of follow-up required.
- secondary attack rates have been iterated and remain higher for Delta than Alpha in both traveller and non-traveller cases and amongst both household and non-household contacts
- early data from both England and Scotland demonstrate an increased risk of hospitalisation with Delta compared to Alpha
- the majority of outbreaks managed by health protection teams and exposure settings identified through contact tracing are attributed to Delta variant
The risk assessment for Delta is published separately and has been updated this week.
As Delta is now the dominant variant in the UK, from next week epidemiological data will be presented in the PHE Weekly Surveillance report and the technical report will focus on new data that informs the risk assessment.
The PHE has also published a new revised risk assessment, which once again ups the ante on increased transmissibility, infection severity, and reduced vaccine effectiveness - albeit in the case of increased severity, with low confidence levels.
The $64 question remains - how effective will current vaccines be in protecting against this highly transmissible variant? - and on that point, the jury is still out. The UK's latest assessment states:
Epidemiological and laboratory evidence of reduced vaccine effectiveness
There are now analyses from England and Scotland supporting a reduction in vaccine effectiveness for Delta compared to Alpha. This is more pronounced after one dose (absolute reduction in vaccine effectiveness against symptomatic infection of approximately 15% to 20% after 1 dose). Iterated analysis continues to show vaccine effectiveness against Delta is higher after 2 doses but that there is a reduction for Delta compared to Alpha.
There is uncertainty around the magnitude of the change in vaccine effectiveness after 2 doses of Oxford-AstraZeneca vaccine. Although this is observational data subject to some biases, it holds true across several analytic approaches and the same effect is seen in both English and Scottish data. It is strongly supported by pseudovirus and live virus neutralisation data from multiple laboratories. There are no data on whether prevention of transmission is affected. The analysis of vaccine effectiveness against hospitalisation is in process. The acquisition of the mutation K417N, which may be antigenically significant, in a small number of cases is noted.
The overall assessment now reads:
Delta is predominant and all analyses find that it has a very substantial growth advantage. The observed high growth rate is likely to be due to a combination of transmissibility and immune escape; there is still geographic heterogeneity and a probable contribution from place-based context. Iterated analyses this week continue to support our previous estimates of vaccine effectiveness and hospitalisation risk.
The priority investigations are vaccine effectiveness against hospitalisation and death, further investigations of secondary attack rates, characterisation of the generation time, viral load and period of infectivity, and epidemiological studies of reinfections.
Our last stop is a new study, released this week by the PHE, on household transmission of the Delta variant (compared to Alpha), that finds the Delta variant has a 64% advantage. Some excerpts from the paper follow, but click the link to read it in its entirety.
Authors Hester Allen*, MSc, Amoolya Vusirikala*, MFPH, Joe Flannagan, MSc, Katherine A. Twohig, MPH, Asad Zaidi, MSc, COG-UK Consortium, Natalie Groves, MSc, Jamie Lopez-Bernal, FFPH, Ross Harris, PhD, Andre Charlett, PhD, Gavin Dabrera, FFPH, Meaghan Kall, MPH
Summary
Background The SARS-CoV-2 B.1.617.2 variant (Delta) first detected in India, has rapidly become the dominant variant in England. Studies suggest this variant has increased growth rate and is more transmissible than the previous dominant B.1.1.7 (Alpha) strain. This study aimed to assess the difference in transmissibility in England between the emergent B.1.617.2 variant compared to B.1.1.7 variant.
Methods A matched case-control study was conducted to estimate the odds of household transmission for B.1.617.2 index cases compared with B.1.1.7 SARS-CoV-2 index cases. Two-to-one matching was undertaken on the basis of geographical location of residence, time period of testing and property type, using a conditional logistic regression model.
Findings 3,765 genomically sequenced index cases in household clusters (≥ 2 cases in a household), were matched to 7,530 sporadic cases (single cases in a household). 5.8% (n=220) of index cases in household clusters had confirmed B.1.617.2 variant, compared to 4.7% (n= 351) of sporadic cases. The adjusted odds of household transmission was 1.64 among index cases with B.1.617.2 variant (95%CI 1.26 to 2.13, p <0.001) compared to the B.1.1.7 variant after adjusting for age, sex, ethnicity, index of multiple deprivation (IMD) and vaccination status of index case.
Interpretation Overall, we found increased household transmission of COVID-19 associated with B.1.617.2 compared to B.1.1.7. These findings show households are important settings for rapid transmission of the lineage B.1.617.2. With household settings being an important factor in wider community spread, strategies to prevent transmission in these settings are vital to control the COVID-19 pandemic.
(SNIP)
Discussion This study found a 64% increase in the odds of household transmission associated with infection with B.1.617.2 SARS-CoV-2 variant compared to B.1.1.7, following adjustment for the index cases’ vaccination status, as well as sex, ethnicity, IMD and age group.
This study provides early real-world evidence of the effect B.1.617.2 variant on household transmission. The findings support existing evidence that B.1.617.2 has a substantially increased transmissibility advantage over the B.1.1.7 variant which has contributed to the rapid increase in the number of B.1.617.2 cases in the UK over the study period and the level of increase is consistent with estimates of increased transmission to close contacts (2, 4, 9).
This study also found evidence of increased household transmission among households with an index case of Asian ethnicity, a finding which is consistent with studies of the previously dominant B.1.1.7 variant (10). These results add important new evidence to help understand the underlying reasons for this increased susceptibility to COVID-19 infection, and possibly reflect differences in household composition and inter-household mixing between ethnic groups, such as more common large or multi-generational households.
While the Delta variant currently makes up a tiny percentage of U.S. cases, it is growing at three times the rate of competing variants (see CDC U.S. Variant Update: B.1.1.7 Still Dominant But P.1 & B.1.617.2 Continue To Rise), and stands a very good chance of becoming dominant here in the months ahead.
The UK, unfortunately, finds itself a bit of a trailblazer when it comes to the Delta variant. Hopefully, what we learn from the UK's experience with B.1.617.2 may help us navigate this next phase of our pandemic more effectively.
