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expert reaction to latest batch of SAGE papers released on the B.1.617.2 variant and other VOCs

The latest batch of SAGE documents, published on Friday afternoon, provide more information on the B.1.617.2 variant and other VOCs.


Prof Sharon Peacock, Director of COG-UK, and Professor of Public Health and Microbiology, University of Cambridge, said:

“The latest SARS-CoV-2 data for England contains mixed news. An important positive is that B.1.351 (South Africa) and P1 (Brazil), variants that have worried us for months, have not gained ground (rates are not climbing). Similarly, E484K (associated with immune escape in B.1.351 and P.1) has emerged several times in B.1.1.7 but this has not led to an expansion of this specific variant. Looking back reinforces the fact that it is often only in retrospect that we know whether a given variant will prove to be a threat to COVID-19 control in England, but these particular variants are largely ‘sleeping threats’ at the moment. A precautionary approach with ongoing public health action and monitoring of them remains important.

“More concerning is the further jump in the number of people infected with B.1.617.2 in England (total confirmed cases have risen from 520 to 1313 in the last week). There are hotspots in London and the North West, but the variant is known to be present in numerous locations across the country. There have been new cases reported of B.1.617.1, but the increase is relatively smaller. At the same time, the proportion of cases due to B.1.1.7 are falling.

“An important question is how far B.1.617.2 has spread in England. Sequence data takes a week or more to become available but there are other ways to track variants.  Going back to the early days of B.1.1.7, so-called S gene target failure in specific 3-target PCR assays used in some Lighthouse labs was used to track the spread of B.1.1.7. Now, S gene positivity can be used to look for the reverse trend – replacement of B.1.1.7 by other variants (which are largely S gene positive). Caution is needed because of limited data, but for samples sequenced to date in May 2021 that were S gene positive, 93% were B.1.617.2. The latest PHE technical report shows that S gene positive samples are widespread across the UK and rising – in several regions of the country, there are now a greater proportion of S gene positive versus S gene negative samples. This is not definitive proof but is consistent with B.1.617.2 being widely distributed across the country. 

“All of this points to B.1.617.2 outcompeting other variants, including B.1.1.7 and other variants of concern. SPI-M-O is now confident that B.1.617.2 has a significant growth advantage over B.1.1.7, with a current estimate that B.1.617.2 has a transmission advantage of more than 50% over B.1.1.7. Given this, it is increasingly plausible that B.1.617.2 will go on to replace B.1.1.7 in England over time, in the same way that B.1.1.7 replaced other variants at the end of last year. Control measures through public health actions (testing, contact tracing, isolation) are very important since they slow the spread of even highly transmissible variants and buy us time. But everything we have learnt to date about B.1.1.7 indicates that these will not prevent a transmissible variant from national spread, and that highly transmissible variants have a biological passport for international travel and global spread.

“How will variant replacement manifest in England? Going back to our recent history with B.1.1.7, more transmission meant more B.1.1.7 cases compared with previous variants for the same control measures. Looking ahead to B.1.617.2, the same is likely to be true; for any given set of control measures, more B.1.617.2 cases should be expected versus the number of cases predicted for B.1.1.7. The latest SAGE papers provide early models on this.

“What that means in practice will depend on vaccine efficacy and the number of people vaccinated. There is no evidence at the moment that vaccines won’t work, but we don’t know enough yet because most laboratory data generated for this lineage is for B.1.617.1 rather than B.1.617.2 – and there are important genetic differences between the two. Urgent experimental data is being generated for B.1.617.2, as well as scrutiny of real-world data – in particular, rates of B.1.617.2 infection in people who have been vaccinated. We know that no vaccine is 100% effective and that vaccine breakthroughs will happen, but it will be important to compare the relative frequency of breakthrough in people infected with B.1.617.2 versus other variants to establish if the rates are the same or different. Also important is whether one vaccine dose is enough for this variant, or if two doses are needed.

“Vaccines have worked against all other variants to date and assuming that this is the case for B.1.617.2, we could anticipate a reduction is the number of infection cases overall compared with what would happen in an unvaccinated population, and a reduction in disease severity including the most severe manifestations of infection that require hospital admission and could result in death. Close attention is being paid to hospital admissions with COVID-19, and the proportion of mild versus severe cases. But infections of lesser severity remain important because of the risk of long covid.

“We don’t know enough yet about B.1.617.2 and disease severity. There is no evidence that B.1.617.2 causes more severe disease, but more data are needed to start to get a handle on this.”



Papers published by SAGE on Friday 14 May:

PHE: Investigation of SARS-CoV-2 variants of concern: routine variant data update, 13 May 2021

PHE: Investigation of novel SARS-CoV-2 variants of concern (England) – Technical briefing 11, 13 May 2021

SPI-M-O: Consensus statement on COVID-19, 12 May 2021

SAGE 89 minutes: Coronavirus (COVID-19) response, 13 May 2021



All our previous output on this subject can be seen at this weblink:



Declared interests

None received.

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