New data released over the weekend added to concerns about the ability of the Covid variant first detected in India – B.1.617.2 – to spread in the UK, but brought relief by suggesting that the vaccines still offer considerable protection against this growing threat.
With many still not eligible for vaccines or partially vaccinated, what does this mean for the government’s roadmap out of restrictions?
What do we know about the transmissibility of the India variant?
Data shows that B.1.617.2 has continued to replace B.1.1.7, the so-called Kent variant that became dominant in the UK last year – and in some places by a considerable margin. In the two weeks to 15 May, the variant accounted for 81% of analysed samples in Bedford, 90.4% in Blackburn and 64% in Wigan, according to the Wellcome Sanger Institute’s Covid-19 genomic surveillance data, which excludes recent travellers and surge-testing specimens.
Public Health England (PHE) data on the likelihood that a close contact of a person infected with B.1.617.2 will get infected themselves – the “secondary attack rate” – is 12.5%, compared with 8.1% for the Kent variant, which is more than 50% higher. This is good evidence that the India variant is substantially more transmissible than B.1.1.7, said Martin McKee, professor of European public health at the London School of Hygiene & Tropical Medicine, cautioning that these numbers have not yet accounted for vaccination status.
It could be that the secondary attack rate reduces when contacts are stratified by vaccine status or by whether they are within or outside the household, said Adam Kucharski, an associate professor at the London School of Hygiene & Tropical Medicine. “So, it might be the real number is a bit lower when you adjust for the fact that some of those contacts might be more or less risky than others. But I think as a ballpark, that is a clear early signal and I think we have to pay attention to it.”
How effective are the vaccines?
A preliminary PHE analysis showed that three weeks after one dose, both the Pfizer/BioNTech and Oxford/AstraZeneca vaccines saw a drop in effectiveness against symptomatic disease to roughly 33.5% against the India variant, versus about 51% for the Kent variant. After two doses, the Pfizer/BioNTech jab had an effectiveness of about 88% against the India variant, compared with 93.4% against the Kent variant. With the Oxford/AstraZeneca vaccine, the numbers fell to roughly 60% and 66%. (These differences in effectiveness are likely to change as more data is collected – because the second doses of Oxford/AstraZeneca vaccine were deployed later than the Pfizer/BioNTech vaccine, and data shows it takes longer to reach maximum effectiveness with the Oxford/AstraZeneca vaccine.)
With the ability to spread faster and a minimum three-month lag between vaccine doses among the under-50’s, the virus has an opportunity to get a foothold because so many people in that age range are partially or are yet to be vaccinated, said Dr Stephen Griffin, an associate professor at the University of Leeds school of medicine.
“I think the major issue is the time it takes for the optimal response which means that we really need to get the second doses into people as quickly as possible. That could mean that you prioritise people for a three-week Pfizer or Moderna protocol in those areas, I think that would be sensible. Because it’s not that AstraZeneca is a bad vaccine – it’s just for the optimal response you need that longer lag.”
What does that mean for the coming months?
Minutes taken at meetings of the UK government’s Scientific Advisory Group for Emergencies (Sage) showed the scientists expected that a variant that substantially escapes immunity or is highly transmissible (more so than the Kent variant) could lead to a wave of infections – potentially larger than that seen in January 2021 – in the absence of interventions.
The recent rise in case numbers of the India variant and the dramatic fall in cases of the Kent variant will continue and get more intense in the coming weeks, given that we are yet to see the impact of the third stage of lockdown-easing, which lifted a range of restrictions on 17 May, said Paul Hunter, a professor in medicine at the University of East Anglia.
“The big uncertainty is if the vaccination campaign that we’ve got is enough to keep people out of the hospital even if they get infected. And if that holds, then we might end up seeing the infection circulating widely in the community, but not imposing unbearable pressures on the health system – not leading to a huge increase in fatalities.”
Globally, it appears that hospitals are not exclusively filling up with elderly people – there are a lot of middle-aged people, particularly in areas of high transmission, Kucharski added.
“I think we are in this period, particularly over the next couple of months, where we have a lot of people who have got partial protection – and if you have got low case numbers that will probably be enough. But if you had very high case numbers, even if it is quite a small risk, at a population level that can still translate up into quite a lot of hospitalisations.”
Given that most cases of B.1.617.2 are a result of community transmission, and that the unlocking continues with a virus that is better able to spread exponentially, there could be a lot of illness, said Griffin. “We need to learn the lessons that we need to be proactive and preventive, because being reactive just doesn’t work.”
