Previous waves were ‘relatively small’ – why modelers are worried about the Indian variant


It was classified as a ‘variant of concern’ because it ticks the first box – scientists are now almost certain that it has some transmission advantage. There is also laboratory evidence suggesting that it can dilute immunity, but not catastrophically. A full vaccination (two doses) will provide protection against serious illness if the experience of healthcare workers in India is anything to say, experts say. Finally, on the virulence of the variant – its lethality compared to existing spots – there is so far no evidence to cause concern.

So why worry about the speed of travel of the variant when around 69% of the population now have anti-Covid antibodies, rising to over 90% among the most vulnerable? What damage could it cause given these levels of population immunity?

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It’s this question that bothers almost everyone, but the answer comes down to simple, albeit counterintuitive, math. Professor Adam Kucharski, one of Sage’s modellers from the London School of Hygiene and Tropical Medicine, explains it as follows: “The problem is that a lot of people have a mental image that we do. [already] had the biggest outbreaks possible, when we actually had relatively small ones compared to what could have happened without the control measures in place.

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“As a result of these checks, only a fraction of the people who could have been infected in the past year have been infected, so they are still there.

“Of course, for many of these people, vaccines have now significantly reduced their risk. But a very large number of infections that come with a very small level of individual risk can produce a similar outcome to a smaller epidemic that carries a higher level of individual risk ”.

And that’s exactly what Sage modeling shows (see graphics below). If the new variant is only 10-20% more transmissible, we will only see a slight increase in new hospitalizations. But if it is 30 to 50% more transmissible, the number of infections becomes so large that hospitalizations are rapidly skyrocketing beyond the NHS ‘ability to cope.

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“At this point in the vaccine rollout, there are still too few adults vaccinated to prevent a significant resurgence that could ultimately put unsustainable pressure on the NHS, without non-pharmaceutical interventions,” Sage’s briefing tells the Prime Minister .

“Yes [the Indian variant] has such a great advantage in terms of transmission, it is realistic to think that progressing through all the stages of the roadmap would lead to a substantial resurgence of hospitalizations ”.