[LINK] How does Covid end?

[Stephen Loosley]

How does Covid end?

‘Letting the virus rip, even in a highly vaccinated population, carries risks.’

By Laura Spinney Fri 29 Oct 2021 https://www.theguardian.com/commentisfree/2021/oct/29/how-does-covid-end-uk-virus-endemic

Covid-19 has been described as a dress rehearsal for our ability to solve the bigger problem of the climate crisis, so it seems important to point out that the pandemic isn’t over.

The endgame has been obvious for a while: rather than getting rid of Covid-19 entirely, countries will get used to it.

The technical word for a disease that we’re obliged to host indefinitely is “endemic”. It means that the disease-causing agent – the Sars-CoV-2 virus in this case – is always circulating in the population, causing periodic but more-or-less predictable disease outbreaks.

The virus won’t disappear – it will just become endemic. But it could still put pressure on health systems in years to come

No country has entered the calmer waters of endemicity yet; we’re all still on the white-knuckle ride of the pandemic phase.

In the pandemic phase, outbreaks are unpredictable and bad. There are simply too many people who remain susceptible to the virus, either because they’re unvaccinated or because they haven’t yet encountered the now-dominant Delta variant, which transmits even among the fully vaccinated.

The virus will find most of them eventually – even if it does not cause them all to become seriously ill.

Only when such pools of susceptibility have dried up can we say the pandemic is over, the infectious disease modeller Adam Kucharski of the London School of Hygiene & Tropical Medicine told me. From then on, the disease’s spread will be sustained by gentler forces such as the gradual waning of immunity in the human population, and the emergence of relatively mild new variants.

But nobody knows yet when that will happen, because there’s uncertainty about how long a person remains immune to Sars-CoV-2 following natural infection or vaccination, and about the virus’s capacity to generate variants that aren’t mild.

One thing is clear: the transition to endemicity will happen at different times in different countries and regions. It’s not unreasonable to think that the UK, with its high case numbers and vaccination rates, might be among those closest to the tipping point – which is why other countries are watching it closely.

Delta, which is around three times as transmissible as the original Wuhan variant of Sars-CoV-2, has yet to reach many countries, but since May it has been dominant in the UK, where it has spread like wildfire since “freedom day” on 19 July. That’s why some scientists think the UK is entering its final pandemic wave, from which it will exit into the endemic phase next spring.

Others think the pandemic has several more waves left in it, even in the UK. The waves may be smaller than in the past, especially since vaccines have broken the link between infection and hospitalisation to a large degree.

But Britons may still be facing another year or more during which vulnerable people die in large numbers, others report the debilitating effects of long Covid, and health systems creak and potentially crack under the strain.

Every country will eventually reach endemicity, but the UK is heading there very fast – and there will inevitably be a human toll to pay. Letting the virus rip, even in a highly vaccinated population, carries other risks too.

“The high case numbers in the UK at the moment can only increase the risk of emergence of variants of concern,” the modeller Robin Thompson of the University of Warwick told me.

We have yet to see a Covid variant that causes severe disease even in the fully vaccinated. Touch wood, we won’t.

Virologist Didier Trono of the Ecole Polytechnique Fédérale de Lausanne in Switzerland is cautiously optimistic that SARSars-CoV-2 is nearing the limits of its capacity to adapt.

Though new variants continue to emerge – such as AY.4.2, which recently started spreading in the UK – these have only been slightly more transmissible than Delta, at most, and the disease is not dramatically more severe now than it was in early 2020.

But as immunity grows in the population, so does the selective pressure for the virus to mutate and escape that immunity. Vaccinologists are working hard to prepare for this risk.

It’s a race to the finish, in other words, but a race that might not be won by the fastest. At this point, vaccines are protecting us individually, not collectively. But the form that the endemic disease will take will be shaped collectively.

The future of Covid-19 could be as mild as a common cold, but it could be worse. The response to this future disease may need to be more onerous than the response to flu, which involves only an annual vaccination campaign.

“I don’t think we can rule out a situation where Covid, though endemic, puts overwhelming pressure on health systems in some years,” Kucharski told me.

That’s why the pandemic is still very much a collective action problem, and why the coming wave – whether or not it’s the exit wave – should be met with masks, other light social distancing measures where and when required, and a high uptake of booster shots among those who are eligible.

The strategy has to remain as nimble as the virus, which also means ensuring that there is no trade-off between booster campaigns in wealthy countries and the rollout of initial vaccine doses in poorer ones.

Sars-CoV-2 may have been cornered, but it hasn’t been tamed; it still has plenty of bite in it.

Laura Spinney is a science journalist and the author of Pale Rider: The Spanish Flu of 1918 and How it Changed the World