Dr Muiris Houston: ‘Endemic good, pandemic bad?’

As hopes rise that we may be nearing the end of the Covid-19 pandemic, the inevitable question arises: what comes next? Will the Sars-CoV-2 virus fade away to become a distant bad memory? Could a new variant trigger another global pandemic? Or does the rate of novel coronavirus infection become static, with no waves or surges – the epidemiological definition of endemic?

The probability of endemic Covid-19 has been largely welcomed in the media. It’s part of a rosy misconception that viruses evolve over time to become more benign. It places Covid-19 in the relative comfort zone of viruses that cause the common cold and influenza.

But there is no predestined evolutionary outcome for a virus to become more benign, especially ones, such as Sars-CoV-2, in which most transmission happens before the virus causes severe disease. Remember, the Alpha and Delta variants are more virulent than the strain first found in Wuhan, China. And the second wave of the 1918 influenza pandemic was far more deadly than the first.

Choosing a future of pandemic/epidemic/endemic for Covid-19 seems as random as the choice in Rock/Paper/Scissors

So a disease can become endemic and yet remain widespread and deadly. Malaria killed more than 600,000 people in 2020. Ten million developed tuberculosis and 1.5 million died in the same year.

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Writing in the journal Nature, Oxford University evolutionary virologist Aris Katzourakis says: "Stating that an infection will become endemic says nothing about how long it might take to reach stasis, what the case rates, morbidity levels or death rates will be or, crucially, how much of a population – and which sectors – will be susceptible.

“Health policies and individual behaviour will determine what form – out of many possibilities – endemic Covid-19 takes.”

I suspect that for many of us the term endemic softens to become, “this virus is done and dusted, let’s move on.” According to Dr Raywat Deonandan, an epidemiologist at the University of Ottawa, Canada, when people say “endemic,” they often mean they want to see Covid-19 brought under control.That’s the point when a disease “pesters us all the time but we have a handle on it,” he says.

An endemic level of immunity is achieved through a combination of vaccination and recovery after natural infection. However, some people will still get sick with Covid-19, especially those who are particularly vulnerable. For example older people, young children and those who are immunocompromised are at higher risk of becoming seriously ill with the flu and need to be protected by annual vaccination. We are likely to see a similar situation when SARS-CoV-2 becomes endemic.

At present, choosing a future of pandemic/epidemic/endemic for Covid-19 seems as random as the choice in Rock/Paper/Scissors. So is there anything we can do to get to an endemic state more quickly?

There is one intervention that will speed our journey: ensure significantly more people in all countries are vaccinated. We cannot solve a global problem locally. The best way to prevent more-dangerous or more-transmissible variants from emerging is to stop unconstrained spread, and that requires vaccine equity.

Here is Prof Katsourakis’ recipe for progress: “First, we must set aside lazy optimism. Second, we must be realistic about the likely levels of death, disability and sickness. Targets set for reduction should consider that circulating virus risks giving rise to new variants. Third, we must use – globally – the formidable weapons available: effective vaccines, antiviral medications, diagnostic tests and a better understanding of how to stop an airborne virus through mask wearing, distancing, and air ventilation and filtration. Fourth, we must invest in vaccines that protect against a broader range of variants.”

There is an absolute scientific truth in what he says. But I suspect many of us would quickly accept a looser, lay-persons’ brand of endemicity, involving annual Covid-19 jabs and the judicious use of masks and hand hygiene. I know I would.

[ mhouston@irishtimes.com ]