Coronavirus outbreak: How do pandemics normally end?

Ever since the start of the coronavirus outbreak, people around the world have been asking the same question: how – and when – will the pandemic come to an end? If only there was a clear-cut answer.

Various measures have been taken across the globe to mitigate the impact of the virus. On 23 March, a nationwide lockdown was implemented across the UK, resulting in businesses closing their doors and members of the public being encouraged to stay at home as much as possible.

While the nationwide lockdown has since eased, local lockdowns have been put in place in certain regions across England. This later morphed into the government’s three-tier coronavirus restriction system, introduced in October, in a bid to categorise different postcodes according to virus risk.

Despite the public enduring these periods of lockdown, the evidence has shown that the outcome is not a long-term fix but a short-term one. Once society returned to greater levels of socialisation and schools and universities began again, the number of people hospitalised with Covid-19 returned to levels higher than when Britain first locked down in March.

As a result, it is reasonable to wonder whether we will remain stuck on this carousel of intermittent lockdowns until a vaccine is available; a scenario which experts, including chief medical officer Chris Witty and Kate Bingham, head of the vaccine task force, estimate could be another 12 months away. Can we look to the past, and other pandemics, to give us an alternative solution?

The most deadly pandemic in recent history was the H1N1 Spanish flu of 1918, which was estimated to have killed at least 50 million people worldwide over a two-year period till 1920. In 1957, the H2N2 influenza pandemic began, killing approximately one million people. The 1968 H3N2 flu pandemic came just over a decade later, resulting in a similar number of deaths. And 2009 marked the arrival of another flu pandemic, this time “swine flu”, which is estimated to have caused 284,000 deaths.

While lessons can be taken from past pandemics, it is important to note the majority were caused by strains of influenza, while Covid-19, a coronavirus, behaves quite differently from flu. Dr Nathalie MacDermott, NIHR (National Institute for Health Research) academic clinical lecturer at King’s College London, highlights this “unique” nature of Covid-19.

“This pandemic is actually quite unique, in the sense that we have a pathogen that is very capable of spreading. It’s highly infectious and highly transmissible, and it is infectious in individuals who are asymptomatic,” Dr MacDermott tells The Independent. “All of those factors make it much harder to contain than a lot of other epidemics that we might have experienced more recently.”

Dr MacDermott says if we, for example, look at the Ebola epidemic, which was not transmissible in people who were asymptomatic, this shows that it was easier to contain. “Even in the incubation period, which is about 21 days for Ebola, when people are technically infected but don’t have symptoms yet, they are not infectious to others,” she explains.

Despite Covid-19 having a distinct nature, which makes it harder to trace, are there still ways to emulate the successes of other pandemics drawing to a close? Many former pandemic-inducing diseases still circulate in the population today, including the bubonic plague, but as numbers are controlled, they are largely not a problem for wider society.

Dr Julian Tang, honorary associate professor in respiratory sciences and clinical virologist at the University of Leicester tells The Independent that is because the typical pattern of a pandemic is that it will “propagate through the whole population, because there’s no previous immunity, until that population’s all been infected and fully saturated, and then it normally dies off”.

The Spanish flu, for example, is said to have lasted between 1918-1920 when most people were dying, but that particular strain – H1N1 – actually remained in circulation for around 40 years, says Dr Tang. That is, until it was displaced by a new strain of influenza – H2N2 – causing a new pandemic to occur in 1957. Dr Tang says that academics are “still trying to understand” how a new virus is able to “replace the previous virus”, an occurrence that happens as the result of a “reassortment event”.

Fortunately the H2N2 strain was less lethal to humans, according to New Scientist, because the human-adapted H1N1 swapped genes with a H2N2 bird flu. The H1N1 virus, which also caused the 2009 swine flu pandemic, continues to circulate to this day, albeit posing less of a risk.

But this type of herd immunity exit has already been dismissed for Covid by academics as “unethical” and “unachievable”. This is because, like other illnesses, it seems that immunity to Covid-19 is short-lived. Dr Tang suggests antibodies could last between six to 12 months. “It will then reinfect those people who’ve actually cleared the virus,” he adds.

If herd immunity is not an option, then other courses of action include much discussed social measures, like distancing, mask wearing and an effective track and trace system. In fact, similar measures were carried out in the midst of the Spanish flu, in addition to being a key factor in the eradication of smallpox, Dr Tang states.

“Smallpox wasn’t eradicated just by the vaccine,” he says, in reference to the vaccine created by English doctor Edward Jenner in the late 18th century. “Smallpox was really eradicated by the track and trace, isolate and quarantine efforts, and then vaccinating all the contacts around them, so it was a combined effort.” In 1980, it was announced that smallpox had become the first and only infectious disease among humans to be completely eradicated.

Of course, international travel is a factor now when it comes to the spread of diseases, and the population size in 2020 is much greater than it was a century ago. But we also have much greater access to technology today, which can be utilised for measures like track and trace and generally improved standards of sanitation.

If these measures can sustain us until a vaccine arrives, will that be the end of Covid-19 and a return to life as we know it? There is the possibility that it will remain a part of our lives for a significant time. Comparisons can be drawn with the spread of HIV, described by the World Health Organisation as a “global epidemic”. In the US the first clinical observation of AIDS was made in 1981.

Christine Stegling, executive director of charity Frontline AIDS, points out that while antiretroviral medications are now available for people diagnosed as HIV positive, it remains an epidemic, with approximately 1.7 million new cases reported across the globe last year. Ms Stegling tells The Independent that while it is important not to make HIV and Covid-19 “compete with each other” when discussing the progression of either virus, the HIV epidemic may offer some guidance on how society can acclimatise to living with coronavirus, should a vaccine not become available in the near future.

Stegling adds that while some politicians describe Covid-19 as as “leveller” – a virus that “we’re all experiencing in the same way” – it may not necessarily be the case. She says: “Communities that are poorer or disadvantaged or marginalised in some way, with less food security and less income security, they are affected more than other communities. That’s a connection to HIV,” Ms Stegling says. “We’re quite interested to see what we can learn from HIV.”

Is there any chance that the virus might just burn itself out over time? Dr MacDermott explains that if the reproduction number (R nought) of the infection is reduced to below 1, “eventually the epidemic will usually burn itself out”. The aim would be to reach an R of “ideally quite a lot less than 1”, she states, adding that “if you’re sitting at 0.9, it’s going to take an awfully long time to get it under control”.

However, this has proven a challenge with Covid-19. As of Friday 16 October, the R rate in the UK ranged between 1.3 and 1.5, the British government outlined.

Despite humanity knowing more about coronavirus than in January, conversations are still plagued with uncertainties. Who knows if and when a viable vaccine will become available in the near future, and if it doesn’t, how long the pandemic will last? Past epidemics and pandemics show that it can take years for viruses to no longer pose a threat, with some remaining in circulation to the present day.