The coronavirus outbreak was first referred to as an epidemic, then a pandemic. Now, you might be hearing scientists describing Covid-19 as ‘endemic’ in the UK.
In late April, Professor Sarah Walker, an expert in medical statistics and epidemiology at Oxford and chief investigator for the Office for National Statistics (ONS) Covid-19 Infection Survey, said Britain had moved “from a pandemic to an endemic situation,” The Telegraph reported.
Her statement came as figures showed a huge drop in symptomatic Covid infections linked to the success of the vaccination programme.
Analysis of Covid test results taken from 373,402 study participants between December 2020 and April 2021 found that 21 days after a single dose, the rates of all new Covid-19 infections had dropped by 65%.
Meanwhile symptomatic infections had decreased by 74% and asymptomatic infections dropped by 57%. Reductions in infections and symptomatic infections were even greater after a second dose – 70% and 90% respectively.
What does endemic mean, then?
Where an epidemic refers to a disease that spreads rapidly within a community or region, a pandemic is an epidemic that has spread worldwide – crossing international boundaries and affecting a large number of people.
The definition of endemic is a disease that is native to, or commonly found within, an area. The suggestion here is that Covid-19 becomes endemic in the UK, like the flu – with recurring outbreaks but hopefully at lower levels.
Last year, experts from the World Health Organisation (WHO) suggested that Covid-19 was set to become endemic.
“The world has hoped for herd immunity, that somehow transmission would be decreased if enough persons were immune,” said Professor David Heymann, epidemiologist at the London School of Hygiene and Tropical Medicine, and chair of WHO’s strategic and technical advisory group for infectious hazards.
“It appears the destiny of SARS-CoV-2 is to become endemic, as have four other human coronaviruses, and that it will continue to mutate as it reproduces in human cells, especially in areas of more intense admission. Fortunately, we have tools to save lives, and these in combination with good public health will permit us to learn to live with Covid-19.”
Dr Michael Ryan, executive director of the WHO health emergencies programme, agreed: “The likely scenario is the virus will become another endemic virus that will remain somewhat of a threat, but a very low-level threat in the context of an effective global vaccination programme.”
What makes Covid-19 endemic?
In 2020, researchers Jeffrey Shaman and Marta Galanti, from Columbia Mailman School, identified key factors that would contribute to Covid-19 becoming endemic. These included: the risk of reinfection, how widely available (and effective) a vaccine is, as well as potential seasonality of the virus and interactions with other viral infections that may alter its transmission.
Their paper, published in the journal Science, explored a scenario where immunity to the virus diminishes within a year – a rate similar to another type of coronavirus that causes mild respiratory illness. At present, we know vaccine immunity lasts for at least six months.
If this were the case, there would be annual outbreaks of Covid-19, much like the flu, they said. But if immunity to the virus lasted longer, we might experience what seemed to be an initial elimination of Covid-19 followed by a resurgence after a few years.
Either way though, it’ll probably keep coming back – and with lots of new variants doing the rounds, that looks increasingly likely.
“Should reinfection prove commonplace, and barring a highly effective vaccine delivered to most of the world’s population, SARS-CoV-2 will likely settle into a pattern of endemicity,” the authors said.
“Whether reinfections will be commonplace, how often they will occur, how contagious re-infected individuals will be, and whether the risk of severe clinical outcomes changes with subsequent infection remain to be understood.”
Will Covid-19 ever disappear completely?
Total eradication of the virus is very unlikely, but not impossible. Smallpox, a virus that was very contagious and often deadly (three in every 10 people who got it died), was eradicated in 1980 thanks to vaccination programmes.
Professor Hans Heesterbeek, an expert in theoretical epidemiology at Utrecht University, in the Netherlands, wrote in a piece for The Conversation that if vaccines are found to prevent clinical disease, strongly reduce transmission and cause long-lasting immunity to Covid-19, eradication of the illness is possible.
“But realistically this is unlikely,” he said. “Eradication is notoriously difficult, even for diseases for which we have almost perfect vaccines and permanent immunity. Endemic disease is therefore the most likely outcome.”