Health

How will COVID end? Experts look to past epidemics for clues

Two years after the onset of the COVID-19 pandemic, much of the world has seen dramatic improvements in infection rates, hospitalizations and deaths in recent weeks, indicating that the crisis appears to be waning. But how will it end? Past epidemics may provide clues.

The end of epidemics has not been studied as thoroughly as their beginning. But there are recurring themes from which lessons can be learned in the coming months, says Erica Charters of the University of Oxford, who studies the issue.

“One thing we’ve learned is that it’s a long, drawn out process” that involves different types of endings that can’t all happen at the same time, she said. This includes a “medical end” when the disease recedes, a “political end” when government preventive measures end, and a “social end” when people leave.

The global COVID-19 pandemic has evolved and receded in different ways in different parts of the world. But at least in the United States, there is reason to believe that the end is near.

About 65% of Americans are fully vaccinated, and about 29% are vaccinated and revaccinated. The incidence has been declining for almost two months, with the US daily average dropping by about 40% in the last week alone. Hospitalizations also fell sharply, by almost 30%. Mask mandates are fading – even federal health officials have stopped wearing them – and President Joe Biden has said it’s time for people to return to offices and many aspects of pre-pandemic life.

But this pandemic was full of surprises, lasting for more than two years and killing almost 1 million people in the US and more than 6 million people worldwide. Its severity was unexpected, in part because many people learned the wrong lesson from the 2009-2010 flu pandemic, which turned out to be nowhere near as deadly as originally feared.

“We were all worried, but then nothing happened [in 2009]and I think that’s what was expected” when COVID-19 first emerged, said Christine Heitman, a Maryland researcher who collaborated with Charters.

However, some experts have offered insights from past epidemics that could provide insight into how the end of the COVID-19 pandemic might play out.

Flu

Prior to the advent of COVID-19, influenza was considered the deadliest pandemic agent. Historians estimate that the 1918-1919 influenza pandemic killed 50 million people worldwide, including 675,000 in the United States. Another influenza pandemic in 1957–1958 killed an estimated 116,000 Americans, and another in 1968 killed another 100,000 people.

A new flu in 2009 caused another pandemic, but it was not particularly dangerous for older people – the group most likely to die from the flu and its complications. Ultimately, fewer than 13,000 deaths in the US are linked to this pandemic.

The World Health Organization announced in August 2010 that influenza had entered the post-pandemic period, with cases and outbreaks becoming seasonal.

In each case, the pandemics weakened over time, and immunity developed in the general population. They became the seasonal flu of subsequent years. Experts say the same pattern is likely to occur with the coronavirus.

“It’s becoming normal,” said Matthew Ferrari, director of the Center for Infectious Disease Dynamics at the University of Pennsylvania. “There is a regular undulating pattern where there are times of the year when there are more cases and times of the year when there are fewer cases. Something that will be very similar to the seasonal flu or cold.”

HIV

In 1981, US health officials reported a cluster of cases of cancerous lesions and pneumonia in previously healthy gay men in California and New York. More and more cases began to appear, and by the next year, officials were calling the disease AIDS from Acquired Immune Deficiency Syndrome.

Researchers later determined that it was caused by HIV, the human immunodeficiency virus, which weakens the human immune system by destroying disease and infection-fighting cells. For years, AIDS was considered a horrendous death sentence, and in 1994 it became the leading cause of death for Americans aged 25 to 44.

But treatments that became available in the 1990s turned it into a manageable chronic condition for most Americans. Attention shifted to Africa and other parts of the world where it was out of control and is still considered an ongoing emergency.

Pandemics don’t end with a uniform decline in cases around the world, Charters said. “A pandemic usually ends up becoming multiple [regional] epidemic,” she said.

Zika

In 2015, Brazil experienced an outbreak of Zika virus infection, which is spread by mosquitoes that typically cause only mild illness in most adults and children. But it became a horror when it was discovered that an infection during pregnancy could cause a birth defect that affects brain development, causing babies to be born with unusually small heads.

By the end of that year, mosquitoes had spread it to other countries in Latin America. In 2016, the WHO declared it an international public health emergency, and the influence of the US became apparent. The Centers for Disease Control and Prevention has received reports of 224 cases of Zika virus transmission by mosquitoes in the continental United States and more than 36,000 cases in US territories, the vast majority of which are in Puerto Rico.

But rates plummeted in 2017 and all but disappeared shortly thereafter, at least in the US. Experts believe that the epidemic stopped when people developed immunity. “He just kind of burned out,” and pressure to make a Zika vaccine available in the US eased, said Dr. Denise Jamison, a former CDC staffer who was a key lead in the agency’s response to Zika.

The Zika virus may be a latent problem for many years, but outbreaks could recur if the virus mutates or if more young people without immunity emerge. Most epidemics “never have a hard end,” said Jamison, who now chairs the department of gynecology and obstetrics at Emory University School of Medicine.

COVID-19

The WHO declared COVID-19 a pandemic on March 11, 2020, and it will decide when there has been enough decline in cases in enough countries, or at least in hospitalizations and deaths, to say that the international health emergency is over.

WHO has not yet announced target thresholds. But officials this week answered questions about a possible end to the pandemic, noting how much more needs to be done before the world can turn the page.

Cases of COVID-19 in the US are on the decline and have fallen by 5% globally over the past week. But cases are on the rise in some places, including the UK, New Zealand and Hong Kong.

People in many countries need vaccines and medicines, said Dr. Carissa Etienne, director of the WHO’s Pan American Health Organization.

In Latin America and the Caribbean alone, more than 248 million people have yet to receive their first dose of the COVID-19 vaccine, Etienne told a news briefing. Countries with low vaccination rates are likely to experience an increase in infections, hospitalizations and deaths in the future, she said.

“We are not yet out of this pandemic,” said Dr Ciro Ugarte, PAHO Director of Health Emergencies. “We still need to approach this pandemic with great caution.”

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The Associated Press Department of Health and Science receives support from the Howard Hughes Medical Institute Department of Science Education. AP is solely responsible for all content.


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