With the spread of the delta variant, Covid-19 cases are hitting record highs in some areas of the United States and elsewhere in the world, health experts are revising how they believe the pandemic will continue to play out. Reporting for Bloomberg, Michelle Fay Cortez spoke to health experts about how Covid-19 compares to previous pandemics, what they think the next six months will look like—and how the pandemic will eventually come to an end.

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Covid-19 compared with pandemics of the past

Compared with the other pandemics of the past 130 years, the coronavirus pandemic is already shaping up to be among the most severe, according to Lone Simonsen, an epidemiologist and professor of population health sciences at Roskilde University in Denmark.

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The longest flu pandemic in the last 130 years lasted five years with two to four waves of infection over an average of about two to three years, Simonsen said. By comparison, the coronavirus pandemic is in its second year amid a third wave that has no end in sight, Cortez reports, and with more than 4.6 million Covid-19 deaths so far, the pandemic is already more than twice as deadly as any outbreak since the 1918 Spanish flu pandemic.

History has also shown that viruses don't necessarily get milder over time, Simonsen said. While new mutations aren't always worse than previous versions of a virus, "pandemics can in fact get more deadly during the pandemic period, as the virus is adapting to its new host," she said.

Coronaviruses have a "proof-reading" mechanism that fixes errors that occur when the virus replicates, making it less likely for variants to mutate when the virus is transmitted from person to person, Cortez reports. But because there are so many coronavirus infections, variants are popping up anyways.

"With the pandemic, we have this enormous force of infection," Kanta Subbarao, director of the WHO Collaborating Center for Reference and Research on Influenza at the Peter Doherty Institute for Infection and Immunity in Australia, said. "That has counterbalanced the ability of the virus to proof-read."

Because of this, it's possible Covid-19 could become endemic like the flu, potentially requiring regular vaccines to protect against the coronavirus as it evolves, Cortez reports.

Other research suggests the coronavirus may eventually become entirely resistant to the first generation of Covid-19 vaccines, Cortez reports. One pre-print study from Japan suggests that some potentially dangerous mutations within the delta variant are already being discovered; however, any reports that current strains of the virus cause higher fatality rates haven't yet been supported by research, Cortez reports.

What the next 6 months of the pandemic might look like

According to Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota and an adviser to President Joe Biden, Covid-19 surges are going to come and go over the next few months.

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"I see these continued surges occurring throughout the world," he said. "Then it will drop, potentially somewhat precipitously." Osterholm added that he then thinks "we very easily could see another surge in the fall and winter."

"We're going to see hills and valleys, at least for the next several years as we get more vaccine out. That's going to help. But the challenge is going to be: How big will the hills and valleys be, in terms of their distance?" Osterholm said. "We don't know. But I can tell you, this is a coronavirus forest fire that will not stop until it finds all the human wood that it can burn."

Some experts have said it's also possible a novel influenza virus could emerge in the coming months, or a different coronavirus could make the jump from animals to humans.

"As long as there are animal reservoirs of coronavirus there is still the possibility that another zoonotic coronavirus could emerge in the future," Subbarao said. "There is that in the background, the risk of still dealing with this one when another one emerges."

How will the pandemic end?

Generally speaking, experts agree the current Covid-19 surge will slow down once the majority of people have some level of immunization, whether from vaccines or prior infection, Cortez reports. The most important thing to do is get vaccinated, experts say.

"Without vaccination, one is like a sitting duck, because the virus will spread widely and find most everybody this autumn and winter," Simonsen said.

Going forward, it's likely the pandemic will end at different points in different places throughout the world, Erica Charters, associate professor of the history of medicine at Oxford University, said. Ultimately, local governments will have to determine how much Covid-19 they can live with, she added.

Some countries, such as Denmark and Singapore, have been able to keep Covid-19 cases somewhat muted and are already moving forward past the pandemic, while other countries, like the United States and the United Kingdom, are reopening despite significant Covid-19 surges.

"The end process is not going to be uniform," Charters said. The pandemic "is a biological phenomenon, but it's also a political and social phenomenon."

Ultimately, the end of the pandemic is likely to be complicated and will have a "lasting legacy" for many years, Cortez reports.

"We have to approach it with our eyes wide open and with a great deal of humility," Osterholm said. "Anybody [who] thinks we're going to be over this in the next few days or a few months is sorely mistaken." (Cortez, Bloomberg, 9/12)