What previous Covid-19 waves are now telling us about the virus – Community News
Covid-19

What previous Covid-19 waves are now telling us about the virus

After another brutal spike in coronavirus cases and deaths this summer — fueled by the Delta variant — infections in the United States are declining, 50 percent less than their September peak.

Experts say what comes next is hard to predict, and we often don’t know why the virus is spreading the way it is spreading. But looking back at the outbreak so far may provide some clues as to how the virus may spread in the future.


Average cases during phases of the pandemic


Average cases per 100,000 people

Summer 2020

June August

autumn 2020

September – November

Winter

December – February

spring 2021

March May

Summer and autumn 2021

June – 20 Oct


Note: Most Nebraska counties have not reported data for the summer of 2021.

The country is now going through five waves of the pandemic, depending on how you count. “Each of these waves has a different complexity and pattern,” said Alessandro Vespignani, the director of the Network Science Institute at Northeastern University in Boston.

For example, during the first wave, strict stay-at-home measures and drastic changes in behavior brought the virus to a halt for a while. Last fall, with those measures and behavior relatively relaxed, record-breaking waves in the Midwest swept south and both coasts. By the time the highly contagious Delta strain set off a wave across the country this summer, vaccines were widely available, once again changing the pattern.

“Vaccinations have clearly changed which places are affected and how much they are affected,” said Jennifer Nuzzo, an epidemiologist at Johns Hopkins University.

Below are five times the US case curve has peaked, and the lessons and insights experts have learned from each wave.

The first outbreaks






outbreaks in

meat processing facilities


outbreaks in

meat processing facilities


outbreaks in

meat processing facilities


In the spring of 2020, the first wave hit a few areas especially hard, including New York City, New Orleans and Albany, Georgia. Much came down to random chance as far as the virus struck first, experts said, though population density and transportation hubs may have played a role.

Tests were hard to come by during this time, so cases were drastically underreported. But death records show that the outbreak in the Northeast was one of the worst of the entire pandemic: One in about 400 New York City residents died within two months.

However, early home orders and widespread, drastic changes in behavior flattened the curve in those outbreaks, preventing the coronavirus from rippling across the country in waves, as it did at later peaks.

While hospitals in the Northeast Corridor flooded, nearby areas like Maine saw no major outbreaks. Isolated hotspots largely broke out in places where people couldn’t maintain social distancing, such as nursing homes, prisons and meat processing plants.

“I think it’s easy to miss how bad it could have been and how much better we’ve done than we could have, largely because of the lockdowns,” said Justin Lessler, a professor of epidemiology at the University of North Carolina.

Hotspots in the Sun Belt





Outbreaks on

native American

reservations

Outbreaks on

native American

reservations


In the summer of 2020, cases increased again, but this time Sun Belt states experienced the worst outbreaks. Many states that set new records for cases and deaths were also the first to reopen, including South Carolina, Alabama, Georgia, and Mississippi. Experts say seasonality — perhaps the summer heat of the Sun Belt driving people in — may also have been a factor.

The summer wave hit many metropolitan areas of the South and Southwest, including Houston, Miami and Phoenix. Without strict virus restrictions, the virus spread to suburbs and suburbs. By the end of the summer, most of the worst outbreaks occurred in rural areas.

“If you think about the spring wave in 2020, it was more pointed around urban areas. In the other waves, you see more of a general flow,” said Dr. Vespignani, “like when you throw a rock into a pond.”

The winter wave


The flow of cases is more apparent in the wave that began in the Upper Midwest in September 2020. North and South Dakota had few virus restrictions to contain an outbreak, and both states had particularly bad spikes. One in 10 residents tested positive for the virus in North Dakota in the fall, and experts think many more cases went undetected.

From there, the outbreak spread beyond the Midwest, reaching both coasts and stretching south in a devastating wave. The country saw more daily cases and deaths in January than any time before or since.

“You see this movement, almost like it’s moving from province to province,” said Jeffrey Shaman, an infectious disease epidemiologist at Columbia University, who said researchers found that community-to-community transmission played an important role in virus spread during the H1N1 2009. pandemic. But dr. Shaman said factors other than proximity could also have played an important role in Covid.

Different communities may have similar school opening dates, for example experiencing the same cold fronts or sharing similar patterns of behavior, all of which can lead to independent outbreaks at the same time.

“If you look at anything after October last year, the virus is everywhere. It didn’t need to be reintroduced,” said Dr. Shaman.

Then, in community after community, cases often declined as quickly as they had risen. A sharp drop after a peak is not uncommon during epidemics, experts say. When a virus quickly spreads through a community, it eventually runs out of people to infect.

A mystery in Michigan


By the spring of 2021, cases in the US had receded far from their winter peak. At the same time, a more contagious strain that had caused a huge surge in the United Kingdom, called Alpha, quickly became dominant in the United States.

Michigan saw a large increase in cases and deaths, causing experts to worry that the variant would trigger a similar nationwide outbreak. Instead, the virus appeared to stop at the Michigan border in May.

Epidemiologists still don’t know why Michigan was unlucky — or why the outbreak didn’t spread to neighboring states. But some noted that it happened around the time all adults first became eligible for the vaccine, and before social distancing behavior eased significantly.

It’s possible that people became more cautious during the revival, slowing the spread, said Dr. Lessler, the epidemiologist at the University of North Carolina. Then vaccines helped eradicate it.

Delta’s Devastation





Case and death certificates

broken over the south

Case and death certificates

broken over the south


By June, US coronavirus cases were at an all-time low since the start of the pandemic, and nearly half the population had received at least one shot. States have lifted virtually all virus restrictions and people relaxed their behavior in celebration.

The timing proved disastrous, especially for areas with lower vaccination coverage. Another variant, this time Delta, gained a foothold and quickly grew into a majority of US cases. Missouri saw the first major wave of the Delta Wave.

“There the fire was kindled; then the fire started to spread to other places,” said Dr. Vespignani.

Soon that outbreak spread across Arkansas and then to Louisiana, both states with low vaccination coverage. Florida became another early Delta hotspot. By the end of August, most states in the South had set new records for daily cases or deaths, and the virus turned north, causing spikes in the upper Midwest and the Mountain West.

While the Delta Wave rolled over much of the country, some places were relatively spared.

“That fire, for example, never made it to the northeast corridor,” said Dr Vespignani. “It is where there is one of the highest vaccination rates. It’s like there’s a wall.”

Some experts say the vaccination campaign and much of the country, which has already experienced several waves of outbreaks – which have provided some immunity to those infected and recovered – have made them cautiously optimistic for the winter.

dr. Lessler, who helps run the Covid-19 Scenario Modeling Hub, a consortium of research groups that model the future of the outbreak, said none of the groups predicted a substantial winter peak in the United States this year.

“We can see a little bump in some cases, and of course people can radically change their behavior or we can see a variant,” said Dr. Lessler, but he added that he didn’t think a substantial spike was likely.

Still, there will undoubtedly remain places where the virus can spread, as each new wave has shown. And questions still remain about how long the immunity will last.

“The difference between the Michigan Alpha wave in the spring of 2021 and the Delta wave really tells you that the wall you’ve built may work for one variant, but it may not be enough for the next,” said Mr. Vespignani. “There may be another variant that is more transmissible and has more immune evasion. That’s why we need to build the wall as high as possible.”