What Previous Covid-19 Waves Tell Us About the Virus Now - The New York Times

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

Experts say what comes next is hard to predict, and we often do not know why the virus spreads the way it does.

But looking back at the outbreak so far can provide some clues about how the virus may spread in the future.

“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.

During the first wave, for instance, strict stay-at-home measures and drastic changes in behavior may have stalled the virus for a time.

By the time the highly contagious Delta variant fueled a wave across the country this summer, vaccines were widely available, shifting the pattern once again.

case curve hit a peak, and the lessons and insights experts have gleaned from each wave.

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In the spring of 2020, the first wave hit a few areas particularly hard, including New York City, New Orleans and Albany, Ga.

A lot came down to random chance insofar as where the virus struck first, experts said, though population density and transportation hubs may have played a role.

But death data indicates the Northeast’s outbreak was one of the worst of the whole pandemic — one in about 400 New York City residents died within the span of two months.

Many states that set new records for cases and deaths were also those that reopened first, including South Carolina, Alabama, Georgia and Mississippi.

Without tight virus restrictions in place, the virus spread outward into suburbs and exurbs.

Vespignani said, “Like when you throw a stone in a pond.”.

North and South Dakota had few virus restrictions in place to contain an outbreak, and both states had particularly bad spikes

One in 10 residents tested positive for the virus in the fall in North Dakota, and experts think many more cases went undetected

From there, the outbreak expanded beyond the Midwest, reaching both coasts and stretching down to the South in a devastating wave

The country saw more daily cases and deaths in January than any other time before or since

“You do see this movement, almost like it’s moving from county to county,” said Jeffrey Shaman, an infectious disease epidemiologist at Columbia University, who said researchers found community-to-community transmission played an important role in virus spread during the 2009 H1N1 pandemic

A sharp fall after a peak is not uncommon during epidemics, experts said

Michigan saw a large surge in cases and deaths, worrying experts that the variant would cause a similar nationwide outbreak

Epidemiologists still do not know why Michigan was unlucky — or why the outbreak did not spread to neighboring states

It’s possible that people became more cautious during the resurgence, slowing the spread, said Dr

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States lifted virtually all virus restrictions and people relaxed their behavior in celebration

Missouri saw the first big surge of the Delta wave

Vespignani said

By the end of August, most states in the South had hit new records for daily cases or deaths and the virus turned northward, causing surges in the upper Midwest and Mountain West

While the Delta wave rolled across much of the country, some places were relatively spared

Vespignani said

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 forecast a substantial winter peak in the United States this year

All the same, there are bound to remain places where the virus can spread, as each new wave has shown

“The difference between the Michigan Alpha wave in Spring 2021 and the Delta wave is really telling you that the wall that you’ve built might work for one variant, but it might not be enough for the next one,” Mr

Vespignani said