Exponential growth may explain why Omicron cases are skyrocketing in parts of the United States

A woman uses a swab to take a sample from her nostril in an NHS Test and Trace Covid-19 test unit.ADRIAN DENNIS / AFP / Getty Images

  • In pandemic terms, “exponential growth” means infections accelerate over time.

  • In New York City, the percentage of people testing positive for COVID-19 has doubled in three days.

  • The exponential growth causes huge epidemics over short periods of time. But we do know how to stop the spread of the virus.

As COVID-19 infections explode in the northeast and Dr Anthony Fauci warns Americans of a “really dark time ahead” in mid-January, a mathematical concept known as “growth exponential “is again relevant.

Understanding how exponential growth works is critical, experts say, as it explains why they are so worried about the latest wave of cases that has swept through parts of the United States. The easiest way to grasp the concept is to look at a chart, according to Zoe McLaren, an associate professor at the University of Maryland in Baltimore County, who studies policies for dealing with infectious disease outbreaks.

“It’s kind of slowly increased, and then that pace picks up – then flies away,” McLaren said of the plot of exponential growth.

Take New York City, for example, where the percentage of people testing positive for COVID-19 doubled in three days, according to Dr. Jay Varma, professor at Weill Cornell Medical School and senior health adviser to the New York mayor. Bill de Blasio, who posted the data to Twitter on Thursday.

The trajectory of these infections – almost straight up – is both informative and impossible to ignore.

Seven-day average of confirmed and probable COVID-19 cases in New York City, through December 13, 2021

Seven-day average of confirmed and probable COVID-19 cases in New York City, through December 13, 2021New York City Department of Health and Mental Hygiene

Simply put, exponential growth means the numbers – in this case, coronavirus infections – are accelerating over time. Instead of increasing by the same number of cases every day, they are doubling over a period of time.

For example: imagine doubling just one case of COVID-19 each day. After a day, there would be two cases. Two days, four cases. Three days, eight cases. Fourteen days later, there would be 16,384 cases.

This doubling phenomenon leads to an extraordinarily high number of cases much faster than most people can conceptualize, McLaren explained. And the bigger the number you start with, the bigger the explosion of infections you have every day.

“The rate increases over time, due to the doubling,” she said, adding, “When you double a very small number of cases, it always results in a small number of cases. When you double a large number of cases. case, that’s when we get these huge spikes. The spikes happened really quickly, before people knew it, because the doubling is happening over a period of days. “

This dizzying change can be hard for people to understand.

“The problem with exponential growth is that it’s not intuitive,” McLaren said. “Cases are increasing and getting out of hand a lot faster than people realize.”

While New York City officials are unsure whether Omicron’s highly infectious variant is fueling the city’s rapid increase in cases, it could potentially be a piece of the puzzle. Data from the Centers for Disease Control and Infection suggests that in the wider region, which includes New York and New Jersey, Omicron is gaining ground. It is estimated that 13.1% of samples analyzed between December 5 and 11 were an Omicron variant, up from just 2% of samples the week before.

COVID-19 has been with us for 2 years. We know how to stop the transmission.

People wearing masks line up in Austria

People waiting for a Covid-19 mass test in Vienna, Austria.Photo AP / Ronald Zak

While watching COVID-19 cases soar in a place like New York City is undoubtedly frightening because of the risk it poses to hospitals, healthcare facilities, vulnerable people, the benefit of being more than two years after a pandemic is that we know how to slow the spread of the virus.

In addition to vaccines and booster shots, lockdowns, high-quality masks and avoidance of indoor public spaces all help reduce infections, McLaren explained.

As was the case with Delta, and it will probably be true for Omicron, “people realize that there is a spike and it motivates them to change their behavior,” McLaren said, adding “people who don’t. not wanting to get COVID are always ready to take precautions, especially when transmissions climb to the top of the spike. “

In New York City, dozens of restaurants closed their doors on a preventive basis on Friday, with some announcing the closures would continue until the end of the year. Universities including Cornell University, New York University and Princeton University have canceled in-person events or announced plans for remote exams.

If people change their behavior, cases can fall as quickly as they have swollen.

“I often say that the optimal reaction to exponential growth looks like an overreaction,” McLaren said. “If you understand the trajectory, you realize you have to take some pretty big action,” she added.

“If you react to the case rates that you are seeing right now, you are going to under-react to what will be there tomorrow. You have to think about where things are going.”

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