After a sustained decrease in the number of COVID-19 cases in recent months, restrictions begin to ease in the United States. The number of new cases is declining or stable at low numbers in some states, but increasing in many others. Overall, the US is experiencing a sharp increase in the number of new cases per day, and by the end of June it had exceeded the maximum rate of spread in early April.
As these increasing numbers of cases are seen, it is reasonable to ask whether this is the dreaded second wave of the coronavirus, a resurgence of increasing infections after a reduction in cases.
The United States as a whole is not in a second wave because the first wave never really stopped. The virus is simply spreading to new populations or re-emerging in places that let their guard down too soon.
To have a second wave, the first wave must end
A wave of infection describes a large increase and decrease in the number of cases. There is no precise epidemiological definition of when a wave begins or ends.
But speaking of a second wave on the news, as an epidemiologist and public health researcher, I think there are two necessary factors that must be met before we can colloquially declare a second wave.
First, the virus would have to be controlled and transmission should be reduced to a very low level. That would be the end of the first wave. Then, the virus would need to reappear and cause a large increase in cases and hospitalizations.
Many countries in Europe and Asia have successfully completed the first wave. New Zealand and Iceland have also passed their first waves and are now essentially coronavirus free, with very low levels of community transmission and only a handful of cases currently active.
[[[[Get our best science, health and technology stories. Sign up for The Conversation science newsletter.]In the US, cases increased in March and April and then decreased due to the orientation and implementation of social distancing. However, the United States never reduced the spread to low numbers that held over time. Through May and early June, the numbers stagnated at approximately 25,000 new cases per day.
We have left that plateau. Since mid-June, cases have been on the rise. Furthermore, the percentage of COVID-19 tests that are giving positive results is rising sharply, indicating that the increase in new cases is not simply the result of more tests, but the result of an increase in spread.
As of this writing, new deaths per day have not started to increase, but intensive care units in some hospitals have recently reached full capacity. At the start of the outbreak, deaths often lagged behind confirmed infections. It is likely, as Anthony Fauci, the country’s leading infectious disease specialist, said June 22, that deaths will soon follow the rise in new cases.
John Nacion / STAR MAX / IPx 2020 / AP Images
Different states, different trends
Looking at the US numbers generally hides what’s really going on. Different states are in very different situations right now, and when you look at the states individually, four main categories emerge.
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Places where the first wave ends: Northeast states and some scattered elsewhere experienced large initial spikes, but were able to contain the virus and lead to new infections. New York is a good example of this.
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Places still on the first wave: Several states in the south and west, like Texas and California, had a few cases from the start, but are now experiencing massive waves with no signs of slowing down.
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Middle spots: Many states were hit early in the first wave, managed to slow down, but are on a plateau, like North Dakota, or are now experiencing sharp increases, like Oklahoma.
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Places that experience local second waves: Looking only at the state level, Hawaii, Montana and Alaska could be said to experience second waves. Each state experienced relatively small initial outbreaks and was able to reduce the single-digit spread of new confirmed daily cases, but now they are all seeing spikes again.
The trends are not surprising based on how states have been dealing with the reopening. The virus will go where there are susceptible people and until the United States stops the spread of community across the country, the first wave is not over.
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What could a second wave be like?
It is possible, although at this point it seems unlikely, that the US will be able to control the virus before a vaccine is developed. If that happens, it would be time to start thinking about a second wave. The question of how it might look depends largely on everyone’s actions.
The 1918 influenza pandemic was characterized by a slight first wave in the winter of 1917-1918 that disappeared in the summer. After the restrictions were lifted, people quickly returned to pre-pandemic life. But a second, deadliest strain returned in the fall of 1918 and a third in the spring of 1919. In total, more than 500 million people were infected worldwide and more than 50 million died in the course of three waves.
It was the combination of a quick return to normal life and a mutation in the flu genome that made it more deadly and led to the horrible second and third waves.
Fortunately, the coronavirus appears to be much more genetically stable than the influenza virus, and is therefore less likely to mutate into a more deadly variant. That leaves human behavior as the main risk factor.
Until a vaccine or effective treatment is developed, the tried and true public health measures of the past few months (social distancing, wearing universal masks, frequent hand washing, and avoiding crowded interior spaces) are ways to stop the first wave. and foiling a second one. And when there are waves like what is happening now in the US, it is necessary to suspend reopening plans.
