Ashish K. Jha is dean of the Brown University School of Public Health.

Two states. Two different paths in responding to covid-19. Together, they offer invaluable lessons about the road ahead for the nation — especially as infection rates creep up because of the delta variant.

The two states are Vermont and South Dakota. Both feature among the three states that Covid Act Now classifies as falling in the lowest-risk category, along with Massachusetts. This may be a surprise. While New England states are known to have done extraordinarily well in vaccinating their populations, South Dakota is in the middle of the pack. So, what explains the fact that South Dakota has infection numbers almost as low as Vermont, the most vaccinated state in the nation?

Let’s start with some basics. Vermont and South Dakota share several important similarities. Both have relatively White, older and rural populations. They have comparable median incomes. Both states have Republican governors, challenging the simplistic notion that covid risk is a partisan phenomenon.

Over the past two months, the rates of infection in Vermont and South Dakota have appeared remarkably similar. Both states have seen steep declines in cases, making both states near the best in terms of infections per population.

But this is where the similarity ends. While nearly 75 percent of Vermonters have had at least one vaccine shot, putting the state near the threshold for herd immunity, only half of South Dakotans have had at least one shot. South Dakota’s substantial population immunity instead comes in large part from prior infections, particularly during the fall. This massive surge in infections was driven by the Sturgis Motorcycle Rally in August that brought nearly half a million people to South Dakota, sparking outbreaks across that state and, indeed, the nation. With little to no interest on the part of its governor to squelch the outbreak, South Dakota reached the highest levels of infection seen by any state during the pandemic. At its peak, the state was reporting more than 160 new cases per 100,000 residents. Vermont, in comparison, never climbed above 30 cases per 100,000.

Unsurprisingly, these states experienced stunningly different outcomes. Adjusted for population, nearly six times as many people died in South Dakota from covid-19 as in Vermont (230 per 100,000 in South Dakota compared to just 40 per 100,000 in Vermont). In real numbers, while about 250 Vermont residents died from the disease, more than 2,000 South Dakotans died. And as of today, Vermont has a lower unemployment rate, suggesting that there need not be any trade-off between public health and the economy.

By some estimates, nearly half of the people of South Dakota may have been infected. These infections led to huge amounts of suffering beyond the deaths themselves. We are seeing an increasing body of evidence that many who survive serious illness from the virus have long-term complications and symptoms. When infections spike, a run on hospital beds means other people die because they can’t access hospital care, which almost surely occurred in South Dakota at the height of the surge. Vermont took a different approach, keeping public health measures in place to keep infections low and then, building up population immunity through excellent vaccination campaigns.

The virus isn’t going away. In fact, it is likely to become endemic, meaning it will continue to circulate, occasionally causing outbreaks in low-vaccination communities. Most people will encounter the virus at one point or another. And if they don’t have immunity from vaccines, many will get sick. The harms from infection are large, especially in comparison to the generally mild side-effects of the vaccines. And there is some evidence that the vaccine-induced immunity is more effective than natural infection-induced immunity. As the highly contagious delta variant spreads, states that have experienced high levels of infection such as South Dakota may be more vulnerable than highly vaccinated states such as Vermont.

In the spring of 2020, governors had to make decisions with little federal guidance and little historical precedent. But by that summer, it was much clearer how to curtail the disease, protect public health and manage the economy carefully. By following the science, Vermont saved an enormous number of lives and has now reached a degree of population immunity through vaccination that makes large outbreaks unlikely. Embracing a policy of “personal responsibility,” South Dakota did little to protect its residents, leading to the deaths of more than 2,000 South Dakotans and the suffering of tens of thousands more. To avoid more unnecessary outbreaks, we need to learn from states that have successfully weathered the pandemic, follow the science and keep vaccinating Americans.

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