[Donger]

The Best Case

I’ve been speaking to epidemiologists about their best- and worst-case scenarios to gauge what may lie ahead and see how we can tilt the balance. Let me start with the best case, since we could all use a dose of hope — which may even be therapeutic — before presenting a bleaker prognosis.

“The best case is that the virus mutates and actually dies out,” said Dr. Larry Brilliant, an epidemiologist who as a young doctor was part of the fight to eradicate smallpox. Brilliant was a consultant for the movie “Contagion,” in which a virus evolved to become more deadly, but that’s the exception. “Only in movies do viruses seem to become worse,” he explained.

Two other lethal coronaviruses, SARS and MERS, both petered out, and that is possible here. “My hope is that Covid-19 will not survive,” said Dr. Charles G. Prober, a professor at Stanford Medical School.

Several countries have shown that decisive action can turn the tide on Covid-19, at least for a time. China, astonishingly, on Thursday reported not a single new case of domestic transmission. While China is still vulnerable to a second wave, it has apparently shown that the virus can be squelched.

The West isn’t going to copy the coercive tactics of China, but Singapore, Taiwan, South Korea and Hong Kong have also demonstrated that, at least temporarily, the virus can be controlled.

Singapore and the other successful Asian models responded with the standard epidemiological tool kit: vigilance and rapid response, testing, isolating the sick, tracing contacts, quarantining those exposed, ensuring social distancing and providing reliable information. They did not shut down their entire countries, and Singapore managed to keep its schools open throughout.

“Singapore is a best-case scenario,” said Dr. Tom Frieden, a former director of the Centers for Disease Control and Prevention. He said that there was some possibility that with social distancing and limits on gatherings, the United States could knock down the numbers of infections and begin to adopt Singapore-style strategies to reduce new infections.

“The most important lesson is that the virus can be contained if people are responsible and adhere to certain simple principles,” said Dr. Christopher Willis, a physician in Singapore. “Stay calm. For most people it’s like the common cold.”

Dr. Tom Inglesby, an expert on pandemics at the Johns Hopkins Bloomberg School of Public Health, said, “The fact that Singapore, Hong Kong, Taiwan, South Korea and China — and to some extent Japan — have all flattened their curves despite having the initial onslaught of cases should give us some hope that we can sort out what they’re doing well and emulate it.”

One encouraging sign is that in Washington State, which had an early outbreak, the number of positive tests appears stable.

The weather may also help us. Some respiratory viruses decline in summer from a combination of higher temperatures and people not being huddled together, so it is possible that Northern Hemisphere nations will enjoy a summer break before a second wave in the fall. That’s what happened during the 1918 Spanish flu pandemic: It hit in the spring of 1918, went away but returned worse than ever in the fall.

Of the four coronaviruses that cause the common cold, two diminish in warm weather, while two are more variable. SARS and MERS did not have clear seasonal variations, and even seasonal flu is transmitted in the summer, although less than in winter. So while experts hope that hot weather will shortly bring a reprieve from the coronavirus — the flu is already on the retreat — there’s no solid evidence.

One reason for measured optimism is the prospect that antiviral medicines will beat the coronavirus; some are already in clinical trials. Scientists have hopes for remdesivir, originally developed for Ebola; chloroquine, an old anti-malaria drug; and some anti-H.I.V. and immune-boosting drugs. Many other drugs are also lined up for trials.

Even without proven treatment, the coronavirus may be less lethal than was originally feared, so long as health care systems are not overwhelmed. In South Korea and in China outside Hubei Province, about 0.8 percent of those known to be infected died, and the rate was 0.6 percent on a cruise ship.

That’s still roughly six times the rate of seasonal flu, about 0.1 percent, but Dr. John Ioannidis of Stanford University argues that the fatality rate may end up even lower. He warns that we are engaging in hugely disruptive interventions without firm evidence of the threat that the virus poses. Singapore has had more than 200 confirmed cases of the virus and not a single death.

About four out of five people known to have had the virus had only mild symptoms, and even among those older than 90 in Italy, 78 percent survived. Two-thirds of those who died in Italy had pre-existing medical conditions and were also elderly; Dr. David L. Katz, the former director of the Prevention Research Center at Yale University, notes that many might have died soon of other causes even if the coronavirus had not struck.

That said, a new C.D.C. study finds that of coronavirus cases in the United States requiring admission to the intensive care unit, nearly half involved patients under age 65; there is also concern about lasting lung damage among survivors.

Putting it all together, Dr. Tara C. Smith, an epidemiologist at Kent State University, said: “I’m not pessimistic. I think this can work.” She thinks it will take eight weeks of social distancing to have a chance to slow the virus, and success will depend on people changing behaviors and on hospitals not being overrun. “If warm weather helps, if we can get these drugs, if we can get companies to produce more ventilators, we have a window to tamp this down,” Smith said.