As Gov. Gavin Newsom and other officials plan to ease strict stay-at-home orders, a major new study delivers sobering news: Unless hospitals boost capacity, or a treatment or vaccine is developed, a strategy of prolonged or intermittent “social distancing” may be needed for the next two years.
The research, published Tuesday in the journal Science, shows that there’s no way through this pandemic without more hard times. While one-time social distancing may suppress the number of critically ill patients, it concludes, infections will resurge once these measures are lifted, overwhelming hospitals.
Researchers at Harvard’s prestigious Harvard T.H. Chan School of Public Health conceded that repeated restrictions would have profound economic, social and educational consequences.
But this strategy – lifting and re-imposing restrictions such as school, business and event closures — will create smaller outbreaks of illness that can be better managed by hospitals, saving lives, they said.
Over time, this approach will lead to the build up of so-called ‘herd immunity,’ when so many people are immune that an infected individual has little chance of coming into contact with someone who is vulnerable, they said.
“Several rounds of social distancing will be required to get us to ‘herd immunity,’ in the absence of vaccination,” said Harvard epidemiologist and study co-author Dr. Marc Lipsitch at a Tuesday press conference.
The goal of on-and-off restrictions, added co-author Stephen M. Kissler, is to flatten the curve of new cases and approach ‘herd immunity’ as slowly as possible.
The team, comprised of some of the nation’s top disease-modeling experts, warned of an intense outbreak of COVID-19 next winter — when social distancing is relaxed and virus transmissibility is heightened, overlapping with flu season and stressing hospital capacity.
They built multi-year models using data on seasonality from known human coronaviruses and assuming some protection, called “cross-immunity” between the COVID-19 virus and other coronaviruses.
A prediction by the White House Coronavirus Task Force that the nation’s outbreak will end in July or August “is not consistent with what we know about the spread of infections,” because many people are still susceptible, said Lipsitch.
In his Tuesday press briefing, Gov. Newsom hinted that Californians may face future restrictions. His team is developing guidelines for when to ask Californians to stay home again if necessary, he said.
The Harvard team’s mathematical models of various disease trajectories point to the urgent need for innovation to bring the pandemic under long-term control.
“New therapies and vaccines… all of those can change what happens,” said Kissler, an expert in the use of mathematical models to study the spread of infectious disease.
For now, the best strategy allows flexibility in the timing and duration of “social distancing” restrictions, according to the Harvard team.
When restrictions are in place, the level of illness will fall — so that when they’re lifted, “the number of cases is small enough to avoid overwhelming our intensive care capacity,” said Lipsitch.
While strict measures quickly reduce the number of illnesses and deaths, loose measures will move us faster towards ‘herd immunity.’
“It’s all a trade off, in terms of cases now vs. cases later,” he said.
Ideally, we’ll inch towards the optimal level of societal immunity, without overshooting it and causing unnecessary illness and death, said Kissler.
Based on early estimates of this virus’s infectiousness, we will likely need at least 70% of the population to be immune to have herd protection, according to Johns Hopkins School of Public Health epidemiologists Gypsyamber D’Souza and David Dowdy.
Some studies suggest the herd immunity to this virus is larger and building faster than daily case counts would indicate, because people with mild symptoms aren’t tested. But another new study points the opposite direction: People with mild illness didn’t have many antibodies, it found, so they’re unlikely to be protected.
It is also essential to conduct long-term serology studies, which measure antibodies in the blood of infected individuals, so we know how many people are protected, the team added.
For now, “unless there is some enormously larger ‘herd immunity’ than we are aware of, the large majority of the  population in this country and in most parts of the world remains susceptible,” said Lipsitch.
Their models did not look at the many ways that different strategies — such as open schools but closed businesses, or small event but not large events — would affect outcomes.
And there’s one key factor that is unknown: the rate at which viral immunity might wane, over time.
One of their models shows a resurgence in the COVID-19 virus could occur as far in the future as 2025, if a vaccine is not developed.
The models also made these points:
  • an outbreak can occur at any time of year, regardless of season. But if COVID-19 follows the seasonal pattern of influenza, winter/spring outbreaks could be less severe, while autumn/winter outbreaks could be more severe.
  • If immunity is permanent, the virus could disappear for five or more years after causing a major outbreak.
  • If immunity isn’t permanent, the virus will likely enter into regular long-term circulation, like influenza.
  • Even if immunity just last for two years, “cross immunity” from related viruses could eliminate the transmission for up to three years before a resurgence in 2024, if it doesn’t fully die out.
  • There could be geographic differences in seasonal variation, like flu. And regions with a smaller number of cases during the initial wave could have larger recurrent waves later.
The team stopped short of making a formal recommendation to elected leaders and local health officials.
“Our goal in modeling such policies is not to endorse them but to identify likely trajectories of the epidemic under alternative approaches,” they wrote.
“We do not take a position on the advisability of these scenarios given the economic burden that sustained distancing may impose,” they wrote, “but we note the potentially catastrophic burden on the healthcare system that is predicted if distancing is poorly effective and/or not sustained for long enough.”