Coronavirus: some social distancing may need to continue until 2022, Harvard study predicts

Covid-19 outbreaks could become a seasonal affliction in short term

A South Korean woman has her temperature checked before casting her vote for the parliamentary elections in Seoul on April 15, 2020. Virus testing, social distancing and periodic lockdowns may be necessary for the next two years, a Harvard study suggested. Chung Sung-Jun / Getty ImagesShow less

A one-time lockdown will not halt the new coronavirus and repeated periods of social distancing may be required into 2022, Harvard scientists have predicted.

Their study came as the United States entered the peak of its Covid-19 caseload this week and worldwide cases approached 2,000,000 on Wednesday.

The Harvard team's computer simulation, published in the journal Science on Tuesday, assumed that Covid-19 will become seasonal, like closely related coronaviruses that cause the common cold, with higher transmission rates in colder months.

But much remains unknown, including the level of immunity in people who had the virus and recovered, and how long it lasts, the authors said.

Social distancing was so effective that virtually no population immunity is built

"We found that one-time social distancing measures are likely to be insufficient to maintain the incidence of Sars-CoV-2 within the limits of critical care capacity in the United States," said lead author Stephen Kissler from Harvard's TH Chan School of Public Health.

Sars-CoV-2 is the scientific name for the 'new coronavirus', which causes Covid-19.

"What seems to be necessary in the absence of other sorts of treatments are intermittent social distancing periods," he said.

Widespread viral testing would be required in order to determine when the thresholds to re-trigger distancing are crossed, said the authors.

The duration and intensity of lockdowns can be relaxed as treatments and vaccines become available. But in their absence, on and then off distancing would give hospitals time to increase critical care capacity to cater for the surge in cases that would occur when the measures are eased.

"By permitting periods of transmission that reach higher prevalence than otherwise would be possible, they allow an accelerated acquisition of herd immunity," said co-author Marc Lipsitch.

Egyptian clown Ahmed Naser helps children to put on face masks as a preventive measure against the spread of the coronavirus disease, in Darb Al-Ban district in Cairo, Egypt. EPA

An Egyptian municipality worker disinfects the area around the 3,200-year-old pink-granite colossal statue of King Ramses II at the entrance of the the Grand Egyptian Museum, which is currently under construction, in Giza, Cairo. AFP

Lebanese women cross an empty street in Beirut's downtown area. AFP

A doctor talks to nursing staff about sterilisation and handling suspected cases of coronavirus at a medical clinic in Benghazi, Libya. Reuters

Masked customers and employees are seen at supermarket in Amman, Jordan. EPA

Staff members put in place stickers showing distancing measures to be respected by customers, at a supermarket, in Amman, Jordan. EPA

Tailors, who are members of a civil sewing workshop, are making masks and overalls for protection from the Coronavirus, in Damascus, Syria. EPA

Members of the French Action Against Hunger NGO distribute hygiene and sanitation products to Palestinian residents of al-Ramadin village, southwest of the West Bank town of Hebron. AFP

Palestinian artists Hammam Mosallam (L) and Yussef Abu Zerr (R) apply facepaint on a mask and a child's face at their home workshop in the Nusseirat refugee camp in the central Gaza Strip. AFP

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Palestinian residents of al-Ramadin village carry packages of hygiene and sanitation products distributed by the French Action Against Hunger NGO, southwest of the West Bank town of Hebron. AFP

Iraqi soldiers stand at a checkpoint in the Adhamiya district of Baghdad. AFP

A nurse prepares bottles of sterilising fluid at the Benghazi Medical Centre in Benghazi, Libya. Reuters

Uruguayan singer Walter Javier Maulelo, stuck in Lebanon, plays guitar while wearing a mask alone on a seafront boardwalk in the northern coastal city of Batroun. AFP

A Bahraini police officer instructs a foreign worker to wear his protective mask, in the old marketplace of the capital Manama. AFP

A Bahraini police officer instructs a foreign worker on proper self-protection measures, in the old marketplace of the capital Manama. AFP

A health worker sprays disinfectant on a man in a van on the outskirts of Sanaa, Yemen. Reuters

Conversely, too much social distancing without respite can be a bad thing. Under one modeled scenario "the social distancing was so effective that virtually no population immunity is built," the paper said, hence the need for an intermittent approach.

The authors acknowledged a major drawback in their model is how little we currently know about how strong a previously infected person's immunity is and how long it lasts.

Virus likely here to stay

At present the best guesses based on closely-related coronaviruses are that it will confer some immunity, for up to about a year. There might also be some cross-protective immunity against Covid-19 if a person is infected by a common cold-causing betacoronavirus.

One thing however is almost certain: the virus is here to stay. The team said it was highly unlikely that immunity will be strong enough and last long enough that Covid-19 will die out after an initial wave, as was the case with the Sars outbreak of 2002-2003.

Antibody tests that have just entered the market and look for whether a person has been previously infected will be crucial in answering these vital questions about immunity, they argued, and a vaccine remains the ultimate weapon.

Outside experts praised the paper even as they emphasised how much remained unknown.

"This is an excellent study that uses mathematical models to explore the dynamics of Covid-19 over a period of several years, in contrast to previously published studies that have focused on the coming weeks or months," Mark Woolhouse, an infectious disease epidemiologist at the University of Edinburgh said.

"It is important to recognise that it is a model; it is consistent with current data but is nonetheless based on a series of assumptions - for example about acquired immunity - that are yet to be confirmed."