THE CORONAVIRUS WILL BECOME ENDEMIC a Nature Survey Shows Many Scientists Expect SARS-Cov-2 Is Here to Stay, but It Could Pose Less Danger Over Time
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Feature LISELOTTE SABROE/RITZAU SCANPIX/AFP/GETTY SABROE/RITZAU LISELOTTE Children in Copenhagen play during the SARS-CoV-2 pandemic. Endemic viruses are often first encountered in childhood. THE CORONAVIRUS WILL BECOME ENDEMIC A Nature survey shows many scientists expect SARS-CoV-2 is here to stay, but it could pose less danger over time. By Nicky Phillips or much of the past year, life in Western beginning of the year after a security guard at than 100 immunologists, infectious-disease Australia has been coronavirus-free. a hotel where visitors were quarantined tested researchers and virologists working on the coro- Friends gathered in pubs; people positive for the virus. But the experience in navirus whether it could be eradicated. Almost kissed and hugged their relatives; Western Australia has provided a glimpse into 90% of respondents think that the coronavirus children went to school without tem- a life free from the SARS-CoV-2 coronavirus. If will become endemic — meaning that it will con- perature checks or wearing masks. other regions, aided by vaccines, aimed for a tinue to circulate in pockets of the global popu- The state maintained this envia- similar zero-COVID strategy, then could the lation for years to come (see 'Endemic future'). ble position only by placing heavy world hope to rid itself of the virus? “Eradicating this virus right now from the Frestrictions on travel and imposing lockdowns It’s a beautiful dream but most scientists think world is a lot like trying to plan the construction — some regions entered a snap lockdown at the it’s improbable. In January, Nature asked more of a stepping-stone pathway to the Moon. 382 | Nature | Vol 590 | 18 February 2021 ©2021 Spri nger Nature Li mited. All rights reserved. ©2021 Spri nger Nature Li mited. All rights reserved. It’s unrealistic,” says Michael Osterholm, an ENDEMIC FUTURE epidemiologist at the University of Minnesota In a Nature poll, 89% of scientists felt that SARS-CoV-2 was either very likely or likely to become an endemic virus. in Minneapolis. How likely do you think it is that SARS-CoV-2 will become an endemic virus: But failure to eradicate the virus does not that is, one that continues to circulate in pockets of the global population? Not enough mean that death, illness or social isolation will Very likely Unlikely evidence to continue on the scales seen so far. The future 60% 5 estimate 6 will depend heavily on the type of immunity people acquire through infection or vaccination Likely Very unlikely and how the virus evolves. Influenza and the 29 1 four human coronaviruses that cause common How likely do you think it is that SARS-CoV-2 can be eliminated from some regions? colds are also endemic: but a combination of SURVEY annual vaccines and acquired immunity means NATURE that societies tolerate the seasonal deaths and Very likely Likely Unlikely Very unlikely Not enough illnesses they bring without requiring lock- 14% 25 35 17 evidence to estimate 10 SOURCE: SOURCE: downs, masks and social distancing. 119 immunologists, infectious-disease researchers and virologists from 23 countries. Percentages do not add up to 100% because of rounding. More than one-third of the respondents to Nature’s survey thought that it would be possi- That defence wanes pretty quickly so it is not many people still susceptible, scientists still ble to eliminate SARS-CoV-2 from some regions sufficient to block reinfection entirely, but it technically class it as in a pandemic phase. In while it continued to circulate in others. In seems to protect adults from getting sick, says the endemic phase, the number of infections zero-COVID regions there would be a contin- Lavine. Even in children, the first infection is becomes relatively constant across years, allow- ual risk of disease outbreaks, but they could relatively mild. ing for occasional flare-ups, says Lavine. be quenched quickly by herd immunity if most Whether immunity to SARS-CoV-2 will To reach this steady state could take a few people had been vaccinated. “I guess COVID behave in the same way is so far unclear. A years or decades, depending on how quickly will be eliminated from some countries, but large study of people who have had COVID-19 populations develop immunity, says Lavine. with a continuing (and maybe seasonal) risk suggests that their levels of neutralizing anti- Allowing the virus to spread unchecked would of reintroduction from places where vaccine bodies — which help to block reinfection — start be the fastest way to get to that point — but that coverage and public-health measures have not to decline after around six to eight months2. would result in many millions of deaths. “That been good enough,” says Christopher Dye, an But their bodies also make memory B cells, path has some huge costs,” she says. The most epidemiologist at the University of Oxford, UK. which can manufacture antibodies if a new palatable path is through vaccination. “The virus becoming endemic is likely, infection arises, and T cells that can eliminate but the pattern that it will take is hard to virus-infected cells, says Daniela Weiskopf, an Vaccines and herd immunity predict,” says Angela Rasmussen, a virologist immunologist at the La Jolla Institute for Immu- Countries that have begun distributing from Georgetown University, who is based in nology in California, who co-authored the COVID-19 vaccines soon expect to see a Seattle, Washington. This will determine the study. It’s yet to be established if this immune reduction in severe illness. But it will take societal costs of SARS-CoV-2 for 5, 10 or even longer to see how effectively vaccines can 50 years in the future. reduce transmission. Data from clinical trials suggest that vaccines that prevent Childhood virus symptomatic infection might also stop a Five years from now, when childcare centres call The virus becoming person from passing on the virus. parents to tell them that their child has a runny endemic is likely, but If vaccines do block transmission — and if they nose and a fever, the COVID-19 pandemic might remain effective against newer variants of the seem a distant memory. But there’s a chance the the pattern that it will virus — it might be possible to eliminate the virus virus that killed more than 1.5 million people in take is hard to predict.” in regions where enough people are vaccinated 2020 alone will be the culprit. so that they can protect those who are not, This is one scenario that scientists foresee contributing to herd immunity. A vaccine that for SARS-CoV-2. The virus sticks around, but memory can block viral reinfection — although is 90% effective at blocking transmission will once people develop some immunity to it cases of reinfection have been recorded, and need to reach at least 55% of the population to — either through natural infection or vacci- new viral variants might make them more achieve temporary herd immunity as long as nation — they won’t come down with severe likely, they are still considered rare. some social distancing measures — such as face symptoms. The virus would become a foe first Weiskopf and her colleagues are still tracking masks and many people working from home — encountered in early childhood, when it typi- the immune memory of people infected with remain in place to keep transmission in check, cally causes mild infection or none at all, says COVID-19 to see if it persists. If most people according to a model3 developed by Alexandra Jennie Lavine, an infectious-disease researcher develop life-long immunity to the virus, either Hogan at Imperial College London and her col- at Emory University in Atlanta, Georgia. through natural infection or vaccination, then leagues. (A vaccine would need to reach almost Scientists consider this possible because the virus is unlikely to become endemic, she 67% of people to provide herd immunity if all that’s how the four endemic coronaviruses, says. But immunity might wane after a year social distancing measures were lifted.) But if called OC43, 229E, NL63 and HKU1, behave. At or two — and already there are hints that the the rate of transmission increases because of a least three of these viruses have probably been virus can evolve to escape it. More than half the new variant, or if a vaccine is less effective than circulating in human populations for hundreds scientists who responded to Nature’s survey 90% at blocking transmission, vaccine coverage of years; two of them are responsible for roughly think waning immunity will be one of the main will need to be greater to blunt circulation. 15% of respiratory infections. Using data from drivers of the virus becoming endemic. Vaccinating even 55% of the population previous studies, Lavine and her colleagues Because the virus has spread around the will be challenging in many countries. “The developed a model that shows how most chil- world, it might seem that it could already be virus will stick around if parts of the world dren first come down with these viruses before classed as endemic. But because infections don’t get vaccinated,” says Jeffrey Shaman, the age of 6 and develop immunity to them1. continue to increase worldwide, and with so an infectious-disease researcher at Columbia Nature | Vol 590 | 18 February 2021 | 383 ©2021 Spri nger Nature Li mited. All rights reserved. ©2021 Spri nger Nature Li mited. All rights reserved. Feature University in New York City. DRIVING FACTORS for measles has never needed to be updated Even if the virus remains endemic in many Nature asked scientists to pick three of the because the virus has yet to evolve in ways that regions, global travel will probably resume biggest factors that would drive SARS-CoV-2 evade the immune system.