Some of that may be due to social distancing behavior, but rising rates of immunity are also a factor, according to Youyang Gu, a computer scientist whose Covid-19 Projections is among 34 pandemic models tracked by the US Centers for Disease Control and Prevention. “Immunity may play a significant part in the regions that are declining,” says Gu.
By contrast, vaccinating a sheltered older person might protect that individual but does relatively less to stop transmission. “When the disease itself causes herd immunity, it does so more efficiently than when we give out vaccine at random,” Marc Lipsitch, a public health modeler at Harvard University, told the political pundit Bill Kristol last week during a podcast interview.
This slows the pandemic down. “I believe the substantial epidemics in Arizona, Florida and Texas will leave enough immunity to assist in keeping COVID-19 controlled,” Trevor Bedford, a pandemic analyst at the University of Washington, said on Friday, in a series of tweets. “However, this level of immunity is not compatible with a full return to societal behavior as existed before the pandemic.
The nation’s leaders said last week that children would go back to school unmasked. “I would say in Sweden there is no doubt that immunity plays an important role, more than in other countries,” says Britton. “Now this epidemic is slowly stopping.
No one can say different,” says Tom Britton, a statistician who models the pandemic at the University of Stockholm. “The question is to what degree is the effect because of interventions or because of immunity?
Researchers say they hope to determine how great a role the rise of this population immunity can play in managing the pandemic. “Clearly, as susceptibility drops, disease spreading drops.
Britton says a better understanding of how population immunity is shaping outbreaks could help guide the level and intensity of social interventions.
Once an obscure inflection point known only to epidemiologists, herd immunity has gained what Francois Balloux, a systems biologist at University College London, calls “Kardashian-like” fame and become a lightning rod in politically polarized debates over economic reopening.
Others find reason to doubt that immunity will ever accumulate without a vaccine and say counting on it can only lead to millions of deaths. “It seems there is the ‘herd immunity is already reached’ team and the ‘we are all going to die’ team.
A virus outbreak will cease to grow, even without any control measures, when a threshold called herd immunity is achieved.
Whatever the reason, once these individuals become infected and are removed from the equation through death or immunity, the effect on the pandemic is outsized.
Rising covid-19 infections are making the virus harder to transmit. https://t.co/CaHfhN3Ok1— MIT Technology Review (@techreview) September 2, 2020