It is already clear, however, that the virus is changing too quickly, new variants are spreading too easily and vaccination is proceeding too slowly for herd immunity to be within reach anytime soon.Continued immunizations, especially for people at highest risk because of age, exposure or health status, will be crucial to limiting the severity of outbreaks, if not their frequency, experts believe.
The drive for herd immunity — by the summer, some experts once thought possible — captured the imagination of large segments of the public.“People were getting confused and thinking you’re never going to get the infections down until you reach this mystical level of herd immunity, whatever that number is,” he said.Once the novel coronavirus began to spread across the globe in early 2020, it became increasingly clear that the only way out of the pandemic would be for so many people to gain immunity — whether through natural infection or vaccination — that the virus would run out of people to infect.
The concept of reaching herd immunity became the implicit goal in many countries, including the United States.Early on, the target herd immunity threshold was estimated to be about 60 to 70 percent of the population.
Fauci, expected that the United States would be able to reach it once vaccines were available.
The predominant variant now circulating in the United States, called B.1.1.7 and first identified in Britain, is about 60 percent more transmissible.As a result, experts now calculate the herd immunity threshold to be at least 80 percent.Though resistance to the vaccines is a main reason the United States is unlikely to reach herd immunity, it is not the only one.“If the coverage is 95 percent in the United States as a whole, but 70 percent in some small town, the virus doesn’t care,” he explained.In some parts of the United States, inoculation rates may not reach the threshold needed to prevent the coronavirus from spreading easily.
Any variants that arise in the world will eventually reach the United States, she noted.
Less than 2 percent of the people in India have been fully vaccinated, for example, and less than 1 percent in South Africa, according to data compiled by The New York Times.If the herd immunity threshold is not attainable, what matters most is the rate of hospitalizations and deaths after pandemic restrictions are relaxed, experts believe.Some unknown proportion of people with mild cases may go on to experience debilitating symptoms for weeks or months — a syndrome called “long Covid” — but they are unlikely to overwhelm the health care system.If communities maintain vigilant testing and tracking, it may be possible to bring the number of new cases so low that health officials can identify any new introduction of the virus and immediately stifle a potential outbreak, said Bary Pradelski, an economist at the National Center for Scientific Research in Grenoble, France.
In the long term, the public health system will also need to account for babies, and for children and adults who age into a group with higher risk“I think we’re going to be looking over our shoulders — or at least public health officials and infectious disease epidemiologists are going to be looking over their shoulders going: ‘All right, the variants out there — what are they doing
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