Early in the pandemic, the term “herd immunity” was the buzzword to signal the end of the ravages of COVID-19.
Now nearly half of the country has been vaccinated, but the rates of vaccination are slipping.
There is now widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever.
Instead, they are coming to the conclusion that rather than making a long-promised exit, the virus will most likely become a manageable threat that will continue to circulate in the United States for years to come, still causing hospitalizations and deaths but in much smaller numbers.
How much smaller is uncertain and depends in part on how much of the nation, and the world, becomes vaccinated and how the coronavirus evolves. 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.
Even Dr. Fauci is acknowledging the shift in thinking about the term “herd immunity” among the experts.
“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. “That’s why we stopped using herd immunity in the classic sense,” he added. “I’m saying: Forget that for a second. You vaccinate enough people, the infections are going to go down.”
Early in the pandemic the target level for herd immunity threshold was somewhere around 60-70% of the population, to be achieved through a combination of natural immunity and vaccinations. This was based on the level of contagiousness of the original virus.
The predominant variant now circulating in the United States, called B.1.1.7 and first identified in Britain, is about 60% more transmissible, and this is causing the threshold to be revised upward to around 80%.
If even more contagious variants develop, or if scientists find that immunized people can still transmit the virus, the calculation will have to be revised upward again.
Experts believe what matters most is the rate of hospitalizations and deaths after pandemic restrictions are relaxed. By focusing on vaccinating the most vulnerable, the United States has already brought those numbers down sharply. If the vaccination levels of that group continue to rise, the expectation is that over time the coronavirus may become seasonal, like the flu, and affect mostly the young and healthy.
This story was orginally in the New York Times.
You can also read it here at the Seattle Times.