Herd immunity is the threshold in which enough members of a community have gained enough immunity to a virus that it can no longer spread and the chain of transmission is broken.
While communities around the world are slowly progressing toward herd immunity with the novel coronavirus, public health and infectious disease experts say the process is a long one that needs to be done slowly to protect local health systems and avoid preventable deaths from stacking up.
The process, like with other viral infections before COVID-19, would benefit significantly from the discovery of a vaccine.
“The dangers of herd immunity all at once is exactly what we were trying to avoid in the first place,” said Ingham County Health Officer Linda Vail. “Our health systems would get overwhelmed and while a lot of people would get mildly ill, some would be seriously ill and if our system is being taxed, more of those folks would end up dying who didn’t need to die.”
Earlier this week, the Washington Post reported that one of President Donald Trump’s top medical advisers, Scott Atlas, has urged the White House to embrace herd immunity as a strategy to combat the pandemic.
Atlas denied the report and said in a statement, “There is no policy of the President or this administration of achieving herd immunity. There never has been any such policy recommended to the President or to anyone else from me.”
But reports have sparked further discussion about the concept of letting the infection run wild to speed up herd immunity. That concept has been dismissed by many medical professionals, including Dr. Soumya Swaminathan, chief scientist for the World Health Organization.
Swaminathan said on a video on the WHO website reaching herd immunity naturally, without a vaccine, would “take a long time” and would “do a lot of collateral damage.”
For the community to reach herd immunity for coronavirus, infectious disease experts estimate that 60-80% of the population would need to gain immunity against the virus, either through infection of vaccination.
In Michigan, more than 100,000 confirmed cases of COVID-19 have been reported since March. That’s about 1% of the population.
“Since we do not know whether immunity is long-lasting, nor do we know the long-term effects of COVID-19, Michigan does not support allowing 80% of Michiganders being infected with this novel virus,” said Lynn Sutfin, spokesperson for the Michigan Department of Health and Human Services.
Nationwide, the U.S. has reported more than 6 million cases of COVID-19. To reach a 60% to 80% threshold, the nation would need 197 million to 262 million Americans to be infected with coronavirus.
However, further research is needed to determine the true threshold for the virus. Dr. Dennis Cunningham, McLaren Health Care medical director for infection prevention, noted that unlike viruses diseases like mumps and measles, it isn’t yet clear to what extent the novel coronavirus can mutate and if infected individuals can be re-infected later.
In the cases of mumps and measles, it took immunization coverage of 85-90% and 95%, respectively, to achieve herd immunity. Both were assisted by the discovery of a vaccine, Vail said, which allows a community to achieve immunity safely.
As of Tuesday, Sept. 1, no vaccine trials have been approved for full use in the United States. At least nine potential vaccines are in Phase 3 (large-scale efficacy tests), while 14 are in Phase 2 and 23 in Phase 1, according to a report by the New York Times. China and Russia have approved vaccines without waiting for the results of Phase 3 trials.
Earlier this month, Michigan residents were among the first in the nation to receive a trial coronavirus vaccine in the Moderna mRNA-1273 Coronavirus Efficacy vaccine study at Henry Ford Health System. About 30,000 volunteers were needed to participate in the Phase 3, randomized, double-blind trial.
As of Tuesday, the Michigan Department of Health and Human Services had reported 103,185 confirmed COVID-19 cases and 6,495 deaths associated with coronavirus since March.
“Ideally, reaching that level of immunity would accompany vaccinations and not infections in the population that can severely impact those infected,” Sutfin said. “That’s why we are urging Michiganders to minimize transmission until a vaccine is universally administered.”