The massive COVID-19 vaccination site at Seattle’s Lumen Field Events Center. (Photo courtesy of Governor Inslee / Twitter)
As more and more people are vaccinated against COVID-19, the concept of immunity in the herd continues to appear in conversations. Some health officials have previously expressed that true herd immunity can be difficult to achieve and Dr. Jeff Duchin, Public Health Officer – Seattle and King County, agrees.
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Herd immunity, Duchin explained, is a concept that comes from animal health. It basically means that the population has so much immunity that a virus cannot spread effectively.
“If a person becomes infected, the people around them are so immune due to a natural infection or vaccination that the virus cannot transmit to the population,” he said.
So far, something like herd immunity to measles has been achieved in the United States, although Duchin points out that there are pockets of unvaccinated people where measles can still spread. Until recently, it could not be widely spread because there are many people who are vaccinated against it. In addition, the measles vaccine, according to Duchin, offers long-lasting, high-level protection.
Since the onset of the COVID-19 pandemic, several people have been missing out on vaccines, which Duchin noted will be a real problem in the future. He encouraged anyone who has expired (their children or themselves) to catch up with routine vaccines, especially for measles, mumps, and rubella.
As for the herd’s immunity to COVID-19, Dr. Duchin believes it is “probably unlikely” that there will be enough immunity in the population to completely stop the spread of the virus.
“But I think we can achieve a very significant level of immunity at the population level so that our community is protected from serious outcomes, hospitalization and death, but probably not able to completely stop the transmission of the virus from person to person.” . He said.
There are some reasons why he believes this is the case, starting with the fact that there is currently no vaccine for children.
“Herd immunity cannot be achieved when 20% of the population is not vaccinated,” he said.
“Second, we would need very high levels of vaccination coverage to achieve herd immunity, and that would mean for the entire population,” he added.
Initially, it was thought that herd immunity could reach 70%, but due to the more transmissible variants, Duchin says it is likely that even higher levels (perhaps 80% or more) would need to be vaccinated to prevent any transmission is successful and the true immunity of the herd is achieved.
“The other complicated factor is that while vaccines are tremendously effective in preventing serious illness, neither hospitalization, nor symptomatic illness, we don’t know exactly how effective they will be in preventing transmission,” Duchin said. . “Initial data suggest that they will be very effective, but not 100%. Therefore, it is great news because it will reduce the risk, but it will not eliminate it ”.
Duchin also noted that the duration of protection for COVID-19 vaccines is still unknown.
“The population may need to be vaccinated again to maintain immunity,” he said. “Therefore, it is a very significant logistical challenge to continue to have a very high proportion of the entire population with a high level of vaccination coverage on an ongoing basis, forever.”
Finally, as the virus and COVID-19 variants evolve, Duchin warns that they may be less susceptible to vaccine-induced protection, perhaps requiring the production and modification of new vaccines. Duchin compared this situation to flu vaccines, where the virus mutates and new vaccines are developed to “meet the challenge of new evolving viruses.”
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“Therefore, for various reasons, I believe that the true immunity of the herd, i.e. the absolute blockade of population transmission, is unlikely to happen,” he said. “But I think what is very realistic is that we will be able to achieve a sufficient level of immunity through vaccination to protect our population from the most serious health effects of COVID-19, hospitalization and death. And , hopefully, if people get vaccinated in sufficient numbers, drastically reduce the number of cases ”.
“It is something analogous to the flu situation in which every year we have vaccines that can prevent serious morbidity, mortality, prevent hospitalizations, but there are milder cases, transmission occurs and we must live in balance with a virus in the future, ”he said. added. “I think the immunity of the high-level population is probably more realistic than the true immunity of the herd.”