Massive vaccination site COVID-19 at the Lumen Field Events Center in Seattle. (Photo courtesy of Governor Inslee / Twitter)
As more and more people are vaccinated against COVID-19, the concept of herd immunity continues to appear in the conversation. Some health officials have previously said that the true immunity of the herd can be difficult to achieve, and Dr. Jeff Duchin, a public health officer in Seattle and King County, agrees.
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The herd’s immunity, Duchin explained, is a concept that comes from animal health. In essence, it 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 strongly immune to either the natural infection or the vaccination that the virus cannot be transmitted to the population,” he said.
So far, something similar to herd immunity has been achieved for measles in the United States, although Duchin notes that there are pockets of unvaccinated people in whom measles can spread. Until recently, it could not spread widely because so many people are vaccinated against it. In addition, the measles vaccine, says Duchin, provides long-term, high-level protection.
Since the beginning of the COVID-19 pandemic, a number of people have been ignoring their vaccinations, which Duchin said will be a real problem in the future. He encouraged anyone who escaped – their children or themselves – to catch up on routine vaccinations, especially for measles, mumps and rubella.
Regarding the herd’s immunity to COVID-19, Dr. Duchin believes it is “probably unlikely” that there will be enough immunity in the population to stop the virus from spreading completely.
“But I think we can achieve a very significant level of immunity at the population level so that our community is protected from severe outcomes, hospitalization and death, but we probably won’t be able to completely stop the transmission of the virus from person to person,” he said. said.
There are several reasons why he considers this appropriate, given that there is currently no vaccine for children.
“You can’t get herd immunity when 20% of the population isn’t vaccinated,” he said.
“Secondly, we would need very high levels of immunization coverage to get the immunity of the herd and that would mean for the whole population,” he added.
Initially, it was thought that the herd’s immunity could be reached at 70%, but due to more transmissible variants, Duchin says it is likely that even higher levels – perhaps 80% or more – will be vaccinated to prevent any transmission. success and attain the true immunity of the flock.
“The other complicating factor is that while vaccines are extremely effective in preventing serious illness and hospitalization and even symptomatic illness, we don’t know exactly how effective they will all be in preventing transmission,” Duchin said. “Initial data suggest that they will be very effective, but not 100%. So this is great news, because it will reduce the risk, but it will not eliminate it. ”
Duchin also pointed out that the duration of protection is still unknown for COVID-19 vaccines.
“The population may be re-immunized to maintain immunity,” he said. So this is a very significant logistical challenge to continue to have a very large proportion of the entire population, with a high level of vaccination coverage continuously, forever.
Finally, as the virus and COVID-19 variants evolve, Duchin warns that they may become less sensitive to vaccine-induced protection, requiring new vaccines to be produced and modified. Duchin compared this situation to flu vaccines, in which the virus moves and new vaccines are developed to “respond to the challenge of new evolving viruses.”
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“So, for several reasons, I think that the true immunity of the herd, that is, the absolute blockade of transmission to the population, will probably not 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 worst health effects of COVID-19, hospitalization and death. And, hopefully, if people are vaccinated in large enough numbers, reduce the number of cases dramatically. ”
“It’s somewhat similar to the flu situation where we have vaccines every year that can prevent severe morbidity, mortality, prevent hospitalizations, but there are milder cases, transmission is happening and we have to live in balance with a virus in the future,” he said. . added. “I think the high-level immunity of the population is probably more realistic than the real immunity of the herd.”