The massive COVID-19 vaccination site at the Lumen Field Events Center in Seattle. (Photo courtesy of Gov. Inslee / Twitter)
As more and more people are vaccinated against COVID-19, the concept of herd immunity continues to come up for discussion. Some health officials have previously indicated that true herd immunity is difficult to achieve, and Dr. Jeff Duchin, health officer at Public Health – Seattle & King County, agrees.
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Herd immunity, Duchin explained, is a concept that stems from animal health. It essentially means that the population has so much immunity that a virus cannot spread effectively.
“If a person becomes infected, the surrounding people are so highly immune, either through natural infection or vaccination, that the virus cannot be passed on to the population,” he said.
So far, something like herd immunity to measles has been achieved in the United States, although Duchin notes that there are groups of unvaccinated people where measles can still spread. Until recently, it could not spread widely because so many people have been vaccinated against it. Plus, the measles vaccine provides long-term, high-level protection, Duchin says.
Since the beginning of the COVID-19 pandemic, a number of people are skipping their vaccinations, which Duchin says will be a real problem in the future. He encouraged anyone who has expired – their children or themselves – to catch up on routine vaccinations, especially for measles, mumps, and rubella.
In terms of achieving herd immunity to COVID-19, Dr. Duchin said it is “probably unlikely” that there will be sufficient immunity in the population to completely stop the spread of the virus.
“But I do think we can achieve a very meaningful level of population-level immunity, so that our community is protected from serious consequences, hospitalization, and death, but probably won’t be able to fully transmit the virus from person to person. stop, ”he said.
There are a few reasons why he thinks this is the case, starting with the fact that there is currently no vaccine for children.
“You cannot achieve herd immunity if 20% of the population is not vaccinated,” he said.
“Second, we would need very high immunization coverage to achieve herd immunity, and that would mean the entire population,” he added.
It was initially thought that herd immunity could be achieved at 70%, but because of the more transmittable variants, Duchin says it’s likely that even higher levels – maybe 80% or more – would need to be vaccinated to prevent transmission from being successful would be and achieve true herd immunity.
“The other complicating factor is that while vaccines are immensely effective in preventing serious illness, hospitalization and even symptomatic illness, we don’t know exactly how effective all of them will be in preventing transmission,” said Duchin. “Initial data suggests they will be very effective, but not 100%. So that’s great news because that reduces the risk, but it doesn’t eliminate it. “
Duchin also pointed out that the duration of protection is still unknown for the COVID-19 vaccines.
“The population may need to be re-immunized to maintain immunity,” he said. “So that’s a very important logistical challenge to keep a very high percentage of the entire population with a high vaccination coverage forever, forever.”
Finally, as the COVID-19 virus and its variants evolve, Duchin warns that they may become less susceptible to vaccine-induced protection, potentially requiring new vaccines to be produced and modified. Duchin compared this situation to the flu vaccines, where the virus mutates and new vaccines are being developed to “meet the challenge of the newly evolving viruses.”
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“So for a number of reasons, I think that true herd immunity, that is, the absolute block of transmission in the population, is unlikely to happen,” he said. “But I think it is very realistic that through vaccination we can achieve sufficient immunity to protect our population from the most serious health effects of COVID-19, hospitalization and death. And, hopefully, if people get vaccinated in large enough numbers, you will drastically reduce the number of cases. “
“It is somewhat analogous to the flu situation where we have vaccines every year that can prevent serious morbidity and mortality and prevent hospitalization, but milder cases do occur, transmission is occurring and we have to live in equilibrium with a virus in the future,” he added. “I think high-level immunity is probably more realistic than true herd immunity.”