The mass COVID-19 vaccination site at 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 is still under discussion. Some health officials have previously stated that it is difficult to achieve true immunity with herds, and Dr. Jeff Duchin, Public Health Health Officer – Seattle & King County, agrees.
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Herd immunity, Duchin explained, is a concept that comes from animal health. This essentially means that the population has so much immunity that a virus cannot spread effectively.
“When one person becomes infected, the surrounding people are so immune due to natural infection or vaccination that the virus cannot be transmitted in 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 pockets of unvaccinated people where measles can still spread. Until recently, it could not spread widely because so many people were vaccinated against it. In addition, according to Duchin, the measles vaccine provides long-term protection at a high level.
Since the onset of the COVID-19 pandemic, a number of people have skipped their vaccinations, which Duchin noted will be a real problem going forward. He encouraged everyone who had fallen ill – their children or themselves – to catch up on routine vaccinations, especially against measles, mumps and rubella.
As for Dudin’s herd immunity to COVID-19, it is unlikely that there will be sufficient immunity in the population to stop the spread of the virus completely.
“But I do think we can achieve a very meaningful level of population-level immunity so that our community can be protected from serious consequences, hospitalization and death, but will probably not be able to transmit the virus from person to person,” he said.
There are a few reasons why he believes this is the case, namely that there is currently no vaccine for children.
“You can not achieve herd immunity if 20% of the population is not vaccinated,” he said.
“Secondly, we need a very high level of vaccination to bring about herd immunity, and that would mean the entire population,” he added.
Initially, it was thought that herd immunity could be achieved at 70%, but due to the more transmissible variants, Duchin says, it is likely that even higher levels (perhaps 80% or more) should be vaccinated to prevent any transmission from being successful and achieve true herd immunity.
“The other complicating factor is that although vaccines are extremely effective in preventing serious diseases, and hospitalization, and even symptomatic diseases, we do not know exactly how effective they all are in preventing transmission,” Duchin said. “Initial data indicate that it will be very effective, but not 100%. This is good 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 the COVID-19 vaccines.
“It is possible that the population will have to be vaccinated again to retain immunity,” he said. “It is therefore a very important logistical challenge to have a very large part of the entire population with a high level of vaccination coverage, forever, forever.”
Finally, while the COVID-19 virus and variants are evolving, Duchin warns that it may be less susceptible to vaccine protection, and that new vaccines may need to be manufactured and adapted. Duchin compared this situation to the flu vaccines, where the virus mutates and new vaccines are developed to meet the challenge of the newly developing viruses.
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“So I think for a number of reasons that true herd immunity, which means the absolute blockade of transmission in the population, is probably not going to happen,” he said. ‘But I think what is very realistic is that we can achieve sufficient immunity through vaccination to protect our population from the most serious consequences for the health of COVID-19, hospitalization and death. And hopefully, if people are vaccinated in large enough numbers, you should reduce the number of cases dramatically. ”
“This is somewhat analogous to the flu situation where every year we have vaccines that can prevent serious illnesses, deaths, prevent hospitalizations, but prevent milder cases, transmission occurs and we have to live in equilibrium with a virus going forward,” he said. said. added. “I think high-level population immunity is probably more realistic than true herd immunity.”