Home Immunity Collective immunity remains elusive due to delta variant, experts say

Collective immunity remains elusive due to delta variant, experts say



The delta variant has shifted the post of collective immunity, experts say, and although parts of Connecticut have reached this so far elusive threshold, the coronavirus may continue to circulate, becoming endemic in the state.

“The delta variant is much more contagious than the original strain of COVID,” said Scott Roberts, associate medical director for infection prevention at Yale New Haven Hospital. “Each sneeze will spread many more virus particles. Therefore, our collective immunity threshold is much higher. “

Herd immunity, Roberts explained, occurs when enough people have developed immunity to a pathogen that it cannot further spread within a community. Immunity is achieved by catching the virus or being vaccinated against it.

There have been around 350,000 confirmed cases of COVID in Connecticut according to state data, or about a tenth of the population, but Pedro Mendes, director of UConn’s Center for Cell Analysis and Modeling, said that he estimated that many, many more people in Connecticut got COVID and I never knew it.

“My models try to estimate the total number of cases (diagnosed and undiagnosed),” Mendes said. “Each of the models estimates a different number, but the estimate range is 607,000 to 812,000, or about two to three times the number of cases diagnosed.”

Add to that the 2,301,938 people who have been fully vaccinated against COVID in Connecticut so far, or 64.5% of the state’s 3.56 million people.

“Much of the initial estimates with COVID was that the herd immunity requirement was around 70%,” Roberts said. Thus, if the state had fought the original variant of the immunity of the population might have already been achieved.

“With delta, the ‘collective immunity’ threshold is much higher than what we calculated earlier this year,” Mendes said.

The key metric, according to Roberts, is called r-naught: “Basically, if an infected person comes out into the world, how many are they likely to infect?

Roberts went on to say: “A more contagious disease means we need a greater amount of herd immunity, or we need a higher proportion of the population to be immune before we achieve herd immunity. “said Roberts.

Delta, now the common strain of COVID in Connecticut, is much more contagious. This means that a much higher percentage of people need to be immunized so that the virus has nowhere to go.

“We need a higher level of population immunity to truly achieve collective immunity, where the virus will start to decline and this pandemic will end,” Roberts said. “I’ve seen studies of up to 85% for herd immunity thresholds,” he said.

It is possible, Roberts said, that parts of Connecticut where vaccination rates are particularly high, experience some population immunity.

“I think there are some areas where we could achieve that,” Roberts said.

There are other considerations to take into account, Mendes said, including how long immunity lasts after catching the virus.

“The big question is how long does the immunity to infection last,” he said. “We don’t know much about it and it could make a big difference. “

Additionally, even though parts of the state are close to popular immunity, that immunity may be waning.

“At this point, the immunity might wane,” Roberts said. “Some of the first people were vaccinated in January. Are we seeing a drop in immunity that justifies a recall? I think the short answer to this is that we are in selected populations. “

Roberts said he hopes, if the virus continues to circulate, that it mutates into a less deadly form.

“Most pandemic viruses, at some point in time, evolve to be more infectious and less fatal,” he said. “It’s kind of an evolutionary adaptation to infect as many people as possible. Essentially, if your virus is too severe, you will kill your host, you will not spread anywhere.

That would mean the virus would become ‘endemic’ and restrictive social distancing and masking requirements would no longer be necessary, even if the virus is still present.

There is a precedent. Roberts noted that the H1N1 “swine flu” was much more virulent when it was first discovered in 2009.

“We still see this virus all the time in our lab tests, but it’s certainly not at the level of severity it previously was simply because so many people are immune or the immunity from previous years continues.” , did he declare. “Although you can still get this strain of flu, it will be much less severe than it was the first time you encountered it.”

The same may happen with COVID-19 over time.

“Let’s say you had the vaccine. A year later, you are infected. You don’t have the same immunity that you had right after the vaccine, but you still have some immunity that will kick in and your illness won’t be as bad as it was, ”Roberts said. “These other people around you, you can pass it on to a lesser extent than you did the year before, and they could also be vaccinated, so it will be much less of a problem for them.”