Is herd immunity still possible? CDC messaging suggests not
Speaker 1: (00:00)
When the pandemic began leading health officials hoped herd immunity would provide a clear path back to normality. The idea goes that when a large portion of the population becomes immune to a disease, it becomes harder to spread. But what happens when a large portion of the population refuses to get immunized just recently, the CDC has moved away from messaging that touts herd immunity as a national goal for the American public signaling, a distinct shift in the fight against COVID-19 joining me now to discuss the nation's dwindling prospects for herd immunity is Rebecca fielding Miller and epidemiologist and UC San Diego professor Dr. Fielding Miller. Welcome back to the program. Hi, thanks
Speaker 2: (00:42)
For having me.
Speaker 1: (00:42)
Can you give us a quick recap on the concept of herd immunity and why it was such a strong goal in the fight against COVID-19? So I think,
Speaker 2: (00:50)
I think we've all learned a lot of new words in the last couple of years in terms of our public health jargon toolkit. So herd immunity is a really specific idea and what it means is enough people are vaccinated or not vulnerable to infection that when a virus is going around, we can sort of form a protective wall around people who aren't able to be vaccinated or who are extra susceptible. So imagine 98 people in a room and they're all vaccinated and they're all surrounding a two year old who can't get vaccinated. The virus can't break through to the vulnerable person. So as a, as a herd, as a community are protecting people. And I think that's kind of gotten confused with the idea of eradication or elimination or, or control
Speaker 1: (01:34)
When health officials began to discuss herd immunity as a way of fighting COVID. Did it always seem like a realistic prospect in the United States?
Speaker 2: (01:43)
I think that it's a hard number to calculate what percentage of people need to get vaccinated. And it depends on a lot of things. It depends on how easy it is to transmit the virus. It depends on how susceptible people are to getting the virus. And I think that in, uh, in their early days, we really confuse the idea of herd immunity. And like, just to say, enough of us are vaccinated who can get vaccinated to protect those who can't. We really confuse that with the idea of, of elimination or eradication. So COVID was never going to be eliminated through vaccination. That was never the goal, but the goal was enough. People can get vaccinated to protect people who are vulnerable. And I think with the Delta variant really taking off the, the increase in how easy it is to transmit has really made that number even harder to achieve.
Speaker 1: (02:35)
We're seeing the city see, move away from herd immunity as a tangible goal. Why is that?
Speaker 2: (02:41)
I think that has a lot to do with the Delta variant and the fact that again, herd immunity is predicated on the idea that enough people are safe, that we can protect people who are vulnerable. So babies kids under five, who can't get vaccinated in an ideal world, we could vaccinate enough people that little kids could go to T-ball or a, and not worry about it because so many people are vaccinated that the virus isn't circulating enough to get to them. The problem is the Delta variant is so infectious. That it's really that it's very easy for it to kind of slip through that wall of protective adults and kids over the age of five. And we're seeing that there's just not a willingness, um, nationwide so far among people who are eligible to get vaccinated, to protect those who can't
Speaker 1: (03:27)
Transmission is a key aspect of this. Why haven't any available vaccines been able to reliably block transmission of COVID-19
Speaker 2: (03:36)
What the vaccines are really, really good at doing is preventing kind of a systemic, like a whole body infection. So when we see these kind of breakthrough infections, what that typically is is somebody has an infection that's like living in their nose or their respiratory track. So the virus can still replicate a little bit before the vaccine can knock it out. And in that short window of time, you can still potentially breathe out enough virus to get somebody else sick, but you're sick for a shorter amount of time, which is really important because it means you have less time to breathe out that virus and you yourself are going to be healthier. And hopefully you'd be breathing on somebody who also would be sick for a shorter amount of time if they did get sick and would be breathing out that virus less well. So they do, even when there are breakthrough infections, they do severely limit how bad the spread is from a vaccinated person.
Speaker 1: (04:29)
You mentioned earlier how the Delta variant plays into this, but why is COVID-19 a particularly hard virus to achieve herd immunity for? Is it mainly due to the Delta variant or are other factors at play here?
Speaker 2: (04:43)
There are a lot of non-vaccine related reasons why it's been really hard to reach that number. For example, it's become really clear that COVID is, is an occupational disease. Um, if you look at data out of, for example, UC San Francisco that found that line cooks, um, had some of the highest rates of illness and death out of any occupation. We know that professions where you can't work from home, where you're constantly in contact with the public. Those folks are really, really high risk. And because we didn't have employment protections in place for enough people, the virus was really allowed to continue transmitting until, um, a variant came along. That was so transmissible that it made herd immunity even harder to get to, and that could continue to happen. Delta doesn't necessarily need to be the end, all be all a variance. Another one could come along that is even better at evading our vaccine. So the number of people vaccinated matters, but so does protecting people who are at the highest risk, um, socially of getting the virus,
Speaker 1: (05:41)
Given this new messaging from the CDC, what new ways can we mark progress against the virus?
Speaker 2: (05:47)
I think one thing that we can certainly keep an eye on is the, um, the case rate. Um, so here in San Diego, our case rate has been plateauing a little bit. We can see there's a really big difference between, um, the rates of illness for people who are vaccinated and not vaccinated. And I think it's really important and the county has done a really good job of using, um, some, some health equity and markers. So people who are the most vulnerable to getting sick people who, you know, live in crowded housing conditions, people who have these frontline jobs, if we see that numbers are consistently pretty low for those communities, that's a sign that we're all doing a really good job because it's, it's an airborne infectious disease and everybody's not safe. Like you're not safe until everybody is safe.
Speaker 1: (06:35)
Now, since we're moving away from herd immunity, what are the long-term strategies now of limiting the spread of COVID or even just treating COVID?
Speaker 2: (06:43)
Yeah. So the strategies really remain the same, um, that we've been talking about this whole time, um, a mask that fits you well, um, and that you're willing to wear, um, that your kid is willing to wear, um, is always going to be a really helpfulness, uh, risk mitigation strategy. I wear kn 90 fives. My daughter wears tiny child K in 95, um, spending as much time outdoors and fresh air as you can. And making sure that we have bigger social structures in place to make that easy for people, making sure that everybody who wants to get vaccinated has the opportunity. And, um, you know, the south county, um, has done a really phenomenal job in ensuring equitable vaccine access, um, making sure that people have access to paid sick leave so that if they need to stay home, they can, and they don't spread it. These are all what we call sort of like non-pharmaceutical or policy level interventions. And they're also incredibly important, just as much as these new pills that are coming out, that's really exciting or vaccines or boosters.
Speaker 1: (07:48)
I've been speaking with Dr. Rebecca fielding Miller and epidemiologist and UC San Diego professor Dr. Fielding Miller. Thank you so much for joining us.
Speaker 2: (07:57)
Speaker 3: (07:59)
When the pandemic began, leading health officials had hoped that herd immunity would provide a clear path back to normality.
The idea is that when a large portion of the population becomes immune to a disease, it becomes harder to spread.
The goal seems simple, but when a large portion of the population refuses to get immunized, or when available vaccines can't reliably halt transmission, that goal becomes increasingly murky.
Recently, the CDC has moved away from messaging that touts herd immunity as a national goal for the U.S. - signaling a distinct shift in the future of the fight against COVID-19.
Rebecca Fielding-Miller, epidemiologist and UC San Diego professor, says that Americans overestimated herd immunity at the beginning of the pandemic.
"I think in the early days, we really confused the idea of herd immunity with elimination or eradication — so COVID was never going to be eliminated through vaccination," Fielding-Miller said.
She joined Midday Edition on Wednesday with more on how public health messaging has changed in light of herd immunity's dwindling prospects.
Scientists say the pandemic will only end in the U.S. when we achieve what's called herd immunity. Play with our simulations to see how immunity can stop an outbreak in its tracks.