Alaska’s ‘breakthrough’ COVID cases on par with expectations, state epidemiologist says

A person wearing blue gloves draws liquid from a vial into a syringe
A nurse draws a dose of the Johnson and Johnson vaccine from a vial at a city vaccine clinic at Tikahtnu Commons in Anchorage in Aug. 2021 (Lex Treinen/Alaska Public Media)

Since Feb. 1, 8.6 percent of COVID-19 cases in the state have been in vaccinated Alaskans.

Health officials point out that means vaccines offer quite a bit of protection — especially since studies have shown that vaccinated individuals are much less likely to have serious symptoms or die from the disease.

As State Epidemiologist Dr. Joe McLaughlin told Alaska Public Media’s Casey Grove, there are some nuances in the numbers related to breakthrough infections, but the proportion in Alaska is about what you would expect.


This interview was lightly edited for clarity.

Dr. Joe McLaughlin: The mRNA vaccines are probably about 88% effective based on at least two or three studies that have come out recently. So, you expected to see vaccine breakthrough cases — if you have 100 people who all got an mRNA vaccine, and you expose all 100 of them to the SARS-CoV-2 virus, you would expect about 12 are actually going to come down with COVID-19 illness.

Now, it’s important to also point out that if you have another 100 people and none of them have been vaccinated and none of them had prior COVID infection, and you expose all 100 of those people to the virus, all 100 are likely to get infected.

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Casey Grove: What’s actually going on inside the body of somebody with a breakthrough case? Did they just not react to the vaccine in a way to produce the antibodies that they would need? Or is it more complicated than that?

Alaska state epidemiologist Dr. Joe McLaughlin. (DHSS)

JM: It’s a good question. It’s likely exactly what you said. There was a study that came out in the last couple of weeks showing that among health care workers in one facility — they looked at all of the health care workers who had been vaccinated — and, periodically, they checked their antibody levels against the SARS-CoV-2 virus.

What they found is that those people who ultimately developed a vaccine breakthrough case tended to have lower antibody levels than people who did not have a vaccine breakthrough case.

So that indicates what’s probably what’s happening for most of the vaccine breakthrough cases is that those folks probably have a lower antibody titer than the non-breakthrough cases, in general.

There are other factors that could be at play as well. For example, if you’re a health care worker, and you’re caring for somebody who’s really sick with COVID, and you’re in that medical room, and maybe you don’t have the perfect personal protection precautions and you’re exposed to a lot of the virus — if you get a real high inoculum of the virus that you’re taking in — it might be harder for your immune system to fight off all those virus particles that you’ve being exposed to. So that can also probably play into vaccine breakthrough cases.

CG: That’s interesting. And then I just wanted to address really quickly. On Talk of Alaska, we had someone from the Yukon-Kuskokwim Health Corporation, who mentioned that like 24% of the cases that they were seeing where breakthrough cases. That seems considerably higher than the 8% or so that you mentioned?

JM: So let me try and explain what’s happening there. There are many factors that affect the proportion of reported cases that are vaccine breakthroughs. Here’s some of the main ones.

The first is: The mRNA vaccines, as we talked about, are not perfect. So that plays into it.

Then the next thing is: So long as the virus continues to circulate in communities, the number of vaccine breakthrough cases is going to increase as the proportion of the population that’s vaccinated increases. It’s just simple math: if you’ve got a larger denominator — a larger pool of people who are fully vaccinated — and that virus is still circulating, it’s just a numbers game.

So the more people who are fully vaccinated, you’ve got circulating virus, the more people that you’re going to see get a breakthrough infection.

And then the last one is: Not everyone is equally likely to get tested, and not all cases of COVID are detected in a population.

So, for example, people who are less likely to get vaccinated might also be less likely to go in and get tested. We don’t know that for sure. But that’s possible.

And if that’s the case, then a smaller proportion of the detected cases — the true cases that are occurring in that population — a smaller proportion of those detected cases would be among unvaccinated people. Because let’s just say maybe unvaccinated people might be less likely to go in and actually get tested if they have mild or moderate symptoms.

So, that could also play into why the numbers are a little bit higher in the fully vaccinated group.

RELATED: COVID-19 patients at Alaska’s hospitals are mostly younger, sicker and unvaccinated

CG: My understanding is that part of the risk of having a large unvaccinated population is that that allows the virus to mutate more because it’s just in more different people and there’s just more cases. Is that right? Are we potentially looking at other variants out there somewhere in the future?

JM: Yes. Basically this virus has a spell checker that is not perfect. So every now and again, when the virus replicates in the human body, it makes errors in replicating its genomic sequence. And usually when it makes those errors, that is to the detriment of the virus. The virus does not fare as well as if it hadn’t made those errors in sort of its replication process.

But occasionally, the error that it makes winds up being beneficial for the virus. For example, it might make the virus have an ability to bind to human cells more tightly or it might allow the virus to enter the cell more efficiently. And when that happens, it creates a strain that is more easily transmissible to other people. Some of the mutations that occur can also allow the virus to evade prior immunity.

The delta is a great example. You’ve got a virus now that’s much, much more transmissible than the original strain. So it is now by far and away the predominant strain circulating in Alaska.

Casey Grove is host of Alaska News Nightly, a general assignment reporter and an editor at Alaska Public Media. Reach him at Read more about Casey here

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