Alaska News

Here’s what epidemiologists know so far about Alaska’s COVID-19 ‘vaccine breakthrough’ cases

We're making this important information available without a subscription as a public service. But we depend on reader support to do this work. Please consider supporting independent journalism in Alaska, at just $3.69 a week for an online subscription.

A relatively small group of Alaskans who were fully vaccinated against COVID-19 have since tested positive for the coronavirus.

They are referred to as “vaccine breakthrough” cases — and are rare compared to the total number of people fully vaccinated, health officials say. By late last week, 310 breakthrough cases had been detected in Alaska, out of the more than 250,000 Alaskans who are considered fully vaccinated.

A new report released this week by the state health department analyzed the first 152 breakthrough COVID-19 cases identified in Alaska between February and March.

The report shows that the vast majority of the breakthrough cases in Alaska have so far been mild or asymptomatic — which aligns with evidence that show the vaccines to be particularly effective at preventing severe illness and death.

The results of the report also underscore the fact that “it’s very, very uncommon to have vaccine breakthrough cases,” said Dr. Joe McLaughlin, state epidemiologist with the Alaska Department of Health and Social Services, during a call with reporters Thursday.

A small number of vaccine breakthrough cases are expected because “no vaccines are 100% effective at preventing illness,” according to a CDC webpage on vaccine breakthroughs. “There will be a small percentage of people who are fully vaccinated who still get sick, are hospitalized, or die from COVID-19,” the CDC said.

In clinical trials, the three currently available COVID-19 vaccines from Johnson & Johnson, Moderna and Pfizer were about 66%, 94% and 95% effective, respectively, at preventing symptomatic COVID-19.


[She got COVID-19, got vaccinated - and then got COVID again]

Over half of the 152 cases investigated in the Alaska report involved people who were asymptomatic for the entire course of their isolation periods. Nine percent were asymptomatic at the time of testing but later developed at least one symptom of the virus, and about a quarter were symptomatic at the time of testing.

One person with a breakthrough case in the state needed to be hospitalized, and one died, the report said. Both people had pre-existing conditions that put them at a heightened risk for severe illness for COVID-19.

“Their COVID diagnosis wasn’t a singular event that caused their hospitalization, or caused their death,” Dr. Louisa Castrodale, an epidemiologist with the state health department who helped compile the report, said Wednesday.

The majority of the cases were identified through routine, asymptomatic testing, including during travel, or before a health procedure or admit.

Alaska’s number of vaccine breakthrough cases during the time frame the report was conducted was somewhat high compared to other states, health officials said.

Partially, this was because Alaska has been conducting on average about three times as much COVID-19 testing compared to the national average — and Alaska was initially ahead of the curve with its vaccine rollout, said Dr. Anne Zink, the state’s chief medical officer, on Wednesday.

“We were testing a lot more people, and we had a lot more vaccinated,” she said. “So I think it’s important to understand how Alaska is a little different when you’re comparing these numbers to national numbers.”

The report includes a list of public health recommendations and reminders that align with recent CDC guidance for fully vaccinated people:

• Testing is no longer recommended for asymptomatic vaccinated people who are close contacts of someone with COVID-19, or who travel.

• Anyone with COVID-19 symptoms should get tested immediately regardless of their vaccination status.

• Anyone infected with COVID-19 must follow standard isolation procedures, regardless of their vaccination status.

• Those 16 and older should get vaccinated against COVID-19.

Annie Berman

Annie Berman is a reporter covering health care, education and general assignments for the Anchorage Daily News. She previously reported for Mission Local and KQED in San Francisco before joining ADN in 2020. Contact her at