Breakthrough COVID Cases Among Those Fully Vaccinated Are Rising In Colorado

Kevin J. Beaty/Denverite
Medical assistant Yasmin Tellez preps a Moderna COVID-19 vaccination at Globeville’s Clinica Tepeyac. Jan. 26, 2021.

The percentage of COVID-19 infections among fully vaccinated Coloradans grew sharply in July, prompting Gov. Jared Polis to ask federal authorities to speed authorization of a booster shot for older adults.

While still making up just three percent of all COVID-19 infections in the state since Jan. 1, the so-called “breakthrough cases,” or infections among people previously fully vaccinated, were 20 percent of all identified cases in the first three weeks of July in the state.

Those three weeks accounted for more than 35 percent of the breakthrough cases recorded in the state since the start of the year. 

“There's increasing evidence that despite being vaccinated, you can still spread the virus, even though you yourself might not have symptoms, and so you might spread it to others who are unvaccinated, who could then have very severe symptoms,” Polis said, urging Coloradans to get vaccinated. “I know we're all very tired of this virus. We're really in the final phases. Most importantly, we have a highly effective tool to combat it.”

State epidemiologist Dr. Rachel Herlihy said Colorado documented 2,074 cases, 92 hospitalizations and three deaths among fully vaccinated residents from July 1 to July 24. The unvaccinated accounted for 80 percent of cases, 87 percent of hospitalizations and 92 percent of deaths. 

So in other words, breakthrough cases for just those three weeks represented about 20 percent of cases, 13 percent of hospitalizations and 8 percent of deaths. For the period Jan. 1 through July 24, breakthrough cases in the state represented a smaller share of the pandemic burden: just three percent of cases, four percent of hospitalizations and three percent of deaths. 

Breakthrough cases and the Delta variant

Hart Van Denburg/CPR News
Christy Harmon, left, and Barbara Maurath prepare vaccine doses at Shorter Community African Methodist Episcopal Church in Denver, on Sunday, Feb. 7, 2021.

The 5,818 recorded breakthrough cases since Jan. 1 mean fewer than one quarter of one percent of the more than three million fully vaccinated Coloradans later tested positive for COVID-19. But the 20 percent breakthrough figure also comes as an unexplained surprise and far exceeds anything seen throughout the pandemic, in Colorado or other states reporting their breakthrough case numbers. A recent report from the Kaiser Family Foundation found the reported share of COVID-19 cases among those not fully vaccinated ranged from 94.1 percent in Arizona to 99.85 percent in Connecticut. That analysis had data from only 24 states and not Colorado, but Colorado’s three percent rate of breakthrough cases since Jan. 1 remains in line with other states.

Herlihy said in the last few weeks “the proportion of cases occurring among vaccinated people has grown a little bit more than we've expected and is now closer to that 80% vaccine effectiveness range.” She said that increase could be linked to the Delta strain, but cautioned that this analysis is a “crude estimation," not from a controlled study, so it needed to be interpreted carefully.

“There's a lot more we need to understand about the Delta variant in our immune response to infection and vaccination over time. I also want to be perfectly clear that 80% effectiveness for a vaccine is still a highly effective vaccine,” she said.

But while Herlihy expressed a cautious search for answers, Polis said he is urging the federal Food and Drug Administration to “quickly review Pfizer's request to allow for a third dose by cutting red tape. And I'm aware that some Coloradans have already taken matters into their own hands. They're getting that third dose and it's really important that the FDA moves at the speed of the pandemic and meet people where they are at. And I really hope that the FDA can rise to the occasion to help end this pandemic.”

The FDA has yet to authorize booster shots of the vaccine. Nor has the agency yet granted full authorization to any of the three COVID-19 vaccines now in routine use under “emergency use authorization” procedures by the FDA. Polis also called for that process to be expedited.

Herlihy said 95.5 percent of the virus being sequenced in Colorado now is the highly transmissible delta strain. 

“Clearly that is what is driving our pandemic right now,” she said.

She also showed graphs looking at breakthrough cases by age group and vaccine type.

“We see fewer than expected vaccine breakthrough cases in children, 12 to 17, but more in older age groups,” she said. “We are seeing more vaccine breakthrough cases with the Janssen, or Johnson and Johnson vaccine, and the Pfizer vaccine compared to Moderna.” 

She said the state is investigating that trend.

Hospitalizations and the Delta variant

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An ICU nurse at Rose Medical Center, Denver, Nov. 13, 2020.

Polis also announced the state had reached a new threshold of 70 percent of all eligible Coloradans having gotten vaccinated. After having reached that level for all eligible adults in early July, he said that a new level of 72.12 percent has been reached because “we've now made enough progress with 12 to 17 year olds where we have achieved the 70 percent vaccination rate for the entire eligible population.”

But he said the delta variant is roaming unabated through the unvaccinated population and that’s driving hospitalizations, now at 358 and up from the prior week.

Herlihy said Colorado had seen about  30 percent week over week increase in cases. “So we certainly are seeing a pretty rapid increase in cases in the state at this point,” she said. “We really see that unvaccinated individuals are really driving transmission in the state right now. Overall, we see about five to six times the rate of infection in unvaccinated individuals compared to fully vaccinated individuals.”

With a mix of positive and negative indicators and plenty of uncertainty ahead of the start of school, Polis struck a middle ground tone. “It's not a time for alarm, but it's also not a time for putting our heads in the sand. We need to use the science to really guide a response that meets the needs of where we are,” he said.  

“The good news is our hospital capacity is not in jeopardy and we don't expect it to be in jeopardy, thanks to the 70 plus percent of Coloradans who have gotten vaccinated,” he said.  

Polis said if the state can't achieve 80% vaccination rates, the outlook will get worse, and the state could see hospitalizations in the range of 700 to 900 patients with COVID-19 needing hospital care.  That’s roughly double where Colorado is now, and would be the highest the state has seen in months, but lower than the peak of nearly 2,000 late last year.

“Our North Star from the very start has been to avoid overwhelming the ability of our hospitals and doctors and medical system to provide the very best quality of care to Coloradans in need,” he said.

Polis and Herlihy both urged continued vaccination as the most sure path out of the pandemic. 

“Overall, we continue to have highly effective vaccines and vaccines really continue to be the best strategy to control the pandemic in the state,” Herlihy said.

Vaccine and mask mandates

Hart Van Denburg/CPR News
Masks litter alleys and sidewalks in Denver’s LoDo and RiNo neighborhoods during the coronavirus pandemic, Thursday, March 11, 2021.

Denver took an aggressive step toward increasing vaccination Monday by ordering all city and school employees, along with health care and nursing home workers, to be vaccinated by Sept. 30.

“No one wants to relive the horrors of last year,” said Denver Mayor Michael Hancock. “No one wants to see another stay-at-home order to stop a crisis that threatens to overwhelm our hospitals.”

Given the state of pandemic, with millions of Coloradans still unvaccinated, and  those younger than 12 still ineligible, reporters asked why the state has to date resisted a return to a statewide mask mandate, like Polis ordered last year.  

On Monday, Louisiana Gov. John Bel Edwards reinstated a statewide indoor mask mandate for everyone ages 5 and above. That state is seeing much higher levels of COVID19 transmission, hospitalization and death than Colorado.

“Well, a statewide mask requirement would be an extraordinary step,” he said. It was one that we didn't hesitate to take when our hospital capacity was in jeopardy and that we sought to remove the minute we reached the conclusion that our hospital capacity was no longer in jeopardy. It's not the type of step that is normally appropriate in non-emergency circumstances.”

He said masks “are not nearly as effective as vaccinations,” and there are scenarios where there's a trade-off between masks and vaccinations. 

He further talked through his thinking. 

“We don't want people, for instance, thinking ‘I don't need to get vaccinated because I wear a mask.” He said many employers say “‘if you are vaccinated, you don't need a mask.’ And so that can be another reason to get vaccinated. And we don't want a mask wearing to be an excuse, not to get vaccinated.”

Denverite Staff Writer David Sachs contributed to this report.

Editor's note: This story has been updated to reflect the percentage of fully vaccinated individuals with a recorded breakthrough case.