As delta variant spreads, Colorado sees rise in breakthrough COVID infections

Priscilla Martinez had just finished eating a tuna sandwich at her desk at JBS USA’s corporate office in Greeley one day last week when a stark realization hit her: She had neither tasted nor smelled the typically pungent dish during the entire meal.

The 35-year-old is fully vaccinated against the coronavirus, having received her second dose in March during an employee vaccination drive held by the company, which has been hit hard by COVID-19 outbreaks.

But now, five months after getting vaccinated, Martinez began developing mild symptoms of the virus — and on Sunday, she tested positive.

“I know I wasn’t immune to it so I wasn’t surprised when I got it,” said Martinez, who feared getting a severe case of COVID-19 because she has asthma. She added, “I feel like if I didn’t have the vaccine I would be really sick right now.”

As the virus’s delta variant became the predominant strain in Colorado this summer, the number of new infections among vaccinated people in the state has increased — raising concerns this version of the virus is breaking through the vaccines’ protection more often than previous strains.

“It does look like there is a little bit more breakthrough infection occurring with the delta variant,” said Dr. Rachel Herlihy, the state epidemiologist, adding, however, that public health officials “know a little bit less about (severe) breakthrough cases.”

She stressed that while breakthrough cases are up, COVID-19 vaccines still offer high protection against severe disease that can cause hospitalization or death. The majority of infections, hospitalizations and fatalities are among people who are not vaccinated.

Breakthrough infections slowly began to rise in Colorado in late June as overall cases increased and by August had reached their highest point since the vaccines first became available in December.

The state recorded an average of 1.14 breakthrough infections per 100,000 residents on June 9 and saw a nearly eightfold increase in three months, with an average of 9 breakthrough cases per 100,000 people on Aug. 9, according to the latest data from the Colorado Department of Public Health and Environment.

Still, breakthrough cases remain low compared to infections among those who have not received any shot or are only partially vaccinated. By comparison, there were on average 28.8 cases per 100,000 people among the unvaccinated on Aug. 9.

The state’s data shows that people who are unvaccinated or only partially vaccinated are at least three times more likely to have a confirmed case of COVID-19 than people who are fully immunized.

Still much to learn about delta

There is much still unknown about breakthrough cases, including how delta spreads among the vaccinated. And state public health officials have said for months that such infections would become more common as more of the state’s population becomes inoculated.

Some increase in the percentage of infections happening in vaccinated people is just a function of math. In a population where no one has gotten a shot, there are no breakthrough infections. If every person were inoculated, any infections would be breakthroughs — though the odds of getting sick would be significantly lower than in the population where no one was protected, said Talia Quandelacy, an assistant professor at the Colorado School of Public Health.

She said COVID-19 vaccines still dramatically reduce the odds of getting seriously sick, so people need to understand that getting the shot is still valuable — even if they get a breakthrough infection.

“That’s the best way to prevent hospitalization or even a death,” Quandelacy said.

It’s not the first time that data has suggested an increase in breakthrough infections because of the delta variant. In Mesa County, which is where the variant first appeared in Colorado, state and federal public health officials found the county registered more than expected infections among vaccinated residents.

A recent analysis by The New York Times also found breakthrough infections accounted for at least one in five new COVID-19 cases in six states, including Colorado, following the arrival of the delta variant. It also found a higher percentage of hospitalizations and deaths than previously expected.

There is some data suggesting older people and those with compromised immune systems may still be at a higher risk for severe illness even after vaccination, especially as the variant continues to circulate, Quandelacy said. Still, the risk is lower than if those same people had remained unvaccinated, she said.

It’s especially important for people to get immunized because not only is the delta variant more transmissible than previous versions of the virus, but it also appears to cause more severe disease, Herlihy said.

Understanding how prevalent COVID-19 infections are among vaccinated people is important because it might change how they consider their risk in partaking in everyday activities.

The possibility that people immunized may still spread the virus and that there may be waning immunity has also been the impetus behind changing federal guidelines for mask-wearing — the Centers for Disease Control and Prevention now recommends it regardless of vaccination status — and plans to administer booster shots.

However, the CDC recently has drawn criticism for its use of “outdated and unreliable data” on breakthrough cases after deciding in May to only track such illnesses if they were severe enough for hospitalization or death, Politico reported Wednesday.

Mild symptoms, lower risk of hospitalization

A majority of the approximately 50 people who experienced breakthrough infections and responded to a query from The Denver Post reported they only experienced mild symptoms of COVID-19, such as loss of taste and smell, cough, nausea, and fatigue

“It felt like a bad cold,” said Katie Song, a Denver resident who had a breakthrough case in July while pregnant. “I’m incredibly thankful to my past self for choosing to get (the shot).”

The CDC released a study Tuesday of COVID-19 cases in Los Angeles County that found hospitalizations were 29 times more likely to occur in unvaccinated people than those who were immunized.

The number of vaccinated people hospitalized with COVID-19 in Colorado more than doubled between June and August.

The state recorded an average of 3.9 hospitalizations per 100,000 people among immunized residents on June 9. That average increased to 9.9 hospitalizations per 100,000 residents on Aug. 9, according to state data.

By comparison, the were on average 54.4 hospitalizations per 100,000 people among the unvaccinated as of Aug. 9.

Officials with the state health department cautioned that the number of vaccinated people hospitalized directly due to COVID-19 — not just people who are infected but hospitalized for other reasons — is likely lower, but did not provide that data.

Aurora resident Daniel Richard, who is fully vaccinated, developed a more serious case of COVID-19 in June after attending an improv class with 10 other people. Everyone in the class had to show proof of vaccination to attend, yet six people — including Richard — ended up contracting the virus.

“I had no idea I had a high chance of getting sick,” the 37-year-old said. “It’s affected my life for years to come.”

Richard developed blood clots in his legs and lungs after his COVID-19 infection.

He already had a pre-existing blood clot disorder, but his was case was severe enough that he ended up in the intensive care unit at UCHealth’s University of Colorado Hospital and is now being treated for “long COVID,” meaning his symptoms have persisted for longer than a couple of weeks.

Still, Richard does not regret getting vaccinated, saying he believes the decision to do so saved his life.

“When do I get the booster?” he asked.

Denver Post reporter Meg Wingerter contributed to this report.