Nearly 18% of new COVID-19 infections in Arizona last month were ‘breakthrough’ cases – The Arizona Republic

Breakthrough COVID-19 infections in Arizona rose to nearly 18% of new cases in September, but state health officials emphasize vaccination remains the best way to prevent serious illness and death.

Ever since the highly contagious delta variant of the SARS-CoV-2 virus, or new coronavirus, took hold in the U.S. and Arizona in early summer, rates of breakthrough COVID-19 infections have been climbing.

As of September, breakthrough infections comprised 17.87% or about one in six new COVID-19 cases, according to data from the Arizona Department of Health Services.

In July, the breakthrough rate was 14% of new cases and in August it went up to 15%, state data shows.

Overall, state health officials say they have recorded 35,697 breakthrough COVID-19 infections in Arizona. The count of breakthrough infections specifically for September was not immediately available on Friday, only the percentage.

In Arizona, the majority of positive COVID-19 cases — about 82% — are happening in people who are unvaccinated, state health officials say.

Also, hospital leaders report that a vast majority of people hospitalized with COVID-19 illness in Arizona are unvaccinated.

“No vaccine is 100% effective, but all available COVID-19 vaccines have proven to be highly effective at reducing severe illness, hospitalization and even death,” Tom Herrmann, Arizona Department of Health Services spokesperson, wrote in an email.

“We strongly urge you to roll up your sleeve and get vaccinated today at one of the hundreds of providers around Arizona. The vaccine is our best line of defense against COVID-19. It protects you, those you love, and your community.”

Breakthrough deaths in Arizona: 238

Several high profile people, including members of Congress, have gone public with breakthrough diagnoses in recent weeks, drawing more attention to the fact that one can become infected with the SARS-CoV-2 virus that causes COVID-19 even when vaccinated.

The Broadway musical “Aladdin” recently announced it would temporarily suspend performances because of breakthrough infections among some company members, according to various media reports.

Last week Variety reported that Emmy winner Marc Pilcher, a hair and makeup designer for the Netflix series “Bridgerton,” had died of breakthrough COVID-19 at the age of 53.

The definition of a breakthrough COVID-19 infection is a positive case in people who were diagnosed at least 14 days after they were fully vaccinated. About 3.8 million Arizonans are fully vaccinated.

Breakthrough deaths are rare, but they are happening in Arizona.

State health officials said that as of Oct. 4,  preliminary data shows there had been 238 known breakthrough COVID-19 deaths in the state, which is up from 121 breakthrough deaths reported as of Sept. 8.

As of Friday 20,319 known COVID-19 deaths overall had been reported in Arizona.

CDC: Unvaccinated individuals have a fivefold higher risk of infection

Reports of breakthrough cases do not mean the vaccine doesn’t work, health officials have repeatedly emphasized.

“Vaccination against COVID-19 is the best way to prevent infection as well as hospitalization and death from the disease,” Herrmann wrote.

“The CDC recently published that unvaccinated individuals are at a five times higher risk of infection, more than 10 times higher risk of hospitalization, and more than 10 times higher risk of death when compared to vaccinated individuals.”

State and federal health officials also recommend that people who have been infected with COVID-19 get vaccinated. Among other things, scientific research hasn’t proven how long someone will be protected from getting COVID-19 after recovering from an infection.

The CDC cites emerging evidence that people get better protection by being fully vaccinated compared with having had COVID-19.

Some breakthrough cases could be because of waning immunity.

State and federal health officials are recommending certain high-risk people who received the Pfizer COVID-19 vaccine get a booster dose six months after their second dose.

“Studies have shown that protection from the COVID-19 vaccine may decrease over time and may be less able to protect against the delta variant,” Herrmann wrote.

“The purpose of the booster shot is to increase the immune response. At this time, the booster shot is only approved for those at high risk of contracting COVID-19.”

Breakthrough case data relies on matching up test and vaccine records, not on self-reporting.

State health officials match positive COVID-19 cases to vaccination records. They don’t rely on self-attestation or any kind of honor system as to whether someone with a positive case has been vaccinated.

The data has limits. The state’s matching system between positive COVID-19 cases and vaccination records may not be able to match records of someone who gets sick in Arizona but was vaccinated in Canada or in another state.

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Also, people who have been vaccinated may be more likely to access the health care system to get tested for COVID-19 in general than people who were not vaccinated, which could skew the percentages.

At the national level, the U.S. Centers for Disease Control and Prevention is only tracking cases of COVID-19 breakthrough cases involving hospitalizations and deaths. To date, 86% of the known COVID-19 breakthrough deaths nationwide have been in adults ages 65 and older, the CDC data shows.

Reach the reporter at or at 602-444-8369. Follow her on Twitter @stephanieinnes.

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