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The two main COVID-19 vaccines in use in the US may not prevent the rare, “breakthrough” infection — but even in those cases they reduce the severity of the disease, according to landmark study by researchers from the University of Arizona Health Services.

The Moderna and Pfizer vaccines provided better than 90% protection against infection in a study involving 4,000 people — mostly Arizona health care workers and first responders.

Moreover, the vaccine cut in half the course of the illness and reduced serious symptoms by 58%, the researchers concluded.

The study comes in the wake of a recent “superspreader” event at a White Mountain Community Dance Hall, were a reported 22 out of 70 people got infected with COVID-19, including nine people who had reportedly been partially or fully vaccinated. Navajo County and state health officials have not confirmed the infections, but have launched a contact tracing effort based on media reports of the incident. Several of the people were hospitalized and one has reportedly died.

The latest Arizona study supports other research showing the vaccines prevent infection and serious illness. That’s crucial in the face of the rapid spread in Arizona of the Delta variant, which devastated India. Other studies suggest the Pfizer, Moderna, AstraZenica and Johnson and Johnson vaccines still work against the Delta variant, especially when it comes to preventing hospitalization and death.

The UA Health Sciences study followed 156 unvaccinated, 11 partially vaccinated and five fully vaccinated people who developed an infection, according to the research published in the New England Journal of Medicine.

Dr. Jeff Burgess, associate for research, said, “If you get vaccinated, about 90% of the time you’re not going to get COVID-19. Even if you do get it, there will be less of the virus in you and your illness is likely to be much milder.”

The messenger RNA Moderna and Pfizer vaccines present the immune system with the spike protein the virus uses to infect cells. This triggers an immune system response that prepared the body’s defenses for an encounter with the actual virus.

Even one dose of the two-shot vaccine reduced viral loads by 40% compared to people who didn’t get vaccinated. Viral load plays a key role in the severity of disease.

In vaccinated people who got infected, the virus was detectable for only a week. In the unvaccinated, the virus remained circulating in the system for two weeks or longer. Among the vaccinated, the risk of developing a fever or other more serous systems dropped by 58%.

The study found that a single dose of the vaccine provided 81% protection against infection and the second dose boosted protection to 91%.

The university researchers relied on $7 million in federal funding for their ongoing AZ HEROES study and has just received a second year of funding.

“We are seeing the same high levels of vaccine effectiveness, so we feel good about that,” said Dr. Burgess. “But more importantly, we’ve added a number of measures of the severity of infection among individuals who have been vaccinated as a comparison to those who haven’t and we measured how much of the virus there is and for how long.”

Research team member Karen Lutrick said, “we really appreciate the participation of all our AZ HEROES and RECOVER participants, because without them and their work — we wouldn’t have this information to share.”

To learn more about the study and the ongoing effort to recruit participants go to

The study underscores the power of the vaccines, just as a lag in the state’s vaccination campaign and the rapid spread of the new, more dangerous Delta variant has alarmed public health officials.

The Delta variant now accounts for a quarter of the cases in the US and is spreading rapidly in Arizona. First identified in India, the Delta variant is likely twice as infectious as the original strain identified in Wuhan China. Some evidence suggests it also causes more serious illness and may more easily infect children. A recently identified “Delta Plus” strain may also prove more resistant to front-line treatments like the use of monoclonal antibodies.

One study in the medical journal Lancet suggested the hospitalization rate among people infected with the Delta strain was 85% higher than other strains.

Fortunately, the current vaccines appear highly effective against the Delta strain. Two doses of the Pfizer vaccine proved 96% effective in preventing hospitalization in people infected by the Delta strain, according to a preprint study by Public Health England. Even a single dose of the Pfizer vaccine proved 92% effective in preventing hospitalization.

The Moderna vaccine is expected to have similar impact and the AstraZenica and Johnson and Johnson vaccines only slightly less effect.

The studies suggest the Delta variant is more likely to cause a “breakthrough infection” among those vaccinated, even if it doesn’t result in hospitalization.

As a result, health officials have redoubled their appeal to people to get vaccinated.

After weeks of sustained decline, cases in the US have risen by 5% as a daily average over the past two weeks, according to CDC data compiled by the NY Times. ( The US is reporting about 12,000 new cases daily and about 200 additional deaths.

In Arizona, cases have been rising for weeks, including a 14% increase as a daily average over the past two weeks. The state is reporting about 500 new cases daily – with a per-capita infection rate of about twice the national average.

Nationally, 47% of US residents are fully vaccinated compared to about 43% in Arizona — leaving the state and the nation far from the relative safety of “herd immunity.”

Navajo County remains one of the state’s hot spots, despite a 10% decrease in daily cases over the past two weeks. The county has 13 new infections per 100,000 as a daily average — nearly twice the statewide average.

Apache County has seen a 14% decline in new daily cases over the past two weeks as a daily average to 5 per 100,000 — below the state average.

On the other hand, Gila County has experienced a flareup. Cases have increased by 25% to 8 per 100,000 — just above the state average and twice the national average.

Some 48% of Navajo County residents, 58% of Apache County residents and 45% of Gila County residents are fully vaccinated.

Peter Aleshire covers county government and other topics for the Independent. He is the former editor of the Payson Roundup. Reach him at

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