As the new omicron variant continues to spread throughout the United States, vaccinated people who are older or sicker are at greatest risk of hospitalization from a COVID-19 breakthrough infection, according to a new analysis by the Kaiser Family Foundation.
But the shots continue to offer some protection, because these breakthrough illnesses are shorter and milder than sickness in unvaccinated people, the study found.
“It tells us the older people and people with high-risk preexisting conditions should continue to be cautious about COVID, especially given the new variant,” said study author and public health expert Cynthia Cox, vice president of the Kaiser Family Foundation.
“Even though these hospitalizations do happen, the vaccine is providing a significant amount of protection for people,” she added.
Much is still unknown about why certain vaccinated people end up in the hospital with COVID-19. With growing evidence of waning immunity and breakthrough infections in fully vaccinated individuals, experts have tried to answer this question: How well do the shots prevent severe disease and hospitalization?
This new study is the first close look at the characteristics of vaccinated people who get very sick — and their hospital experience, once admitted. Conducted by the Kaiser Family Foundation and health care software company Epic Systems, it’s based on an analysis of electronic medical records of 120,000 patients hospitalized in 250 hospitals across all 50 states between June and September.
The research was conducted prior to the new variant omicron’s detection and before the availability of a booster dose, but the clinical course of these “breakthrough” experiences is likely to be similar, said Cox.
“Older people have weaker immune systems,” Cox said, “and the vaccine is not as effective for them as it might be for a younger person.”
Public health experts continue to believe that breakthrough infections are relatively uncommon and rarely result in hospitalizations. Of all hospital admissions for COVID-19, the vast majority (85%) were in people who were unvaccinated, according to the new study.
But more cases among the vaccinated are expected in the future. Compared to the delta variant, which is still prevalent in the U.S., omicron is better able to dodge some vaccine-induced immunity. In this study, many people had been vaccinated more than six months earlier and might have experienced a reduction in immunity.
The analysis found that more than two-thirds (69%) of breakthrough COVID-19 hospitalizations occurred among people ages 65 and older. A fifth (21%) occurred among people ages 50-64. Only 10% occurred among younger adults. In contrast, the majority of people who were not fully vaccinated and hospitalized with COVID-19 were under the age of 64.
Vaccinated adults hospitalized with breakthrough COVID-19 — whether young or old — were more likely to be living with chronic health problems such as hypertension, diabetes, heart failure or chronic obstructive pulmonary disease.
But these patients were less likely than unvaccinated people to suffer from the most severe consequences of COVID-19, such as pneumonia or respiratory failure. They were also less likely to need ventilator support or treatment with the anti-inflammatory drug dexamethasone.
And their hospital stays were shorter. The median stay was 5.6 days for elders who were fully vaccinated, compared to 6.7 days for people who were unvaccinated or partly vaccinated.
“That suggests that even though these people are landing in the hospital due to COVID, their severity of disease appears to be lower,” said Cox. “So the vaccine is still helping them.”
That’s likely because T cells — a type of white blood cell that plays an important role in the human immune system — in vaccinated people can mount a robust defense against the virus. Despite a breakthrough infection, T cells appear to help prevent severe disease.
Since the beginning of the pandemic, elders and the chronically ill have been the most hard hit[.
“The problem is that the majority of this (elder) population has chronic diseases,” said Los Altos geriatric specialist Dr. Mehrdad Ayati. In December, about 12 to 15 of his patients in skilled nursing facilities have been hospitalized with breakthrough infections. All were vaccinated, and many were boosted.
They’re more vulnerable to all pathogens, not just SARS CoV-2 breakthrough infections, he added. “With any infection, COVID or not COVID, they have the higher tendency to be hospitalized,” he said.
When elders are infected, “other medical problems flare up,” Ayati said. “For example, if they have heart problems, heart failure is going to start to manifest. If they have diabetes, it’s more likely to be uncontrolled.”
In addition, elders are less able to control the virus. During aging, the immune system changes in two major ways. One is a gradual decline in immune function called immunosenescence, which hampers the recognition and clearance of a pathogen. The other change is greater risk of inflammation called inflammaging, which arises from an overactive yet ineffective alert system.
The study reinforces the need for elders and the chronically ill to take additional precautions, she said.
“Even if they are vaccinated, that’s going to mean getting a booster shot as soon as possible,” restoring antibody levels, said Cox. “Maybe wearing a mask in public. And just being conscientious about gathering large groups of people indoors.”