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Researchers report that COVID-19 vaccinations provide an array of protection against the disease. Mixetto/Getty Images
  • A study from researchers in South Korea is the latest to report that people who are fully vaccinated have less serious cases of COVID-19.
  • Researchers reported that fully vaccinated people have milder symptoms and are less likely to end up in intensive care units if they are hospitalized with COVID-19.
  • They also reported there were few cases of pneumonia among vaccinated people who were hospitalized with COVID-19.

Fully vaccinated people who get “breakthrough” coronavirus infections can expect to have milder symptoms than those who are unvaccinated or only partially vaccinated, according to a new study.

Both clinical experience and CT scans suggest that full vaccination against COVID-19 strongly protects against severe disease, researchers reported in their study published Feb. 1.

The study involved 761 people hospitalized with COVID-19. Researchers found that 47 of them were fully vaccinated (6 percent), while 127 were partially vaccinated (17 percent) and 587 were unvaccinated (77 percent).

The findings mirror many clinicians’ real-world experiences with COVID-19 patients.

“Fully vaccinated people with a vaccine breakthrough infection are less likely to develop a serious illness than those who are unvaccinated and get COVID-19,” Dr. Sanul Corrielus, a Philadelphia-based cardiologist and the CEO of Corrielus Cardiology, told Healthline. “Even when fully vaccinated people develop symptoms, they tend to be less severe symptoms than unvaccinated people.”

“Patients that have had a full course [of vaccines] and/or booster tend to have much milder symptoms compared to unvaxxed individuals, especially if they haven’t had a prior COVID infection,” Dr. José Morey, an adjunct professor of radiology and biomedical imaging at the University of Virginia and Eastern Virginia Medical School, told Healthline. “If they have had a prior COVID infection, that also tends to have milder symptoms with or without vaccination.”

Researchers reported that when chest CT scans were performed on 412 of the study participants, the exams revealed 59 percent of those who were fully vaccinated were free of pneumonia — a serious complication of COVID-19 — compared with 30 percent of partially vaccinated participants and 22 percent of unvaccinated participants.

“Pneumonia is one of the worst manifestations of COVID and a leading symptom of hospitalizations, morbidity, and mortality,” Morey said.

“These findings augment what many other studies have shown us. Vaccinations are extremely effective in reducing moderate and severe COVID infections, hospitalizations, and mortality. This reduces the probability of developing pulmonary scarring and fibrosis, which we have seen in patients post-pneumonia [and] can be debilitating and life changing, particularly to young athletic patients,” he said.

Dr. Sachin Nagrani, the medical director at the telehealth company HEAL, told Healthline that CT scans can reveal inflammation resulting from COVID-19.

“The lungs contain many tiny blood vessels to allow for exchange of oxygen and carbon dioxide, and inflammation or damage to these small vessels can result in shortness of breath and potentially the need for ventilator support,” Nagrani told Healthline.

“It is reasonable to expect that vaccinated individuals on average will have less inflammation from COVID, which in turn leads to less progression to severe illness,” he said.

“Pneumonia, an infection of the lungs, is particularly severe with COVID due to the damage it causes to blood vessels within the lungs,” Nagrani added. “Developing pneumonia from any type of virus or bacteria can be deadly for people of all ages, and especially for the elderly or immunocompromised.”

Fully vaccinated participants were also less likely to need supplemental oxygen or a stay in the intensive care unit (ICU), according to the study, which was led by Dr. Yeon Joo Jeong of the Department of Radiology and Biomedical Research Institute at Pusan National University Hospital in South Korea.

More generally, the study found that the risk of severe COVID-19 was higher among older people as well as those with a history of diabetes, the blood disorders lymphocytopenia and thrombocytopenia, elevated lactate dehydrogenase levels, and elevated C-reactive protein.

Even fully vaccinated older people were more likely to get a severe breakthrough infection, but their risk was still lower than for unvaccinated or partially vaccinated people.

“Despite these differences, mechanical ventilation and in-hospital death occurred only in the unvaccinated group,” Jeong wrote.