People who contract COVID-19 after receiving two doses of a coronavirus vaccine have a far lower risk of becoming severely ill than unvaccinated patients, a major study by a Japanese medical institution showed Tuesday.
For patients age 65 or over, the percentage requiring treatment in an intensive care unit among those fully vaccinated when they became sick — or so-called breakthrough infection cases — was approximately one-seventh of that seen among unvaccinated people with the disease, according to the study by the National Center for Global Health and Medicine in Tokyo.
The percentage of deaths among fully vaccinated, older patients was roughly a third that of unvaccinated people, the study showed.
The study included 3,417 people who were admitted to hospitals across Japan in July or later and reported to the national center by Sept. 22. Of them, around 90% had not been vaccinated or had received only one dose.
Of the 2,574 people who had clear records of their vaccination date, 54 people, or 2%, became infected with the coronavirus at least two weeks after the second dose, which is considered the time required for the vaccine to become fully effective.
Among the group, 44 were older people and a lower percentage of them showed symptoms such as a fever and cough than was seen among unvaccinated people and people who had received only one COVID-19 vaccine shot.
Two of the cohort died — a woman in her 80s and a man in his 60s — but both suffered underlying health conditions such as heart failure and high blood pressure.
Looking at the treatment of older patients by vaccination history, 16.3% of unvaccinated patients required ICU treatment, compared with 2.3% of breakthrough (vaccinated) patients.
The death rate was 14.7% among unvaccinated older people, compared with 4.5% among breakthrough patients. The share of fully vaccinated older people requiring oxygen inhalation was roughly half that of unvaccinated patients.
"The study shows, once again, that while COVID-19 vaccines tend to lower the risk of developing severe symptoms, there are a certain number of breakthrough infection cases," said Nobuaki Matsunaga, a senior official at the national center. "As many hospitalized patients have not been fully vaccinated, people need to take extra caution until they have completed their second dose," Matsunaga said.
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