Cases of so-called breakthrough infections, in which fully vaccinated people test positive for the coronavirus, are being reported across Japan.
Researchers at the National Center for Global Health and Medicine analyzed data on around 3,400 patients who were hospitalized at some 600 medical institutions nationwide from July this year through last Wednesday.
They found that 2,456 of them were unvaccinated, 654 had received one shot and 307 had received their second shot.
They determined that 54 patients were breakthrough cases, as they were hospitalized with symptoms more than two weeks after their second shot. Forty-four of them were elderly.
The researchers found that elderly breakthrough patients were at lower risk of becoming seriously ill compared to the unvaccinated.
The number of the elderly patients who needed oxygen was half that of the unvaccinated. The number of those treated in intensive care units was one-eighth, and that of those who died was one-third.
Matsunaga Nobuaki, who analyzed the data, says it appears that vaccines prevent serious illness, but a closer look is needed.