• Jiji

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The effectiveness of coronavirus vaccines declines over time, especially among older people, according to a survey by one Japanese city that covered 500 residents fully vaccinated against COVID-19.

The amount of antibodies that prevent infections declines significantly 90 days after receiving the second dose of a coronavirus vaccine, and the trend was notable among older people, the survey by the city of Soma in Fukushima Prefecture showed.

The results were based on blood tests of the surveyed residents aged between 12 and 89.

In May, Soma Mayor Hidekiyo Tachiya, also a doctor and chairman of the Japan Association of City Mayors, established the Soma City New Coronavirus Vaccine Medical Center, bringing together public health experts to verify the effectiveness and safety of COVID-19 vaccines and making proposals to the central government.

The survey focused on the levels of neutralizing activity, or ability to prevent infections, to examine the effectiveness of COVID-19 vaccines.

Between 30 and 90 days after the second dose, the median figure of neutralizing activity stood at 753 among people under 40. After 90 days or more, the figure fell to 106.

The median figure logged after 90 days or more came to 61 among people aged between 40 and 64, and stood at 44 among people aged 65 or over, the survey showed.

Many cases of so-called breakthrough infections, or infections among people who are fully vaccinated with two doses, are seen once the levels of neutralizing activity fall below 200, according to Masaharu Tsubokura, professor at Fukushima Medical University, who was involved in the survey.

Even if the effectiveness of preventing infections declines, the effects of avoiding severe COVID-19 symptoms are believed to last.

“We’re worried about an increase in the number of infection cases especially among fully vaccinated older people when a sixth wave of COVID-19 hits the country,” said Kenji Shibuya, former professor at King’s College London, who heads the vaccine medical center in Soma, underlining the need for early administration of the third shots of coronavirus vaccines.

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