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As Japan plans to start booster shots of COVID-19 vaccines for people who have been inoculated twice, studies have shown that the efficacy of the vaccine tends to fall among older people and those who smoke and drink.

With over half of Japan’s population having completed their two shots, the government is looking at the possibility of making vaccinations a prerequisite for relaxing restrictions on activities, highlighting the importance of the efficacy of inoculations.

The National Hospital Organization Utsunomiya Hospital tested 378 staff members — who had received the Pfizer vaccine — for their antibody titer, or the amount and strength of neutralizing antibodies, three months after their second shots.

The test showed that vaccine efficacy decreases with age. Specifically, the median levels of antibody titer in people in their 60s and 70s and men in their 50s were only about half of those for people in their 20s. For women in their 50s, the levels stood at around 60% of those for people aged 20-29. The median levels for people who have not smoked were about 12% higher than those for all people tested, while the levels for past and current smokers were lower by some 23% and 35%, respectively.

“Older people may not be able to sufficiently maintain antibodies produced by vaccinations as their immune cells weaken with age,” said Kumiya Sugiyama, deputy head of the hospital in Utsunomiya, Tochigi Prefecture. “Many immune cells are in the lungs and directly connected to the immune system of the whole body, so smoking damages the immune cells in the organ, making it difficult to maintain antibody levels.”

A study of 1,774 staff members at Chiba University Hospital in the city of Chiba, who had completed their two doses of the Pfizer vaccine, found that the levels of antibody titer were higher among women and lower among older people, daily drinkers and those taking immunosuppressive drugs.

Compared with nondrinkers, the titer levels were little changed for people who drink two or three times a week, but were roughly 20% lower for daily drinkers.

“Older people and smokers are more likely to suffer from severe symptoms (of COVID-19),” said Takaji Wakita, head of the National Institute of Infectious Diseases. “It’s important (for such people) to actively get vaccinated even though the vaccines may not raise antibody titer levels significantly.”

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