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News Navigator: What are omicron vaccines, and should a patient get a shot after infection?

A still image from a video promoting vaccines targeting omicron variants created by the Japanese government is seen. (Image courtesy of the Cabinet Public Affairs Office)

The Mainichi Shimbun answers some common questions readers may have about vaccines for the coronavirus's omicron variants, which the Japanese government is promoting.

    Question: What kind of effects do the updated coronavirus vaccines have?

    Answer: The vaccines target omicron variants, which have become mainstream in Japan, but are called "bivalent boosters" as they also provide protection against the conventional strain. People aged 12 or older who have received their first and second doses are eligible for inoculation.

    Q: Should people who contracted COVID-19 in the past also get the bivalent boosters?

    A: According to the Ministry of Health, Labor and Welfare, those who have been infected in the past can also receive the bivalent boosters. When a person contracts the virus, they can acquire immunity, but it declines over time and they can become more susceptible to infections.

    It is believed that vaccines can further enhance the function of the immune system and reduce the risk of a second infection or severe symptoms. When a person has both natural immunity from infection and immunity from the vaccine, they acquire a high level of defense against the virus referred to as "hybrid immunity."

    Q: When should a person who got infected in the past get a bivalent booster?

    A: There are no rules for the omicron strain vaccines, which are mainly being used, and the health ministry states that people can receive the shots regardless of the period of time since infection. Although people must wait at least three months after their last dose, it is possible to be vaccinated immediately after an infection.

    Tetsuo Nakayama, specially appointed professor of clinical virology at Kitasato University, said, "It is believed that people's immunity gradually declines over several months after infection. It would be better to enhance their immunity by getting additional shots."

    Q: How effective are the updated vaccines and what side effects do they have?

    A: The health ministry says that the bivalent boosters are more effective than the conventional vaccines in preventing severe cases of the omicron strain and they are expected to be effective in preventing infection and the onset of symptoms, although it may be limited to a short period of time. Side effects such as fever and fatigue seem to be similar to those of conventional vaccines.

    (Japanese original by Takuya Murata, Lifestyle and Medical News Department)

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