How long between three-dose vaccinations is determined by the type of vaccine. Some of the vaccines that require three doses are some of the New Crown vaccines, HPV vaccine, Hepatitis B vaccine, DPT vaccine, and HIB vaccine, and most of them require an interval of 28 days or more. Most current three-dose forms of vaccines require at least 28 days between each dose. Although there is no data on the total interval time limit from the first to the third dose, it is recommended that the normal population should complete the full vaccination within 6 months. In addition, the optimal interval for HIB vaccine is 2 months, and the third dose also needs to be given 2 months apart to be effective. The DPT vaccine is effective when administered at intervals of 4 to 6 weeks starting at 3 months of age, as long as the vaccination is administered within this interval. When an acute disease occurs or when something happens and the vaccination cannot be given at the scheduled time, the interval can be extended, but care should be taken not to advance the vaccination so as not to affect the effectiveness of the vaccine. In the event of unusual circumstances such as illness or pregnancy, the vaccination schedule may be delayed, depending on the doctor’s instructions.