Dear Editor, The new available coronavirus disesae COVID‑, 19 vaccine becomes the new hope for the control of the disease. A recent report showed that the vaccine could induce protection in a large group of vaccinated subjects. With the rapidly increasing demand for the COVID‑, 19 vaccine, the supply is usually insufficient and the price of the vaccines becomes greatly different among different buyers. At present, there are many brands of the COVID‑, 19 vaccine with different cost‑, effectiveness properties. Sometimes, it takes a long time to get a sufficient amount of COVID‑, 19 vaccine supplied by a manufacturer. There is a new idea for vaccine brand mixing—, different vaccine brands in different doses. As noted by Public Health England, this should be on extremely rare occasions. To date, there are no data from the trial on the newly proposed ideas. However, it might be roughly predicted using a medical mathematical prediction. Here, the authors focus on the three different available vaccines for the switching model. . .