May 12, 2022

Hokesen Letter, No 227 (English ver.), April 26, 2022
Health Care Center, Tokyo University of Foreign Studies
Yasuhiro Yamauchi, MD, PhD

Currently (late April 2022), the 6th wave of new corona infection has passed its peak, but the number of infected people remains high, and we are still required to live our lives while taking thorough measures to prevent infection on a daily basis. We believe that you have started a new school term "with corona", while also taking countermeasures against it throughout your life at the university.

New variants of COVID-19 have repeatedly mutated, resulting in global spread, but the Omicron remains the dominant variant (the BA.1 subvariant is being replaced by the BA.2 subvariant, which is more contagious). The Omicron variant is characterized by its high infectivity (transmissibility) and rapid doubling rate (easy multiplication) compared to conventional variants. On the other hand, the risk of hospitalization and severe illness is said to be lower with the Omicron variant than with the previous Delta variant. However, there is still a risk of severe illness in the elderly, people with underlying diseases, and people of all ages, and it can sometimes be fatal, so continued caution is required.

With regard to vaccines, it has been reported that immunization by initial vaccination alone is less effective in preventing the onset of Omicron variant infection. On the other hand, it has been reported that additional vaccination ( booster shot or 3rd dose) restores the effectiveness in preventing infection, disease onset, and hospitalization against Omicron variant infection, so a booster shot (3rd dose) is recommended.

At present, booster shot (3rd dose) is available for those under 65 years of age 7 months after the 2nd dose, or 6 months after the 2nd dose if there is availability in the reserved slots. Since the Omicron variant that is currently prevalent tends to be less effective than the conventional variant, the vaccine will be changed starting this May so that vaccination will be available 5 months after the initial vaccination. In Japan, the vaccination rate for the booster shot finally reached 50% in late April, and further dissemination of additional vaccinations continues highly desirable.

For the booster shot, regardless of the vaccine used for the initial vaccination, the mRNA vaccine (mix-and-match vaccine is also possible) is used, and its efficacy and safety have also been proven. Adverse reactions have been confirmed to be generally similar to those after the second vaccination, but the incidence of swelling of lymph nodes tends to be higher than that after the first vaccination (first or second shot). Also, those who had already been infected with COVID-19 can be vaccinated regardless of whether they received the initial or additional dose of the vaccine. For example, for those who have been infected after the initial vaccination, one of the guidelines for the booster shot is that 6 months must have passed and that a tentative interval of 3 months should be allowed between the infection and the additional vaccination.

Furthermore, in addition to the existing 「mRNA vaccines」 (initial and additional vaccination: Pfizer and Moderna) and 「virus vector vaccines」 (initial vaccination only: AstraZeneca), a new recombinant protein vaccine (initial and additional vaccination: Novavax) has recently been approved by the pharmaceutical affairs bodies. This vaccine is not yet in use at this time, but is expected to become available in the future. Since the mechanism and ingredients of this 「recombinant protein vaccine」 are different from those of conventional mRNA vaccines, it may be possible to inoculate even those who are allergic to mRNA vaccines, and it is expected that more people will be able to receive this vaccine.

Basic infection control measures against COVID-19 infections are also effective against Omicron variants, so it is important to continue with proper use of non-woven masks, hand hygiene, ventilation measures, etc., and to continue to take thorough infection control measures to avoid the 3 C's related diseases.

In the event of the appearance of symptoms that raise suspicions of COVID-19 infection, or in the event that a patient is to undergo testing for COVID-19 infection, or in the event that a patient has contracted COVID-19 infection, please report it using the University's 「Contact form for suspected infection with COVID-19」https://sanda.tufs.ac.jp/ emergency-contact/covid19/

If you have any questions, please consult with the Health Care Center, TUFS.


Coronavirus disease (COVID-19), National Institute of Infectious Diseases (Japan).

[ in Japanese] 新型コロナワクチンQ and A