https://orcid.org/0000-0002-3135-1757
ABSTRACT
Limited data are available regarding the seroprevalence of measles, mumps, rubella, and varicella (MMRV) among emergency medical technicians (EMTs) in Japan. The present study aimed to review a project to evaluate adequate immunity against MMRV for the requirement of additional vaccination among EMTs in accordance with the Japanese Society for Infection Prevention and Control guidelines. A retrospective observational study was conducted as part of a vaccination program for EMTs. Each participant was evaluated for medical history, vaccination history, and serology using the criteria established by the Japanese Society of Infection Prevention and Control. In total, 85 EMTs (median age, 31 years; male, 92.9%) were included. Among the included EMTs, 32 (37.6%), 54 (63.5%), 46 (54.1%), and 84 (98.9%) were seropositive for measles, rubella, mumps, and varicella, respectively, whereas 1 (1.2%), 6 (7.1%), 5 (5.9%), and 0 (0%) were seronegative. Furthermore, 48 (56.5%), 27 (31.8%), 45 (52.9%), and 8 (9.4%) EMTs received an additional dose of vaccines for measles, rubella, mumps, and varicella, respectively. The present study suggests that EMTs are not fully immune to MMRV, which highlights the need for confirming the immune status and additional vaccination requirement to prevent occupational infections.
Confirming adequate immunity against measles, mumps, rubella, and varicella (MMRV) is recommended for all healthcare workers (HCWs). The Japanese Society of Infection Prevention and Control (JSIPC) has established vaccine guidelines for HCWs in 2009, with subsequent updates published in 2014 and 2020.Citation1,Citation2 Although several studies have evaluated the seroprevalence of MMRV among hospital-based HCWs in Japan,Citation3–5 few have focused on the seroepidemiology of MMRV among emergency medical technicians (EMTs).
The Fire and Disaster Management Agency (FDMA) in Japan had published their “infection prevention manual for emergency medical technicians” in 2019, which was updated in 2020.Citation6,Citation7 This manual recommends vaccinations against MMRV, tetanus, and hepatitis B and serology check when needed according to the JSIPC guidelines. Because of a reported case of a paramedic getting infected with measles during the transport of an infected patient,Citation8 it is evident that EMTs working as front-line HCWs are at high risk of acquiring contagious diseases and should, therefore, be prioritized for adequate vaccination. In 2020, our hospital initiated a project to confirm adequate immunity against MMRV and the requirement of additional vaccination among EMTs at fire stations in Narita, Japan. The present study aimed to review this project and describe the seroepidemiology of MMRV among EMTs.
This retrospective observational study was performed as part of a vaccination program for EMTs that included paramedics at the Japanese Red Cross Narita Hospital. The hospital collaborated with all eight fire stations in Narita, a middle-sized city in Japan with an approximate population of 131,000, to confirm the immunity status of their EMTs against MMRV and arrange for vaccinations when needed. The project was conducted from August to November 2020. All participants completed a questionnaire distributed in advance that collected data on their medical history and past immunization against MMRV; they were then requested to submit a written vaccination history. Antibody titers against MMRV were measured using an enzyme immunoassay (EIA) kit (Denka Seiken, Tokyo, Japan), with positive and negative cutoff values of ≥4.0 and <2.0, respectively, as determined by the manufacturer. Determining the immune status and performing additional vaccinations were in accordance with the JSIPC guidelines. EMTs who submitted a documented history of two vaccinations were not required to receive any vaccine regardless of their antibody titer. Those who submitted a documented history of one vaccination required one additional vaccination regardless of their antibody titer. MMRV IgG EIA values of <2.0 indicated a negative antibody titer. In contrast, IgG EIA values of ≥16.0, ≥8.0, ≥4.0, and ≥4.0 indicated positive antibody titers for measles, rubella, mumps, and varicella, respectively. EMTs with antibody titers that did not fall into any of the categories were recommended to receive an additional dose of vaccine. This study was approved by the ethics committee of the Japanese Red Cross Narita Hospital under the condition that the confidentiality of all personal data be maintained (JRCNH-728-01). All participants of the vaccination program were included in the present study. Data on age, sex, medical history, and vaccination history with a written document were collected from the completed questionnaires. Vaccination histories were validated using the submitted copies of maternity health-record books or documented records issued by hospitals. In the statistical analysis, categorical variables were described as numbers and percentages, whereas continuous variables were described as medians and ranges.
In total, 85 EMTs, including 46 paramedics, were included. details the demographic characteristics of the participants. Participants had a median age of 31 years, and 79 (92.9%) were male. The dominant age group was 21–30 years (44.7%). summarizes the participants’ medical history, documented vaccination history, seroprevalence, and additional vaccinations. Among the included participants, 16 (18.8%), 16 (18.8%), 41 (48.2%), and 54 (63.5%) reported that they have had measles, rubella, mumps, and varicella, respectively. Of the participants, >50% either had no history of vaccination or could not provide documents regarding the history of vaccination against MMRV. Moreover, 16 (18.8%), 17 (20.0%), 0 (0%), and 1 (1.2%) participant were vaccinated twice for measles, rubella, mumps, and varicella, respectively. Among the participants, 32 (37.6%), 54 (63.5%), 46 (54.1%), and 84 (98.9%) had positive antibodies for measles, rubella, mumps, and varicella, respectively. Furthermore, 1 (1.2%), 6 (7.1%), 5 (5.9%), and 0 (0%) participants were seronegative for measles, rubella, mumps, and varicella, respectively. Notably, five of six participants seronegative for rubella were males in their 40s. Additional measles, rubella, mumps, and varicella vaccinations were required for 48 (56.5%), 27 (31.8%), 45 (52.9%), and 8 (9.4%) participants.
Table 1. Participant demographic characteristics (N = 85)
Table 2. Past history, documented vaccination history, seroprevalence, and additional vaccination (N = 85)
The results from our present study indicated that approximately 50% EMTs required at least one additional dose of vaccine for measles, rubella, and mumps according to the JSIPC guidelines, with some being fully susceptible to measles, rubella, and mumps.
EMTs may have lower seropositivity for these contagious diseases than hospital-based HCWs. Seropositivity within a specific population can be affected by age and sex distribution; young and middle-aged men, the population that represents the majority of EMTs across Japan, tend to have lower seropositivity. According to statistical data from the FDMA, only 3.5% of all EMTs are females.Citation9 Using the same cutoff, a previous study showed that 62.2%, 80.3%, and 68.2% of hospital-based HCWs at a hospital in Japan exhibited seropositivity for measles, rubella, and mumps, respectively,Citation5 which were higher than the values (37.6%, 63.5%, and 54.1%, respectively) observed in the present cohort. This difference can be attributed primarily to the fact that majority of our participants were young and middle-aged men compared with the female-dominant population with a wide range of age distribution included in the aforementioned study. This is also supported by the lower seropositivity for measles and mumps among individuals in their 20s–30s included in the aforementioned study. Moreover, data from the Japanese National Institute of Infectious Diseases revealed that the seroprevalence for rubella among men in their 40s and 50s were lower than that in women of the same age owing to the precepts of the national vaccination program conducted during the time when they had received the rubella vaccine.Citation10
Notably, vaccination history and seropositivity among individuals are affected by the changes of the national immunization program (NIP) in Japan. The measles and rubella vaccines were first introduced in 1966 and 1976, respectively, in Japan and became a part of routine vaccinations included in the NIP in 1978 and 1977, respectively. At this point in time, the rubella vaccine was administered only to female junior-high school students. The combined measles, mumps, and rubella vaccine, which was introduced to the NIP in 1989, was withdrawn in 1993 owing to aseptic meningitis as a side effect. In 2006, the two-dose schedule using the combined measles-rubella vaccine was implemented for universal immunization.Citation11–13 Since 2019, the Japanese government has started examining the levels of rubella antibody to determine the immunity status of adult males and provide the measles-rubella vaccine free of cost to susceptible males born between 1962 and 1979.Citation14 We found that some participants in the present study had received follow-up doses either independently or as part of the additional immunization campaign. The live attenuated varicella vaccine derived from the Oka strain, which was developed in 1974, was administered on a voluntary basis in Japan until 2014; at this point in time, it was introduced into the NIP for universal immunization by the government.Citation15 In contrast, the mumps vaccine has been offered on a voluntary basis till date.Citation16 The relatively higher rate of vaccination history against measles and rubella among younger individuals and the lower rate of vaccination history against mumps and varicella zoster virus among the individuals in all age groups in the present cohort also reflect this historical background. Moreover, the unique cohort of this study, which comprised primarily males and included a large number of middle-aged male EMTs, is more susceptible to measles and rubella because they had fewer opportunities to receive measles and rubella vaccine doses in the NIP.
The present study suggests that appropriate vaccination programs should be developed for healthcare students during or even before pre-occupational education. In the United States, the majority of healthcare professional schools require their students to receive these vaccines before admission.Citation17 However, such strict requirements are rare in Japan. In addition, the majority of the study participants could not provide a documented history of vaccination against MMRV and some were fully susceptible to MMRV, which suggests that no screening was performed at their occupational institute. In addition, each person should receive a vaccination record, which should then be preserved permanently. Ideally, systems for maintaining electronic records of vaccination should be implemented.Citation18 Guideline-compliant vaccination programs for EMTs are strongly encouraged for their as well as their patients’ safety.
The present study has some limitations. First, the sample size was small and may thus not reflect the general population of EMTs in Japan. However, considering that the female ratio in this cohort is higher than that in the general population, sex distribution may not cause bias for lower seropositivity in our cohort. Second, regionality could not be considered in this study because all EMTs were stationed at fire stations within one city. Third, no consensus has been established regarding the higher antibody titer used as the cutoff for seropositivity, with evidence showing that the effectiveness of higher titers in HCWs was inadequate.Citation4 However, these criteria were used based on the fact that both the JSIPC and FDMA recommend them. Moreover, we compared the data obtained from this cohort with those reported in a study that used the same criteria.Citation5
In conclusion, this retrospective descriptive study suggests that EMTs in Japan are not fully immune to MMRV. Thus, promoting guideline-compliant vaccination programs for EMTs and the students of healthcare professional schools is strongly recommended to prevent occupational infections.
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References
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