For this study all students declared that they had been vaccinated according to the national immunization programs. Results showed nearly 20% of our students to measles, 36% to mumps, 6.6% to rubella, 12.5% to either diphtheria or tetanus were serologically susceptible and 46.5% showed evidence of immunity to pertussis (most possibly acquired by national pertussis infection). Moreover, in the absence of any history of respective vaccination,78% and 63.3% of HSS were protected to varicella and mumps infections, via natural infection. Study showed that relying on the past medical history of clinical disease to predict immunity status was not reliable.
In this study, nearly 63% of students were susceptible at least to one of the MMR agents. As these infections are transmitted via respiratory routes, they represent a high occupational risk for HCP/HSS, and for patients with whom they may come in contact(20-22).
Measles is a highly contagious viral infection which affects susceptible individuals of all age groups. Nosocomial transmission of measles is well documented, and may aid in the propagation of community outbreaks(6-8). Any community with less than 95% population immunity is at risk for an outbreak(20). Mumps and rubella are less contagious than measles, but outbreaks and nosocomial transmission of both infections may occur, and can results in a heavy financial burden on the healthcare facilities or have a considerable consequences(9,10,20-22).Therefore, all people who work in healthcare settings should be immune to measles, mumps, and rubella infections, documented by adequate immunization or laboratory evidence of immunity(1-4,20-22). MMR vaccination is the most effective preventive measure to protect HCP/HSS from acquiring these infections(1-4,20). The susceptibility rates to these infections are varied widely even within a country according to country's immunization practices, and time elapsed since the last dose of respective vaccine was administered(1-4,20). In This study, nearly 20%, 36%, and 6.6% of studied students were serologically susceptible to MMR agents respectively. There is no accurate information toward immunity status regarding to these infection among Iranian HSS. However, few studies in this regard were performed(23-27). The results were varied considerably: 52%(24)-to 88%(26) for measles, 64%(23)-to 76%(24) for mumps, and 96%(23)-to 100%(24) for rubella. Similar to these data and heterogeny in seroprevalence rates were also, observed worldwide(28-34). As are presented in the Table 5, the reported rates for measles were: 57%(28)-to 98%(33), for mumps: 68%(30)-to 92% (31), and for rubella: 83%(31)-to 97%(34). These variations could be explained possibly by difference in the national immunization program including implementation of some regional supplementary immunization activities, and the time elapsed since the last dose of the respective vaccine that was administered. Based on our data, regarding susceptibility to MMR agents and in accord with other reports(28,30,31), to provide a full protection against these viruses among Iranian HSS, universal MMR immunization is the most appropriate and cost-benefit strategy.
Varicella-Zoster (chickenpox) infection is endemic in the country, and the majority of Iranian children became infected to adulthood(35-37). Seroprevalence studies among Iranian general population indicated that seroprevalence rates were increased steeply from childhood: 22%(35)-to more than 86% and 98%(36) after the age of 30 years. Varicella is a highly contagious infection, and is transmitted via respiratory droplets, air-bornes, and direct contacts. Infection is preventable by active immunization. Because the high cost of the vaccine, and the usual benign course of the chickenpox during childhood, vaccination against varicella is not a public health priority in Iran, so, was not introduced in the national immunization programs. However, infection during adulthood is more severe and with the higher rates of complications, even death(38). Varicella nosocomial transmission and outbreaks has been reported(11). The number of studies that investigated the seroimmunity status among Iranian HCP/HSS are limited. However, as was observed in the general population, the seropositivity rates detected among HCP/HSS were varied greatly. While a 15% seropositivity rate was reported in one study from Shiraz(24), in other similar study this rate was 74.5%(39). As are presented in Table 5, similar to these variation, also were reported worldwide(28,20-34). Our data in this study are in parallel to that reported in Iranian population and nearly 78% of students as a results of natural infection were seropositive. Based on the data, if vaccine supplying was feasible, selective vaccination of susceptible students was the most appropriate and cost-benefit approach. Also, result showed that the past medical history of chickenpox was not a reliable tool to predict immunity status.
Diphtheria-Tetanus-Pertussis are vaccine preventable infections. Full immunization series along with high vaccination coverage rates during childhood associated with periodic booster injection is necessary to preserve vaccine- induced immunity on long- time against these agents. Diphtheria is a contagious and life-threatening disease. Recent diphtheria outbreaks in several countries indicated inadequate vaccine coverage. Also, outbreaks showed that the majority of the cases were adolescents and young adults(40,41).Tetanus remains an important public health problem in many parts of the world. It was estimated that every year nearly 58000 neonates, and unknown numbers of mothers dies from tetanus(42).In the year 2015, about 34000 newborns died from neonatal tetanus, a 96% reduction since 1988(43). Although, during recent years, the incidence of diphtheria, tetanus, and neonatal tetanus were very rare in Iran(44,45), seroprevalence studies results among general population indicated that nearly one-fourth of young adults were serologically susceptible to either infection(46,47). Our data in this study provide additional evidence to earlier findings(40-47), and indicated that more efforts should be made to achieve timely booster injection to preserve long-term immunity to both agents.
Pertussis is a highly contagious respiratory infection that is endemic in all countries. The disease is most serious in infants, and a significant cause of illness and death in this age group. Adolescents and young adults plays an important role in transmitting infection to unvaccinated/partially vaccinated infants. After reduction of pertussis following universal vaccination, the incidence of pertussis cases increased among adolescents and adults because waning of vaccinal immunity over time(48).Nosocomial outbreaks with substantial disruption and cost to hospital and HCP, and also morbidity, and even mortality in patients were reported. In most of these cases HCPs were the source(12,13,49-51).Similar to data that were reported in the world, during recent years in the Iran, also, the incidence of pertussis cases increased among infants and adolescents and young adults who had been vaccinated at childhood(52-55). Also, seroprevalence studies results showed that the rates of pertussis specific antibodies increased after the age of 9-10 years, an evidence of subclinical/atypical cases of pertussis among these age groups(53). For this study, nearly 46% of studied HSS were seropositive to pertussis infection, most possibly, due to pertussis infection during recent years. Similar to our finding also were reported from other parts of the country(47,54,55). For example; in a similar multi-center study among1617 university students with the mean age 19.6±2.1 years, this rates were 31.6%(55).
Our data and other mentioned evidences of infection(52-55), indicated that pertussis is active in the Iran. This resurgence of the infection is most probably due to waning of immunity induced by childhood immunization program(48). With the licensure of adult-typed acellular pertussis vaccine combined with diphtheria-tetanus toxoids (dTaP) for use in adolescents/young adults, now it is possible to preserve vaccine- induced immunity against DTP agents among older children/ young adults, particularly HCP/HSS by dTaP vaccination. The Advisory Committee on the Immunization Practices(56), and other authorities(1-4,48) recommended that all HCP/HSS regardless of their age should receive this vaccine booster dose as soon as possible. Although, there is no accurate information toward burden of pertussis disease/infection in Iran, our findings along with mentioned data indicated that pertussis infection act as an important pathogen among Iranian infants and adolescents, that may result to a major public health problem associated with a significant consequences. While considering the results of study conducted worldwide to evaluate the impact of adolescents dTaP immunization in reducing the burden of pertussis infection and its consequences(1-4,15,56,57), vaccination of our HSS with dTaP instead of dT seems most appropriate policy to provide protection against the DTP agents.
For this study some limitation did exist. The main limitation was its reliance to recall about history of vaccination and clinical compatible diseases. Also the relative small size was the other limitation.