Results showed that all participants were immunized against HB infection, but nearly 16% of them did not complete their vaccination course. Study showed that all participants were immunized against HB, but nearly 16% of them did not complete their vaccination course. However, a minority of vaccinees performed PVST. Most of studies HCPs were young in their age and work. Based on our data, 83% of studied subjects were serological immune to HBV infection, 0.78% and 4.6% showed evidence of chronic and resolved HB infection, respectively. Although 12% of vaccinated personnel were serologically susceptible to HBV, most of them retained their specific immune memory demonstrated via response to a HB vaccine booster dose injection. The prevalence rate of anti-HCV was low. Finally, study results indicated that more than 42.4% of HCPs experience at last one NSIs in their work within the preceding year.
Based on this study findings most studied personnel were fully vaccinated. This proportion is one of the highest rates of vaccination coverage among HCP with the reported prevalence in Iran [22, 23] and other countries [19-21 17-20, 24-27]. The reported rates of HBV immunization in HCP from both developed and developing countries varied widely [19-21 17-20, 24-27]. Whereas, only 11.4% of Cameroonian HCP were fully vaccinated against HB , and nearly all surgical nurses in Polish hospitals were immunized [27 20]. The self-reported rates of complete vaccination detected in national survey was 63.4% in the United States of America [20 18], 55.4% in India , and 60% in China . However, this rate was 85-93% 100% among health care providers working in different European Union countries [21 19,20]. Similar to our findings, during recent years relatively high rates of immunization against HB in HCPs working in hospitals, from different regions of Iran were reported [22, 23]. In this regard, to estimate the HB vaccination coverage rates among Iranian HCP two systematic reviews and meta-analysis were conducted [22, 23]. In the first study , 6,311 subjects from 21 articles were included. The history and the complete vaccination rates were estimated to be 86.9% and 70.3%, respectively . The second one, performed among 4,104 Iranian physicians and nurses, showed that the history and full HB vaccination rates were 88.7%, 93.5% and 73.1%, 76%, respectively . The most possible explanation for the higher rates of HB vaccination coverage in Iran may be due to easy access to free HB vaccine in the hospitals across the country. In addition, the important roles of the occupational health promotion and infection prevention/control committee established in most hospitals should also be considered.
Our data showed that only a minority of surveyed subjects (<5%) checked their anti-HBs titers on the recommended schedule. The probable reasons for this rate could be explained as follow: 1) The employees should be charged for PVST, which is a rather expensive test, 2) Many of them believe that vaccination is associated with full immunity, so they feel no requirement for PVST. Actually it appears that most HCPs do not have enough or accurate information about PVST. However, during their work’s experience, 155 (20.23%) nearly 20% personnel did anti-Hbs serological testing as part of their post-exposure management. After HBV vaccination, serological testing to document immune response is recommended for persons whose post-exposure clinical management depends on the knowledge of their immunity status. However, the global rates of post-vaccination serotesting varied greatly and the majority of the vaccinated HCP did not check their anti-HBs levels after vaccination [24, 28-31 27-30]. Despite applying PVST in the vast majority of EU countries, serologic testing rates were markedly different among these countries [21 19]. For example, data from a large teaching hospital in France showed that 65% of vaccinated personnel tested their anti-HBs antibody on completion of immunization [21 19]; whereas, this rate in a multicenter study in Poland was 24.9% . Similarly, in a study on medical students from São Paulo in Brazil, out of 675 participants, 48.9% were fully vaccinated and only 34.8% of vaccinated subjects performed antibody testing [31 27]. Based on our data and the literature results, particular attention should be given to post-vaccination antibody testing to ensure that vaccinated personnel at risk have developed adequate immunity against HB infection. Therefore, it seems reasonable that testing of antibody on completion of vaccination should be incorporated into a vaccination program on a mandatory basis.
The results from several long-term follow-up studies on the HB vaccinated people indicated that the vaccine-induced antibody concentration declined with time and could reach to non-protective or even undetectable titer without further booster injection or subclinical breakthrough HB infection, 15-23 years after the initial immunization [32-3431-33]. Based on our survey study, protective antibody titers remained in 83% of the screened participants many years after the primary course of HB vaccination. However, study showed that 93 out of 766 (12.0%) of HCP were boosted with ≥1 dose of HB vaccine during their professional career. This high-rate of seroprotection may be due to the younger age of personnel (mean age 33, years), shorter time elapsed since the primary course of vaccination (46.5% of them had work’s experience of fewer than 10 years), furthermore 12.0% received an additional dose of HB vaccine, occurrence of subclinical breakthrough infection in 4.6% of them, and development of natural boosting in nearly 144/766 (18.78%) 19% of subjects during their career).
Based on our arbitrary definition for this study, 144 persons showed evidence of natural boosting during their profession. The prevalence of natural boosting varied in different settings across the world, obtained from long-term prospective studies. In a 20-year follow-up study on immunized children born from HBsAg positive mothers, the reported rate of natural boosting was 5.93% . The rates reported in a 22-year prospective study on native Alaskan people was 27% , and 23% in a 23-year follow-up study in China . However, this rate in our earlier cross-sectional study on young adults vaccinated in infancy in Mazandaran Province was 19% . The mechanism of natural boosting was uncertain. However, it may result from a cross antigen reaction or from a transient HB viremia with no other evidence of HB infection. This phenomenon possibly leads to maintaining long-term immunity and memory against HB infection .
In this study, 0.78% and 4.6% of studied subjects were HBsAg and anti-HBc positive. These rates were not significantly different among those who were fully or incompletely vaccinated and also there was no correlation with their work’s experience. The frequency of HB infection in HCPs depends on the HBsAg prevalence in the general population where they work and the frequency of exposure to B/BF in their career [7-126-11]. Therefore, the reported prevalence varied considerably among HCPs working in different countries, and even within the same country. More than two decades after successful implementation of the universal infantile HB immunization along with HB vaccination of the high-risk groups and adolescents catch-up immunization program in the world and Iran, the prevalence of HB infection and HBsAg carrier reduced significantly among general population and some high-risk groups including HCP in the many countries and even within the same country in the world [3,372,36]: 0.3% (0.15-2.7) in USA , 0.9% (0.1-4.4%) in EU , 1% in India , 4.7% in Indonesia , and 8.7% (5.2-14.3%) in Cameron . The prevalence of HB infection in Iran reduced in line with its global downward trend [41,4240,41]. In this regard, the national prevalence of HBsAg and anti-HBc positive cases was estimated to be, respectively, 1.84% (95%CI: 1.61-2.09) and 13.59% (95%CI:12.92-14.29) in the range of 0.76%-5.10% and 4.17%-36.9% . The frequency rates of HBsAg and anti-HBc in this study were lower than those reported in Iranian general population. It was similar to our recent findings from other teaching hospitals in Mazandaran Province, and some other parts of the country [43,4442,43]. However, the prevalence of HBsAg positivity in this study was higher than that the recent estimate among Iranian HCP: 0.4% (95%: 0.1-0.5) in the range of 0.3% and 4.1% . Results showed that 4.6% of screened vaccinated personnel were anti-HBc positive, which in the majority of cases was associated with protective titers of ant-HBs antibody suggestive for resolved subclinical (breakthrough) HB infection. The frequency of positive rate was not significantly different among different profession. Symptomatic HB infection or HBsAg carrier status, following a successful HB immunization of HCP, was rare [7-96-8]. However, the reported prevalence of subclinical breakthrough HB infection in fully vaccinated HCP varied widely in the world. For example, the incidence rates were, respectively, 2.5%, 2.5%, and 2.5% in the USA , Spain  and Japan  versus 16.4% in Poland , 24.7% in India , and 70% in Albania . The relatively low prevalence of HB infection reported in this and some other domestic studies could be attributed to the high rate of vaccination against HB among Iranian HCP [22, 23]. However, the role of the National Infants HB Immunization Program launched in 1993 in reducing the prevalence of HBsAg among Iranian population should not be ignored [41,42 40,41].
According to our findings, approximately 12% of the vaccinated persons were serologically susceptible to HB infection. Three to six weeks after administering one dose of HB vaccine, 72 out of 78 91% of boosted subjects responded and seroconverted, indicating the presence of long-lasting protective immune memory from the vaccination.
None of the international guidelines for HB immunization has recommended a routine administration of booster doses of HB vaccine or periodic anti-HBs antibody testing once the response to a full vaccination occurred in general, but special consideration for high-risk groups may be worthwhile . HCP are regarded as a high-risk group to HB infection. Therefore, booster vaccination is strongly recommended for non-immune HCP, regardless of endemicity in the area concerned [7-9,16-18,and 50 6-8, 14-16, and 49]. A recent Cochrane review was not able to identify any randomized study to assess the benefit of booster vaccination in preventing HB infection . However, periodic anti-HBs testing is recommended in some European countries . Some authorities [52,53 51,52] also recommended booster injection to serologically susceptible persons [14,21,24,52,53 19, 24, 51, 52]. Our findings support the idea that no booster of HB vaccine is required after a successful primary vaccination. These findings are consistent with data published recently. The result from a long-term study, 10-31 years after the initial HB immunization on HCP, indicated that none of the participants was HBsAg positive, 2.5% of them showed evidence of resolved HB infection during their work’s experience, and approximately 23% of them had lost their seroprotection. After boosting, more than 94% of serosuseptible participants were seroconverted. Researchers concluded that HB vaccine provides long-term protection and thus booster vaccination is not necessary . However, further studies in this area are still required. Nevertheless, highly infectious HB virus inoculum might overpower low/non-protective anti-HBs titers during the long professional life of HCP. In these situations, the administration of a booster dose of HB vaccine could be considered [7-9,16,17,46,53 6-8, 14,15, 45, 51,52].
This study showed that 0.91% of HCP were anti-HCV antibody positive. However, none of the PCR tested subjects were positive. This may be due to clearance of HCV infection by somebody, EIA test or HCV PCR were falsely positive, and rarely that a person has intermittent or low level viremia. The prevalence of HCV infection varied markedly among different countries in the world. While central and East Asia, North Africa and the Middle East estimated to have high prevalence of infection rates (>3.5%), most EU countries and Australia showed the prevalence of 1.5-3.5% and some other countries, including the most American countries, had the prevalence of less than 1.5%. During recent years, an upward trend of HCV infection was observed in the world [4-6 4] and in Iran . However, the prevalence of HCV infection in Iran seems to be as low as 0.3-0.5% among blood donors [55,56 54,55]. In this study, the prevalence of anti-HCV antibody positivity was higher than those Iranian blood donors. Although, the risk of HCV infection, following occupational exposure, was not high [12,15 10,11,14], nearly 1% of the prevalence rate found in this study indicated the necessity of appropriate post-exposure management in the cases of exposure to possible infectious sources. In this situation, regular follow-up evaluations are needed to diagnose possible HCV infection for early treatment [8-9 9-11]. However, because of low rate of HCV infection among the general population in Iran, pre-exposure screening of HCPs for HCV infection is not recommended.
Potential limitation of this study was its reliance on self-reported data, which might influence the reliability of the findings and cause probable recall bias. Another limitation was the lack of information about immune responses to the initial HB immunization course in the majority of screened personnel. The key strength of the present study was the inclusion of various professional groups of HCP working in various hospitals in four large cities, which made the result more generalizable among HCP.
For this study some limitations did exist. The most potential limitation was its reliance on self-reported data, which might influence the reliability of the findings and cause probable recall bias. Other limitation was that the HBV and HCV infection status before employment and the immune response to the initial HB vaccination series was not known. Moreover, the relation between the infection status and the NSIs was not investigated. Finally, for this study only hospital HCPs was investigated and health care providers in the primary health care centers and private clinics were not included, and this may influence the data collected for this group of personnel.