Abstract
Vaccination is the appropriate measure to protect military personnel against the hepatitis B virus (HBV) infection. Testing the military personnel for anti-HBs levels after vaccination is vital in re-vaccinating those that have not developed protective immunity. The aim of the current study was to determine the immunity in a group of vaccinated Sri Lankan military personnel (n = 150; age = 26–44 years) following a complete course of hepatitis B virus surface antigen (HBsAg) vaccination by assessing the antibodies against HBsAg (anti-HBs) levels. Three months after the last dose of the vaccination, blood samples were collected from the study population and tested for anti-HBs levels using a commercially available ELISA. Of the 150 military service men tested, 139 (92.67%) had anti-HBs levels higher than 10 mIU/mL, WHO approved levels for protective immunity against HBV infection. Of the 139 that had sufficient anti-HBs levels, 24% (36/150) had anti-HBs levels between 10 and 100 mIU/mL and 68.67% (103/150) had anti-HBs levels > 100 mIU/mL. Overall, 7.33% (11/150) participants had anti-HBs levels < 10 mIU/mL. Sero-conversion to > 10 mIU/mL anti-HBs was more than 90% in those that were less than 40 years of age and it was less than 90% in those that were more than 40 years of age.
Keywords: Hepatitis B virus, HBsAg immunization, Protective immunity, Sri Lanka
Hepatitis B Virus (HBV) infection is a major global health concern and can cause severe infection in non-immune adults. There are around 400 million chronic carriers worldwide and around 650,000 deaths are being notified annually due to complications caused by either acute or chronic HBV infection [12]. Around 75% of these deaths are known to occur in Southeast Asia and Africa [10]. The prevalence of hepatitis B surface antigen (HBsAg) carriage varies by the geographic area and it is estimated that more than one third of the world’s population has been infected with HBV at some point in life [1].
Universal immunization against HBV is considered to be the best way of preventing HBV infection [5]. HBV vaccination is able to stimulate a long-term immune response in more than 90% healthy immuno-competent individuals after a complete course of vaccination [16]. This percentage of vaccination efficacy in healthy individuals can prevent between 537,000 and 660,000 HBV related deaths annually [7]. Sri Lanka recommends a standard 0, 1 and 6 month schedule with any WHO approved recombinant DNA vaccine (http://www.epid.gov.lk/web/images/stories/Immunization_Guide_2012.pdf).
The criterion for immunity and its assessment of appropriate concentration of anti-HBs in the serum remains mandatory for adult vaccinees [6]. High levels of antibody production would lead to a long lasting protective immunity. The duration of protection depends on the levels of anti-HBs in the serum and anti-HBs levels > 10 mIU/mL indicates protective immunity [6]. On contrary, individuals who develop anti-HBs levels < 10 mIU/mL after three doses of vaccination are considered “non-immune” [8]. A non-response to the HBV vaccination might be due to many factors, such as improper vaccine storage, drug abuse, smoking, infections, age of the individual, genetics and obesity [18].
Immunisation of risk groups such as health care and military personnel is mandatory. The exact incidence or prevalence of HBV in the general population of Sri Lanka is unknown [13]. In 2003 in Sri Lanka made HBV vaccination as part of the country’s national immunization programme for childhood immunization [4]. However, in adult vaccinees, the response to HBV vaccination is not routinely tested in the healthcare and military settings. Thus, the objective of the current study was to determine the immunity by assessing the anti-HBs levels in a group of vaccinated Sri Lankan military personnel against HBV infection.
Ethical approval for this study was obtained from the Ethical Review Committee, Faculty of Medicine, General Sir John Kotelawela Defence University of Sri Lanka. For the study, 150 Sri Lankan military service men within 26–44 years of age were selected as a convenient sample. All service men were given three doses of the HBV vaccine (GeneVac-B, India). Three months after completing the final dose of the vaccination, the study group was bled to collect blood samples for testing the anti-HBs levels. Serum were separated and subjected to a quantitative ELISA (Fortress Diagnostics, United Kingdom). Manufacturer instructions were followed and the OD values were recorded. The OD values were converted to Log values to construct a standard curve for anti-HBs levels in order to interpret the results.
Of the 150 service men tested following a complete course of HBV vaccination, 92.67% (139/150) participants developed anti-HBs levels > 10 mIU/mL. Of these, 24% (36/150) service men had anti-HBs levels between 10 and 100 mIU/mL and 68.67% (103/150) service men had anti-HBs levels > 100 mIU/mL. However, 7.33% (11/150) service men had anti-HBs levels < 10 mIU/mL (Table 1). Sero-conversion to > 10 mIU/mL anti-HBs rate was > 90% in those that were less than 40 years of age and it was < 90% in those that were more than 40 years of age (Table 1).
Table 1.
Anti-HBs levels following a single course of HBV vaccination in the study population under different age groups and immune status of the study population (n = 150)
| Age (years) | < 10 mIU/mL Non-immune |
10–100 mIU/mL Immune |
> 100 mIU/mL Immune |
|||
|---|---|---|---|---|---|---|
| n | % | n | % | n | % | |
| 26–30 | 2 | 6.25 | 8 | 25.00 | 22 | 68.75 |
| 31–35 | 4 | 6.89 | 14 | 24.15 | 40 | 68.96 |
| 36–40 | 3 | 7.15 | 10 | 23.80 | 29 | 69.05 |
| 41–44 | 2 | 11.11 | 4 | 22.22 | 12 | 66.67 |
| Total | 11 | 7.33 | 36 | 24.5 | 103 | 68.67 |
| Age (years) | Sero-conversion rate > 10mIU/mL in percentage (%) |
|---|---|
| 26–40 | 93.19 |
| 41–44 | 88.89 |
The results of the study are in agreement with global and national findings where sero-conversion rates range between 90 and 95%, while non-immune individuals lie between 5 and 10% following a complete course of HBsAg vaccination. Based on a Sri Lankan study [4], 9.9% of the vaccinated health care workers did not develop sufficient anti-HBs levels; 23.7% had anti HBs titres between 10 and 100 mIU/mL and the rest (66.4%) had an anti-HBs titre > 100 mIU/mL. In a more recent study conducted among the HBsAg vaccinated Allied Health Science students (n = 89) of the University of Peradeniya, > 98% of the vaccinees had protective immunity of > 10 mIU/mL anti-HBs following a complete course of vaccination [3]. Taken together the findings of the current and previous studies, it is necessary to test for anti-HBs levels following a complete course of vaccination as 5–10% of the adults might not develop protective immunity following a complete course of HBsAg vaccination. This will help to identify risk groups to re-vaccinate to optimize the vaccination efficacy in those that have a risk of exposure such as military service men and health care workers.
Based on an Indian study [9], 32.4% of those with protective immunity were low responders (anti-HBs level between 10 and 99 mIU/mL) and 52.9% were high responders (anti-HBs > 100 mIU/mL). According to a Sri Lankan study [14], 9.5% of the study participants had anti-HBs levels < 10 mIU/mL and the majority (54%) showed an antibody response > 100 mIU/mL following a complete HBV vaccination. In a different Sri Lankan study [15], of the 152 nursing staff tsted, 7.7% did not develop protective immune immunity following a complete HBV vaccination. In the current study, there were 24% low responders and 68.67% high responders when tested for anti-HBs levels 3 months after a complete course of vaccination.
A significant association was noted between age at vaccination and the immune response in the current study. When the age at vaccination was higher than 40 years, the rate of sero-conversion to anti-HBs was less than 90%, when the age at vaccination was less than 40 years, the rate of sero-conversion to anti-HBs was higher than 90% (p < 0.05) as tested by the Chi square test. Similar findings have been reported by previous studies too [3, 4, 17].
Gender, age, smoking and obesity are a few factors influencing the development of protective immune response. McMahon et al. [11] reported males had higher antibody level than females. According to Abdul et al. [2] in Bangladesh, only 85.88% of the vaccinated males had protective level of anti-HBs whereas 92.31% of the vaccinated females had protective level of anti-HBs. However, we cannot comment on the gender differences in responding to HBsAg immunization as the current study sample did not have females.
Based on the findings of the current study, following a complete course of HBV vaccination, 92.67% (139/150) vaccinees had anti-HBs titre higher than 10 mIU/mL and thus had protective immunity against HBV infection; 7.33% (11/150) vaccinees had < 10 mIU/mL of anti-HBs levels and were non-immune. Military service men with < 10 mIU/mL of anti-HBs levels should go for another complete course of vaccination and test for anti-HBs levels.
Funding
This study was supported by Postgraduate Institute of Science, University of Peradeniya, Sri Lanka.
Footnotes
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