Students in medicine and other health professions are exposed to numerous occupational hazards, primarily biological hazards, during their academic careers at university. The aim of the present study was to investigate the seroprevalence characteristics of anti-HBsAg, anti-Measles, anti-Mumps, anti-Rubella and anti-Varicella IgG antibodies in healthcare students of a large teaching hospital in Rome.

To accomplish the study's aims, antibody serology data were gathered from students of Medicine and Surgery, Dentistry, and Health Professions at the Catholic University of the Sacred Heart (Rome Campus) during their first Health Surveillance visit, that took place from 2013 to 2023.

Our study sample included 2523 students, 44.4 % were protected against Hepatitis B, 87.3 % against measles, 85.5 % against mumps, 94.6 % rubella and 95.2 % against varicella. Differences in antibody coverage between age groups were statistically significant (p < 0.001), except for mumps. It found a lower probability of having seronegative anti-HBVs with an older date since the presumed primary vaccination.

In our sample, seropositivity rate against vaccine-preventable diseases, especially for Hepatitis B, was often inadequate to prevent possible biological risks connected with the activities carried out on the ward.

Currently, there are only a few studies on how immunocompromised cats, such as cats infected with feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV), respond to vaccination. Therefore, this study measured feline panleukopenia virus (FPV) antibodies in retrovirus-infected cats within a period of 28 days after FPV vaccination, and compared the immune response to that of non-infected cats.

Eight asymptomatic retrovirus-infected cats (four FeLV, four FIV), and non-infected age-matched control cats (n = 67) were vaccinated with a commercial FPV modified live virus (MLV). Pre- and post-vaccination antibody titres were measured by haemagglutination inhibition (HI) on days 0, 7 and 28. An HI titre ⩾1:40 was defined as protective. An adequate response to vaccination was defined as a four-fold titre increase or higher. Comparison of the immune response of retrovirus-infected and non-infected cats was performed.

Pre-vaccination FPV antibody titres ⩾1:40 were present in 100% (n = 8/8; 95% confidence interval [CI] 62.8-100) of retrovirus-infected and in 77.6% (n = 52/67; 95% CI 66.2-86.0) of non-infected cats. An adequate response to vaccination (titre increase ⩾four-fold) was seen in 1/8 retrovirus-infected cats (12.5%; 95% CI 0.1-49.2) compared with 22/67 non-infected cats (32.8%; 95% CI 22.8-44.8). In cats with high pre-vaccination titres (⩾1:160), a four-fold titre increase or higher was observed in 1/8 retrovirus infected cats (12.5%; 95% CI 0.1-49.2) compared with 4/42 non-infected cats (9.5%; 95% CI 3.2-22.6). None of the eight retrovirus-infected cats developed illness or vaccination side effects after vaccination with MLV against FPV within the 28 days. There were no significant differences between groups: for pre-vaccination titres; for at least four-fold titre increases following vaccination in either all cats or the cats with high pre-vaccination titres; and concerning adverse effects.

All retrovirus-infected asymptomatic cats had pre-vaccination FPV antibodies indicating protection against panleukopenia. Response of retrovirus-infected cats to vaccination was similar to the response of non-infected cats.

Objectives Recently, two point-of-care (PoC) feline immunodeficiency virus (FIV) antibody test kits (Witness and Anigen Rapid) were reported as being able to differentiate FIV-vaccinated from FIV-infected cats at a single time point, irrespective of the gap between testing and last vaccination (0-7 years). The aim of the current study was to investigate systematically anti-FIV antibody production over time in response to the recommended primary FIV vaccination series. Methods First, residual plasma from the original study was tested using a laboratory-based ELISA to determine whether negative results with PoC testing were due to reduced as opposed to absent antibodies to gp40. Second, a prospective study was performed using immunologically naive client-owned kittens and cats given a primary FIV vaccination series using a commercially available inactivated whole cell/inactivated whole virus vaccine (Fel-O-Vax FIV, three subcutaneous injections at 4 week intervals) and tested systematically (up to 11 times) over 6 months, using four commercially available PoC FIV antibody kits (SNAP FIV/FeLV Combo [detects antibodies to p15/p24], Witness FeLV/FIV [gp40], Anigen Rapid FIV/FeLV [p24/gp40] and VetScan FeLV/FIV Rapid [p24]). Results The laboratory-based ELISA showed cats from the original study vaccinated within the previous 0-15 months had detectable levels of antibodies to gp40, despite testing negative with two kits that use gp40 as a capture antigen (Witness and Anigen Rapid kits). The prospective study showed that antibody testing with SNAP Combo and VetScan Rapid was positive in all cats 2 weeks after the second primary FIV vaccination, and remained positive for the duration of the study (12/12 and 10/12 cats positive, respectively). Antibody testing with Witness and Anigen Rapid was also positive in a high proportion of cats 2 weeks after the second primary FIV vaccination (8/12 and 7/12, respectively), but antibody levels declined below the level of detection in most cats (10/12) by 1 month after the third (final) primary FIV vaccination. All cats tested negative using Witness and Anigen Rapid 6 months after the third primary FIV vaccination. Conclusions and relevance This study has shown that a primary course of FIV vaccination does not interfere with FIV antibody testing in cats using Witness and Anigen Rapid, provided primary vaccination has not occurred within the previous 6 months. Consequently, Witness and Anigen Rapid antibody test kits can be used reliably to determine FIV infection status at the time of annual booster FIV vaccination to help detect 'vaccine breakthroughs' and in cats that have not received a primary course of FIV vaccination within the preceding 6 months. The duration of antibody response following annual booster FIV vaccination and the resulting effect on antibody testing using PoC kits needs to be determined by further research. The mechanism(s) for the variation in FIV antibody test kit performance remains unclear.

Antibodies against hepatitis B surface antigen (HBsAg) wane over time following hepatitis B immunisation; hence, it is unclear whether people vaccinated in three-dose or four-dose schedules of the hepatitis B vaccine are still immune when the hepatitis B surface antibody (anti-HBs) level in their body is undetectable, or lower than the level usually considered protective. This question may potentially be answered indirectly by measuring the anamnestic immune response to a booster dose of vaccine. The term 'booster' (or revaccination) refers to an additional dose of hepatitis B vaccine (HBV) given some time post-primary vaccination to induce immune memory and improve protection against hepatitis B virus (HBV) infection.

To assess the benefits and harms of booster dose hepatitis B vaccination, more than five years after the primary vaccination, for preventing HBV infection in healthy individuals previously vaccinated with the hepatitis B vaccine, and with hepatitis B surface antibody (anti-HBs) levels below 10 mIU/mL.

We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Science Citation Index Expanded, conference databases, and reference lists of articles to January 2016. We also contacted authors of articles. In addition, we searched ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform for ongoing trials (May 2016).

Randomised clinical trials addressing anamnestic immune response to a booster dose of hepatitis B vaccine, more than five years after the primary vaccination, in apparently healthy participants, vaccinated in a three-dose or four-dose schedule of the hepatitis B vaccine during the primary vaccination, without receiving an additional dose or immunoglobulin.

Both review authors decided if the identified studies met the inclusion criteria or not. Primary outcomes included the proportion of participants with anamnestic immune response in non-protected participants and signs of HBV infection. Secondary outcomes were the proportion of participants that developed local and systemic adverse events following a booster dose injection. We planned to report the weighted proportion with 95% confidence intervals (CIs).

There were no eligible randomised clinical trials fulfilling the inclusion criteria of this review.

We were unable to include any randomised clinical trials on the topic; only randomised clinical trials will be able to provide an answer as to whether a booster dose vaccination is able to protect against hepatitis B infection.

To evaluate the immunological effects of three types of domestic 10-µg/dose hepatitis B vaccines in adults compared with a foreign vaccine, and to provide scientific evidence in support of adult hepatitis B vaccination.

Adults from five counties (Deqing, Changxing, Nanxun, Wuxing, Anji) in Huzhou City, Shaoxing County and Tongxiang County, Zhejiang Province, China were selected. Blood samples were taken to assess serum HBsAg, anti-HBs, and anti-HBc using a chemiluminescence immunoassay. Adults, aged 16 to 49 years and who were anti-HBs negative at baseline, received hepatitis B immunizations at 0, 1, and 6 months. Anti-HBs levels were assessed one month after the third and final vaccination.

A total of 1872 adults were immunized and the average positive rate was 89.5%. Four types of hepatitis B vaccine were used, including three from Chinese companies (Shenzhen Kangtai, Dalian High-Tech, and North China Pharmaceutical) and one from a UK company (GlaxoSmithKline). Their seroconversion rates were 81.67%, 95.05%, 89.64%, and 86.81%, respectively. There was a significant difference between the anti-HBs positive conversion rates of the four types (P<0.005) but the seroconversion rates among the different vaccines were not significantly different (χ(2)=2.123, P=0.145). The average anti-HBs geometric mean titers (GMTs) of non-immune adults immunized with each of the four vaccines were 177.28, 473.23, 246.13, and 332.20 mIU/ml, respectively. There were no statistically significant differences in the GMTs between the three types of domestic vaccine and the foreign vaccine (t=-1.575, P=0.116).

Domestic recombinant hepatitis B vaccines can achieve immunization effects comparable to those of a foreign vaccine.

Antibodies against hepatitis B surface antigen (HBs) wane over time after vaccination for hepatitis B (HB); hence, the duration of protection provided by the vaccine is still unknown but may be evaluated indirectly by measuring the anamnestic immune response to booster doses of vaccine.

To assess the benefits and harms of booster dose hepatitis B vaccination for preventing HB infection.

We searched The Cochrane Hepato-biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 4, 2010) in The Cochrane Library, MEDLINE, EMBASE, Science Citation Index Expanded, conference databases, and reference lists of articles to May 2010. We also contacted authors of articles and manufacturers.

Randomised clinical trials addressing anamnestic immune response to booster of HB vaccine five years or more after primary vaccination in apparently healthy participants, vaccinated in a 3-dose or 4-dose schedules of HB vaccine without receiving additional dose or immunoglobulin.

Two authors made the decisions if the identified publications on studies met the inclusion criteria or not. Primary outcome measures included the proportion with anamnestic immune response in non-protected participants and signs of hepatitis B virus infection. Secondary outcomes were the proportion with local and systemic adverse event events developed following booster dose injection. Weighted proportion were planned to be reported with 95% confidence intervals.

There were no eligible randomised clinical trials fulfilling the inclusion criteria of this review.

We were unable to identify randomised clinical trials on the topic. We need randomised clinical trials to formulate future booster policies for preventing hepatitis B infection.

A serosurvey targeting Hepatitis B virus (HBV)-vaccinated children born between 1986 and 1998 was conducted in 2001 in remote Taiwanese villages where a 1993 serosurvey indicated high vaccine failure. The HBV S antigen (HBsAg) seropositive rate among vaccinees of 3-6-year-old children in 2001 was significantly lower than that of 1993 and was higher among children who had a delayed vaccination schedule and received the plasma-derived vaccine. Vaccine escape variants were more prevalent among recipients of recombinant HBV vaccine residing in Hualien. Our study highlights the importance of continued monitoring of vaccinees for incidence of HBV infection in order to refine future vaccination policy.

One of the cardinal features of the immune response is immune memory: the size of the secondary antibody response to vaccination reflects the amount of immune memory that has been generated in an individual by the priming dose. We construct a mathematical model of the generation of immune memory and antibody in response to hepatitis B vaccines. The model predictions are compared to post-vaccination antibody titres from eight adult vaccine trials. The model demonstrates significant differences between different vaccines in both the time taken to generate immune memory and the amount of memory generated. The model provides theoretical support for the hypothesis that a single vaccine dose can generate protective immune memory.

Hepatitis B virus (HBV) causes acute and chronic liver diseases. Hepatitis B vaccination is recommended for health-care workers.

To assess the beneficial and harmful effects of hepatitis B vaccination in health-care workers.

We searched the trial registers of The Cochrane Hepato-Biliary Group, The Cochrane Library, MEDLINE, and EMBASE to February 2003.

Randomised trials comparing any dose, injection route, injection site, or schedule of hepatitis B plasma-derived vaccines (PDV) or recombinant vaccines (RV) versus placebo, no intervention, or another hepatitis B vaccine in health-care workers.

Two reviewers extracted the data independently. The reviewers assessed the methodological quality of the trials regarding generation of the allocation sequence, allocation concealment, double blinding, and follow-up. The results were presented as relative risk (RR) with 95% confidence intervals (CI).

We identified 21 randomised trials, all with one or more methodological weaknesses. Four trials demonstrated that PDV versus placebo significantly decreased hepatitis B events at maximum follow-up (RR 0.51, 95% CI 0.35 to 0.73). RV did not differ significantly from PDV in eliciting a protective hepatitis B surface antibody (anti-HBs) level in two trials. Both vaccines were well tolerated. Low-dose vaccine (1 or 2 microg) by the intradermal route resulted in significantly more participants without protective anti-HBs level compared with high-dose (10 or 20 microg) by the intramuscular route (RR 1.41, 95% CI 1.13 to 1.76). The intradermal route caused significantly more local adverse events, while the intramuscular route caused significantly more systemic adverse events. The gluteal injection produced significantly more participants without protective anti-HBs level than the deltoid injection. The prevalence of anti-HBs seroconversion by rapid vaccination (0, 1, and 2 months) was significantly lower than that by standard vaccination (0, 1, and 6 months). Booster vaccinations with different RV doses (2.5, 5, 10, 20, or 40 microg) produced similar prevalence of anti-HBs seroconversion in three trials assessing participants who did not respond to previous HBV vaccination.

PDV significantly prevents hepatitis B events. RV seems to be able to elicit similar protective anti-HBs levels. The intramuscular route with 20 microg RV was significantly more effective compared with the intradermal route with 2 microg RV as was the standard schedule compared with a rapid schedule and deltoid intramuscular injection compared with the gluteal intramuscular injection. It is unclear if booster vaccination of non-responders offers higher anti-HBs seroconversion and hepatitis B vaccine prevents the infection of hepatitis B mutants in health-care workers.

The long-term efficacy of hepatitis B vaccine, long-term effectiveness of hepatitis B immunisation programmes, immune memory induced by hepatitis B vaccine, current booster policies, and impact of hepatitis B virus mutants on immunisation programmes were reviewed at the Viral Hepatitis Prevention Board (VHPB) meeting in Sevilla, Spain, March 2004. The main focus was on universal vaccination programmes with data being presented from Italy, Saudi Arabia, Singapore, Spain, Taiwan, Thailand, The Gambia, and USA (Alaska).

To evaluate if HB vaccination can yield a booster effect on the anti-HBs level of those naturally acquired HBV positive markers.

Sera were collected from 1399 newly enrolled university students aged between 18-20 years at the entrance medical examination in 2001. Forty-four students (28 males and 16 females) with positive serum anti-HBs and anti-HBc markers served as an observation group and another 44 students (24 males and 20 females) without any HBV markers as the control. HB vaccination was given to all the students without positive serum HBsAg according to 0, 1, 6 month regimen and the peripheral venous blood was sampled from those of both observation and control groups for anti-HBs detection one month after the second and third doses. Anti-HBs levels were measured by ELISA.

The seroconversion rate of anti-HBs in the control group was 100% after the second dose, but the geometric mean titers (GMTs) were low. The tendency of serum anti-HBs changes after the 3rd dose was completely different between the two groups. Although more than half of those with positive anti-HBs and anti-HBc showed a mild increase of anti-HBs levels after the 2nd boosting dose (mean anti-HBs level was 320:198 mIU), but the increase of serum anti-HBs titer was much smaller than that in the control group. The averages of their initial serum anti-HBs levels and the levels after the 2nd and 3rd doses were 198, 320 and 275 mIU respectively. All the subjects from the control group had an obvious increase in their serum anti-HBs levels which was nearly 4 times the baseline level (302:78 mIU).

HB vaccination can not enhance anti-HBs levels in those with positive serum anti-HBs and anti-HBc markers.

To determine if the T cell memory to HBsAg can persist for a long time after hepatitis B (HB) vaccination.

Thirty one vaccine recipients who were healthcare workers (18 females and 13 males aged 34-58 years) from Utrecht University Hospital, Netherlands, and had previously received a standard course of vaccination for hepatitis B were investigated and another 9 unvaccinated healthy volunteers from the same hospital were used as the control. Blood samples were taken just before the experiment to test serum anti-HBs levels and the subjects were classified into different groups according to their serum titers of anti-HBs and vaccination history. Their peripheral blood mononuclear cells (PBMC) were isolated from freshly heparinized venous blood and the proliferative response of T lymphocytes to the recombinant hepatitis B surface antigen (HBsAg) was investigated.

Positive serum anti-HBs was found in 61.3% (19/31) vaccine recipients and a significant in vitro lymphocyte proliferative response to recombinant HBsAg was observed in all the vaccinees with positive anti-HBs. Serum anti-HBs level < or =10 IU/L was found in 38.7% (12/31) subjects. In this study, we specially focused on lymphocyte proliferative response to recombinant HBsAg in those vaccine recipients with serum anti-HBsAg less than 10 IU/L. Most of them had received a standard course of vaccination about 10 years before. T lymphocyte proliferative response was found positive in 7 of the 12 vaccine recipients. These results confirmed that HBsAg-specific memory T cells remained detectable in the circulation for a long time after vaccination, even when serum anti-HBs level had been undetectable.

The T cell memory to HBsAg can persist for at least 10 years after HB vaccination. Further booster injection is not necessary in healthy responders to HB vaccine.

The aim of the present study was to evaluate the long-term persistence of seroprotection after hepatitis B virus (HBV) vaccination. A total of 422 health care workers (HCWs) were evaluated 4.8-18.8 years after primary immunization (mean follow-up 11.8 years); 241 of them had received plasma-derived vaccines and 181 had been given yeast-derived vaccines; 107 subjects received a booster dose of yeast-derived vaccine 6 years after primary immunization with either plasma-derived or yeast-derived vaccines. Seroprotection was assumed when the anti-HBs titers were >10 mIU/ml. The overall response after primary immunization was 98.8%. Among subjects who reached a 10 year follow-up, those treated with plasma-derived vaccine had a seroprotection rate of 87.8 compared to 81.6% of those vaccinated with yeast-derived vaccines (P<0.001). Anti-HBs geometric mean titers (GMTs) after primary immunization were similar in the two groups, but were significantly lower at 10 years follow-up in the group that had received a yeast-derived vaccine (104 mIU/ml versus 244 mIU/ml in those who used a plasma-derived vaccine, P<0.05). Anti-HBs GMTs in the 107 subjects given the booster dose were 242 mIU/ml pre-booster titer, and rose to 35,171 mIU/ml after the booster dose. A mean 10.1 years after the booster dose, GMTs were 952 mIU/ml. Overall, the anti-HBs seroprotection rate was 95.4% (102 subjects). Based on GMT results, no booster dose is necessary in healthy adults for at least 10 years after primary immunization.

Of the 110 dentists who had presented seroconversion 50 days after the intradermal application of three 2 micrograms doses of the Belgian recombinant vaccine against hepatitis B (HB), administered eight years before at an interval of one month between the 1st and 2nd doses and of five months between the 2nd and 3rd doses, 51 were included for the assessment of the persistence of immunity. None of the dentists had hepatitis or had received HB vaccine during this period. All subjects were submitted to serological tests for the detection of the following markers of hepatitis B virus (HBV) infection: HBsAg, anti-HBc, HBeAg, anti-HBe, and anti-HBs, with no HBsAg, anti-HBc, HBeAg or anti-HBe being detected. A microparticle enzyme immunoassay (MEIA) revealed the presence of anti-HBs at protective titers (> or = 10 mIU/ml) in 42 dentists (82.4%), with the anti-HBs titer being higher than 100 mIU/ml in 36 of them (70.6%) (good responders), between 10 and 100 mIU/ml in 6 (11.8%) (poor responders), and lower than 10 mIU/ml in 9 (17.6%) (non-responders). According to clinical data and serological tests, none of the dentists had presented disease or latent HBV infection during the eight years following the first vaccination. A 2 micrograms booster dose was administered intradermally to eight dentists with anti-HBs titers lower than 10 mIU/ml (non-responders) and to six dentists with titers ranging from 10 to 100 mIU/ml (poor responders); the determination of anti-HBs one month later demonstrated the occurrence of seroconversion in the eight non-responders and an increase in anti-HBs titer in the six poor responders. In summary, the present results demonstrated the prolonged persistence of protection against HBV infection and the development of immunologic memory provided by vaccination against HB--with intradermal application of three 2 micrograms doses of the Belgian recombinant vaccine at 0, 1, and 6 months--carried out eight years before in 51 dentists.

Sixty healthy nonresponders were randomized to receive intramuscular (IM) high dose hepatitis B virus (HBV) vaccine versus IM standard dose HBV vaccine plus granulocyte-macrophage colony-stimulating factor (GM-CSF) at 0-2 months. Antibody to hepatitis B surface antigen was measured 1 month after each dose and 3 months after the last dose. Two regimens were equivalent in eliciting seroprotection in nonresponders. Weight-height index (WHI) <39 and alanine transaminase (ALT) <39 mg/dl predicted which nonresponders would seroconvert. A three-dose regimen of standard dose HBV vaccine plus GM-CSF may be a useful for seroprotection of healthy nonresponders.

Long-term protection against hepatitis B (HB) disease is dependent on persistence of a strong immune memory. This paper presents and discusses new knowledge that allows a better understanding of the mechanisms of long-term protection following hepatitis B vaccination. Studies have revealed links between specific lymphoproliferation, the in vivo humoral response and immune memory. The strength of immune memory and of a subsequent secondary immune response can therefore be predicted by the antibody response following primary vaccination. Vaccine antigen dose and structure have been identified as important influences in the primary antibody response and development of immune memory. The data and considerations presented support the use of highly immunogenic HB vaccines in order to provide long-lasting protection against HB disease.

We evaluated the response to the recombinant Hepatitis B vaccine using an accelerated schedule versus the traditional schedule by studying the immunologic memory induced in 200 children with HBs-Ag negative mothers. At seroconversion, the traditional schedule presented a higher percentage of children with serum HBs-Ag concentrations over 100 mIU/ml than the accelerated schedule. After five years this difference was no longer statistically significant and children who presented anti-HBsAg concentrations below 10 mUI/ml received an additional booster dose which stimulated the antibody concentration to exceed 100 mIU/ml in all cases. Recombinant HBV vaccine induced better long term immunologic memory when it was administered earlier.

Drug addicts represent the group of young adults with the lowest response to hepatitis B virus (HBV) vaccine. A study was carried out on 110 current intravenous heroin users attending the service providing assistance to intravenous drug users (IVDUs) (SERT) in Padua: 66.4% of them were found anti-hepatitis C virus (HCV)-positive and 33.6% were anti-HBc positive; 29.9% were positive for both. The subjects were vaccinated with 10 microg of yeast-derived vaccine at months 0, 1 and 2 (fast schedule). The overall response rate was 66.4%. Response seems to be affected by positivity to anti-HBc, but not to HCV infection.

The aim of this study was to evaluate the persistence of antibodies 7 years after hepatitis B booster administration in healthy adult volunteers who were vaccinated in 1986. In October 1986, 188 seronegative, healthy adult volunteers (117 men and 71 women) were vaccinated with a 20 micrograms dose recombinant DNA yeast-derived hepatitis B vaccine. Mean age of the study group was 23.3 years (+/- 0.28). Immunisation was carried out according to a 0-1-2 month vaccination schedule, with a booster dose at 12 months. Of the 159 subjects who received the full vaccination course, 63 (40%) had a blood sample taken 8 years after the first vaccination. Of these 63 subjects, five were excluded from the analysis due to an irregular vaccination schedule and four subjects did not complete the accompanying questionnaire on possible booster administration. So, 54 subjects remained available for further analysis. Fourteen individuals had received an additional booster of hepatitis B vaccine sometime between 1989 and 1994. The geometric mean titre (GMT) at month 13 for these 14 individuals was 1494 mIU ml-1, compared with 3103 mIU ml-1 for those who did not receive an interim booster. Forty subjects, who received no additional booster dose besides that of month 12, met the inclusion criteria of the follow-up study. Of these, all subjects except one were seropositive for anti-HBs at month 96 (GMT: 215.9 mIU ml-1). All subjects were still anti-HBc negative at that time. Distribution of individual antibody titres revealed that overall 92.5% of subjects retained protective antibody levels (> or = 10 mIU ml-1); 72.5% of vaccinees retained high levels of anti-HBs (> or = 100 mIU ml-1) as compared to 99.2 and 97.0% at month 13, respectively. A positive correlation was found between the subjects' titres at month 13 and month 96. A 0-1-2 dose vaccination course with a booster dose administered at month 12, induces a protective immune response which lasts at least until 7 years after the full vaccination course of the subjects. A positive correlation was found between the anti-HBs antibody titres at month 13 and month 96.

The efficacy of a 10 or 20 micrograms antigen load of HB recombinant vaccines is still being debated. A comparison of anti-HBs titres in two groups of healthy subjects vaccinated by the same schedule (0, 1 and 6 months) employing recombinant HB vaccines with different antigen loads, 20 micrograms (group A, 251 subjects) and 10 micrograms (group B, 256 subjects) was carried out. A seroprotection rate of 99.6 and 99.2% was observed for group A and group B, respectively, at the end of primary immunization. No statistically significant difference in seroprotection rate was observed. Group A showed significantly higher GMTs than group B for all age groups and for both sexes except for males above 25 years. The difference was more marked for younger age groups and for the female sex. These data support the higher immunogenicity of vaccine with 20 micrograms antigen load as compared to vaccines with 10 micrograms antigen load.

In a campaign to vaccinate health care workers, a three-dose schedule (0, 1, and 6 months) and a four-dose schedule (0, 1, 2, and 14 months) with hepatitis B (HB) vaccine were used. After primary immunization 26 subjects vaccinated with the 3-dose schedule and 4 subjects vaccinated with the 4-dose schedule had undetectable anti-HBs titres.

All these 30 non-responders received an extra dose of the same vaccine 2 months after primary immunization and a booster dose with a yeast-derived vaccine 6 years later. Anti-HBs levels were evaluated 1 month after the extra dose and after the booster dose.

One month after the extra dose 26.9% (7 of 26) of the subjects vaccinated with the 3-dose schedule became positive for anti-HBs. Six years later only two of these subjects had detectable anti-HBs. After the booster dose the seven subjects who responded to the extra dose showed an anamnestic type of response, and five additional subjects became positive for anti-HBs. Responders to the extra dose were significantly younger than the non-responders. In the four-dose group only one subject responded to the extra dose, and that subject maintained protective anti-HBs.

About 25% of non-responders to primary HB vaccination could benefit from an extra dose, and these subjects show an anamnestic type of response to HBs antigen even after 6 years. This response seems to be influenced by age.