Real-World Effectiveness of Mix-and-Match Vaccine Regimens against SARS-CoV-2 Delta Variant in Thailand: A Nationwide Test-Negative Matched Case-Control Study

The objective of this study is to explore the real-world effectiveness of various vaccine regimens to tackle the epidemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant in Thailand during September–December 2021. We applied a test-negative case control study, using nationwide records of people tested for SARS-CoV-2. Each case was matched with two controls with respect to age, detection date, and specimen collection site. A conditional logistic regression was performed. Results were presented in the form vaccine effectiveness (VE) and 95% confidence interval. A total of 1,460,458 observations were analyzed. Overall, the two-dose heterologous prime-boost, ChAdOx1 + BNT162b2 and CoronaVac + BNT162b2, manifested the largest protection level (79.9% (74.0–84.5%) and 74.7% (62.8–82.8%)) and remained stable over the whole study course. The three-dose schedules (CoronaVac + CoronaVac + ChAdOx1, and CoronaVac + CoronaVac + BNT162b2) expressed very high degree of VE estimate (above 80.0% at any time interval). Concerning severe infection, almost all regimens displayed very high VE estimate. For the two-dose schedules, heterologous prime-boost regimens seemed to have slightly better protection for severe infection relative to homologous regimens. Campaigns to expedite the rollout of third-dose booster shot should be carried out. Heterologous prime-boost regimens should be considered as an option to enhance protection for the entire population.

Rapid method through routine data to evaluate real-world vaccine effectiveness against coronavirus disease 2019 (COVID-19) infection: lessons from Thailand

The objective of this article is to draw lessons from the Thai experience in estimating vaccine effectiveness (VE) for coronavirus disease 2019 (COVID-19) based on routine service data. We found that a matched case–control design, using probability-based controls representing the varying vaccine coverage across the population over time, yielded a valid result for VE assessment. The proposed design has an advantage in its applicability drawing from the routine data monitoring system. Future studies that exercise other designs, such as test-negative and cohort studies, are recommended in order to compare and contrast the findings across different designs. To implement a continuous monitoring system on VE, the integration of data from different sources is needed. This requires long-term investment in the data monitoring system for the entire healthcare system.

Economic evaluation of rotavirus vaccination: an important step of the introduction to the national immunization program in Thailand

INTRODUCTION

World Health Organization recommends rotavirus vaccine for all national immunization programs (NIPs). To provide country-specific evidence, we conducted economic evaluation of a monovalent rotavirus vaccination using specific data of the pilot phase in Thailand.

METHOD

A Markov model was adopted to compare the 2020 birth cohort once receiving rotavirus vaccination versus no vaccination from healthcare and societal perspective over five years. Data on disease burden, vaccine effectiveness, costs, and utilities were taken from a cohort study in two provinces of Thailand.  Sensitivity analyses were performed to test the robustness of the results.

RESULTS

Rotavirus vaccination would reduce rotavirus diarrhea and costs of illness by 48% and 71%, respectively, over the first five years of life. At USD 13 per dose, vaccine was cost-effective with the ICERs of USD 4,114 and USD 1,571per QALY gained from healthcare and societal perspective, respectively. Results were sensitive to incidence and vaccine cost.  The budget for vaccine purchasing was estimated at USD13 million per year.

CONCLUSION

Incorporating rotavirus vaccination into the NIP substantially reduced health and cost outcomes and was cost-effective for both perspectives. However, the government needs to negotiate vaccine price prior to program implementation to achieve favorable budget impact.

Identification and characterization of a human G9P[23] rotavirus strain from a child with diarrhoea in Thailand: evidence for porcine-to-human interspecies transmission

An unusual rotavirus strain with the G9P[23] genotype (RVA/Human-wt/THA/KKL-117/2014/G9P[23]) was identified in a stool specimen from a 10-month-old child hospitalized with severe diarrhoea. In this study, we sequenced and characterized the complete genome of strain KKL-117. On full-genomic analysis, strain KKL-117 was found to have the following genotype constellation: G9-P[23]-I5-R1-C1-M1-A8-N1-T1-E1-H1. The non-G/P genotype constellation of this strain (I5-R1-C1-M1-A8-N1-T1-E1-H1) is commonly shared with rotavirus strains from pigs. Furthermore, phylogenetic analysis indicated that each of the 11 genes of strain KKL-117 appeared to be of porcine origin. Our observations provide important insights into the dynamic interactions between human and porcine rotavirus strains.

Evaluating the first introduction of rotavirus vaccine in Thailand: Moving from evidence to policy

BACKGROUND

We assessed the effectiveness and possible impact of introducing rotavirus vaccine into the routine immunization program.

METHODS

Two provinces were selected for an observational study, one where vaccine was introduced and another where vaccine was not available. In these areas, two sub-studies were linked. The prospective cohort study enrolled children 2month old and followed them to the age of 18months to detect all diarrhea episodes. The hospital surveillance study enrolled all children up to age 5 hospitalized with diarrhea whose fecal samples were tested for rotavirus. Rates of rotavirus hospitalizations in older children who had not been vaccinated in both settings provided data to determine whether immunization had an indirect herd effect. The key endpoints for the study were both vaccine effectiveness (VE) based upon hospitalized rotavirus diarrhea and herd protection.

FINDINGS

From the cohort study, the overall VE for hospitalized rotavirus diarrhea was 88% (95%CI 76-94). Data from hospital surveillance indicated that for 2 consecutive years, the seasonal peak of rotavirus admissions was no longer present in the vaccinated area. Herd protection was observed among older children born before the rotavirus vaccine program was introduced, who experienced a 40-69% reduction in admission for rotavirus.

CONCLUSIONS

Rotavirus vaccine was highly effective in preventing diarrheal hospitalizations and in conferring herd protection among older children who had not been vaccinated.

Full Genome Characterization of Novel DS-1-Like G8P[8] Rotavirus Strains that Have Emerged in Thailand: Reassortment of Bovine and Human Rotavirus Gene Segments in Emerging DS-1-Like Intergenogroup Reassortant Strains

The emergence and rapid spread of unusual DS-1-like intergenogroup reassortant rotavirus strains have been recently reported in Asia, Australia, and Europe. During rotavirus surveillance in Thailand in 2013-2014, novel DS-1-like intergenogroup reassortant strains having G8P[8] genotypes (i.e., strains KKL-17, PCB-79, PCB-84, PCB-85, PCB-103, SKT-107, SWL-12, NP-130, PCB-656, SKT-457, SSKT-269, and SSL-55) were identified in stool samples from hospitalized children with severe diarrhea. In this study, we determined and characterized the complete genomes of these 12 strains (seven strains, KKL-17, PCB-79, PCB-84, PCB-85, PCB-103, SKT-107, and SWL-12, found in 2013 (2013 strains), and five, NP-130, PCB-656, SKT-457, SSKT-269, and SSL-55, in 2014 (2014 strains)). On full genomic analysis, all 12 strains showed a unique genotype constellation comprising a mixture of genogroup 1 and 2 genes: G8-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. With the exception of the G genotype, the unique genotype constellation of the 12 strains (P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2) was found to be shared with DS-1-like intergenogroup reassortant strains. On phylogenetic analysis, six of the 11 genes of the 2013 strains (VP4, VP2, VP3, NSP1, NSP3, and NSP5) appeared to have originated from DS-1-like intergenogroup reassortant strains, while the remaining four (VP7, VP6, VP1, and NSP2) and one (NSP4) gene appeared to be of bovine and human origin, respectively. Thus, the 2013 strains appeared to be reassortant strains as to DS-1-like intergenogroup reassortant, bovine, bovine-like human, and/or human rotaviruses. On the other hand, five of the 11 genes of the 2014 strains (VP4, VP2, VP3, NSP1, and NSP3) appeared to have originated from DS-1-like intergenogroup reassortant strains, while three (VP7, VP1, and NSP2) and one (NSP4) were assumed to be of bovine and human origin, respectively. Notably, the remaining two genes, VP6 and NSP5, of the 2014 strains appeared to have originated from locally circulating DS-1-like G2P[4] human rotaviruses. Thus, the 2014 strains were assumed to be multiple reassortment strains as to DS-1-like intergenogroup reassortant, bovine, bovine-like human, human, and/or locally circulating DS-1-like G2P[4] human rotaviruses. Overall, the great genomic diversity among the DS-1-like intergenogroup reassortant strains seemed to have been generated through additional reassortment events involving animal and human strains. Moreover, all the 11 genes of three of the 2014 strains, NP-130, PCB-656, and SSL-55, were very closely related to those of Vietnamese DS-1-like G8P[8] strains that emerged in 2014-2015, indicating the derivation of these DS-1-like G8P[8] strains from a common ancestor. To our knowledge, this is the first report on full genome-based characterization of DS-1-like G8P[8] strains that have emerged in Thailand. Our observations will add to our growing understanding of the evolutionary patterns of emerging DS-1-like intergenogroup reassortant strains.

Predominant prevalence of human rotaviruses with the G1P[8] and G8P[8] genotypes with a short RNA profile in 2013 and 2014 in Sukhothai and Phetchaboon provinces, Thailand

Of 2,754 stool specimens collected from children with acute gastroenteritis during 2013-2014 in Sukhothai and Phetchaboon provinces, Thailand, 666 (24.2%) were positive for rotavirus A (RVA) in polyacrylamide gel electrophoresis (PAGE). The G and P types of all RVA-positive specimens were determined by semi-nested RT-PCR. G1P[8] (56.5%) was most prevalent, followed by G2P[4] (22.1%). Unusual G8P[8] human RVAs (HuRVAs) were detected at a high frequency (20.0%). Interestingly, 171 of the 376 G1P[8] HuRVAs and all of the 133 G8P[8] HuRVAs showed a short RNA pattern in PAGE. Thus, it was shown that the properties of HuRVAs have been markedly unusual in recent years in Thailand. J. Med. Virol. 89:615-620, 2017. © 2016 Wiley Periodicals, Inc.

Reassortment of Human and Animal Rotavirus Gene Segments in Emerging DS-1-Like G1P[8] Rotavirus Strains

The emergence and rapid spread of novel DS-1-like G1P[8] human rotaviruses in Japan were recently reported. More recently, such intergenogroup reassortant strains were identified in Thailand, implying the ongoing spread of unusual rotavirus strains in Asia. During rotavirus surveillance in Thailand, three DS-1-like intergenogroup reassortant strains having G3P[8] (RVA/Human-wt/THA/SKT-281/2013/G3P[8] and RVA/Human-wt/THA/SKT-289/2013/G3P[8]) and G2P[8] (RVA/Human-wt/THA/LS-04/2013/G2P[8]) genotypes were identified in fecal samples from hospitalized children with acute gastroenteritis. In this study, we sequenced and characterized the complete genomes of strains SKT-281, SKT-289, and LS-04. On whole genomic analysis, all three strains exhibited unique genotype constellations including both genogroup 1 and 2 genes: G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 for strains SKT-281 and SKT-289, and G2-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 for strain LS-04. Except for the G genotype, the unique genotype constellation of the three strains (P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2) is commonly shared with DS-1-like G1P[8] strains. On phylogenetic analysis, nine of the 11 genes of strains SKT-281 and SKT-289 (VP4, VP6, VP1-3, NSP1-3, and NSP5) appeared to have originated from DS-1-like G1P[8] strains, while the remaining VP7 and NSP4 genes appeared to be of equine and bovine origin, respectively. Thus, strains SKT-281 and SKT-289 appeared to be reassortant strains as to DS-1-like G1P[8], animal-derived human, and/or animal rotaviruses. On the other hand, seven of the 11 genes of strain LS-04 (VP7, VP6, VP1, VP3, and NSP3-5) appeared to have originated from locally circulating DS-1-like G2P[4] human rotaviruses, while three genes (VP4, VP2, and NSP1) were assumed to be derived from DS-1-like G1P[8] strains. Notably, the remaining NSP2 gene of strain LS-04 appeared to be of bovine origin. Thus, strain LS-04 was assumed to be a multiple reassortment strain as to DS-1-like G1P[8], locally circulating DS-1-like G2P[4], bovine-like human, and/or bovine rotaviruses. Overall, the great genomic diversity among the DS-1-like G1P[8] strains seemed to have been generated through reassortment involving human and animal strains. To our knowledge, this is the first report on whole genome-based characterization of DS-1-like intergenogroup reassortant strains having G3P[8] and G2P[8] genotypes that have emerged in Thailand. Our observations will provide important insights into the evolutionary dynamics of emerging DS-1-like G1P[8] strains and related reassortant ones.

Optimizing national immunization program supply chain management in Thailand: an economic analysis

OBJECTIVES

This study aimed to conduct an economic analysis of the transition of the conventional vaccine supply and logistics systems to the vendor managed inventory (VMI) system in Thailand.

STUDY DESIGN

Cost analysis of health care program.

METHODS

An ingredients based approach was used to design the survey and collect data for an economic analysis of the immunization supply and logistics systems covering procurement, storage and distribution of vaccines from the central level to the lowest level of vaccine administration facility. Costs were presented in 2010 US dollar.

RESULTS

The total cost of the vaccination program including cost of vaccine procured and logistics under the conventional system was US$0.60 per packed volume procured (cm(3)) and US$1.35 per dose procured compared to US$0.66 per packed volume procured (cm(3)) and US$1.43 per dose procured under the VMI system. However, the findings revealed that the transition to the VMI system and outsourcing of the supply chain system reduced the cost of immunization program at US$6.6 million per year because of reduction of un-opened vaccine wastage.

CONCLUSIONS

The findings demonstrated that the new supply chain system would result in efficiency improvement and potential savings to the immunization program compared to the conventional system.

Diphtheria outbreak in Thailand, 2012; seroprevalence of diphtheria antibodies among Thai adults and its implications for immunization programs

An age distribution shift in diphtheria cases during a 2012 outbreak in northeastern of Thailand suggests adults are increasingly at risk for infection in Thailand. Data regarding immunity against diphtheria among the adult Thai population is limited. We review a 2012 diphtheria outbreak in Thailand and conducted a nationwide seroepidemiological survey to determine the prevalence of diphtheria antibodies among Thai adults in order to inform immunization programs. A total of 41 confirmed cases, 6 probable cases and 101 carriers of diphtheria were reported from northeastern and upper southern Thailand. The diphtheria outbreak in northeastern Thailand occurred among adults aged > or =15 years; sporadic cases occurred among children from upper southern Thailand. We conducted a seroepidemiological survey of 890 Thai adults from 4 age groups (20-29, 30-39, 40-49 and 50-59 years) in 7 different geographical areas of Thailand (Chiang Mai, Ratchaburi, Chon Buri, Nakhon Si Thammarat, Phitsanulok, Khon Kaen and Songkhla). Diptheria toxin antibody levels were measured with a commercially available ELISA test. The seroprotection rate ranged from 83% to 99%, with the highest in eastern Thailand (Chon Buri, 99%) and the lowest in northern Thailand (Chiang Mai, 83%). Diphtheria antibodies declined with increasing age. We recommend one doseof diphtheria-tetanus toxoid (dT) vaccine once after 20 years of age in order to boost the antibody and revaccinations every 10 years to prevent future outbreaks.

Progress with rotavirus vaccines: summary of the Tenth International Rotavirus Symposium

Over 350 scientific, public and private sector experts from 47 countries convened at the Tenth International Rotavirus Symposium in Bangkok, Thailand on 19-21 September 2012 to discuss progress in the prevention and control of rotavirus, the leading cause of diarrhea hospitalizations and deaths among young children worldwide. Participants discussed data on the burden and epidemiology of rotavirus disease, results of trials of rotavirus vaccines, postmarketing data on vaccine impact and safety from countries that have implemented rotavirus vaccination programs, new insights in rotavirus pathogenesis, immunity and strain diversity, and key issues related to vaccine policy and introduction.

Molecular analysis of hepatitis B virus associated with vaccine failure in infants and mothers: a case-control study in Thailand

Perinatal transmission of hepatitis B virus (HBV) has been controlled incompletely despite adequate immunoprophylaxis in infants. The aim of this study was to characterize virological factors of HBV associated with vaccine failure in Thailand. Sera of 14 infected infants (13 HBeAg-positive and one HBeAg-negative) with vaccine failure and their respective mothers (group M1) were tested quantitatively for HBV DNA by real-time PCR, HBV genotypes and mutations were characterized by direct sequencing. Sera collected from 15 HBeAg-positive (group M2) and 15 HBeAg-negative (group M3) mothers whose infants had been vaccinated successfully served as controls. The results showed that group M1 and group M2 mothers had equal titers of HBV DNA but higher titers than group M3. All infected infants and their respective mothers had the same HBeAg status and HBV genotypes. DNA analysis in a pair of HBeAg-negative infant and mother revealed that both were infected with an HBV precore mutant (G1896A). Escape mutants in the "a" determinant region (residues 144 and 145) were detected in two (14%) infected infants. The prevalence of BCP mutations/deletions in groups M2 and M3 was higher significantly than in group M1 (P = 0.022 and P < 0.001, respectively). In conclusion, instead of the HBeAg status, a high titer of HBV DNA in mothers was the major contributor to perinatal transmission of HBV. Escape mutants might be associated with vaccine failure in some infants. BCP mutations/deletions in mothers might contribute to the prevention of mother-to-infant transmission of HBV.

Increased risk of developing chronic HBV infection in infants born to chronically HBV infected mothers as a result of delayed second dose of hepatitis B vaccination

This two-stage study (cross-sectional and case-control) assessed the effects of delayed second dose HB vaccination on the risk of developing chronic HBV infection in infants born to chronically HBV infected mothers. 521 infants enrolled received the first vaccination by the end of the day after birth, without HBIG. 15 of these infants were chronically HBV infected. In the case-control comparison, controlling for HBeAg in the mother, the risk of an infant becoming chronically infected was 3.74 times (95% CI=0.97-14.39) higher if the interval between the first and the second doses exceeded 10 weeks. This finding suggests it is important that immunization programs ensure timely second dose vaccination to infants born to mothers with chronic HBV infection. Nevertheless, due to the small sample size, these findings should be verified by larger studies.

Seroprevalence of antibodies to measles, mumps, and rubella among Thai population: evaluation of measles/MMR immunization programme

Stored serum specimens, from four regions of Thailand, of healthy children attending well baby clinics and of healthy people with acute illnesses visiting outpatient clinics were randomly sampled and tested for IgG antibody to measles, mumps, and rubella (MMR). The immunity patterns of rubella and mumps fitted well with the history of rubella and MMR vaccination, seroprotective rates being over 85% among those aged over seven years. A high proportion of younger children acquired the infection before the age of vaccination. MMR vaccination should preferably be given to children at an earlier age. For measles, 73% seroprotective rates among children, aged 8-14 years, who should have received two doses of measles/MMR vaccine, were lower than expected. This finding was consistent with the age-group reported in outbreaks of measles in Thailand. The apparent ineffectiveness (in relation to measles) of MMR immunization of 1st grade students warrants further studies.

Molecular epidemiological study of hepatitis B virus in Thailand based on the analysis of pre-S and S genes

AIMS

This study was undertaken to determine the prevalence and characteristics of hepatitis B virus (HBV) genotypes, antigen subtypes, "a" determinant variants and pre-S gene mutations circulating on a large scale in Thailand.

METHODS

The sequences of the Pre-S1, Pre-S2 and S regions were determined in serum samples of 147 HBsAg and HBV DNA-positive subjects who had been enrolled from the nationwide seroepidemiological survey conducted on 6213 individuals in 2004.

RESULTS

The results showed that genotypes C, B and A accounted for 87.1%, 11.6% and 1.3%, respectively. The distribution of the HBV antigen subtypes was: adr (84.4%), adw (14.2%) and ayw (1.4%). Regarding the "a" determinant, 2/43 (4.65%) and 2/104 (1.92%) samples of vaccinated and non-vaccinated subjects, respectively, displayed mutations, all ofwhich were Thr126Asn. Sequencing analysis showed the pre-S mutations in 14 (9.5%) samples, with pre-S2 deletion as the most common mutant (4.1%) followed by pre-S2 start codon mutation (2.9%), both pre-S2 deletion and start codon mutation (2.0%), and pre-S1 deletion (0.7%). The pre-S mutations were associated with older age and higher mean serum HBsAg level.

CONCLUSION

This study demonstrated that HBV genotype/subtype C/adr and B/adw were the predominant strains circulating in Thailand. The "a" determinant variants seemed to be uncommon, and might not be attributed to vaccine-induced mutation.

Seroprevalence of tetanus antibody in the Thai population: a national survey

Tetanus is a disease with high mortality and the most important measure for effective prevention is vaccination. Tetanus immunization has been introduced to Thailand's national immunization program for 30 years. Yet, the coverage and seroprevalence of tetanus antibody in vast parts of the population has not been assessed. This study has been performed on 1,277 subjects aged between 6 months and 60 years or above from four geographically distinct provinces of Thailand. Tetanus antibody levels were measured using a commercially available ELISA kit. Most of the Thai population had immunity against tetanus. The level of antibodies to tetanus, as demonstrated by the geometric mean titer of antibody (GMT) (and 95% confidence interval) was 2.62 (2.34-2.91) IU/ml. The highest and lowest GMT was found in subjects aged between 5 and 9 years, and above 60 years of age with GMT (and 95% confidence intervals) of 3.64 (3.34-3.96) and 1.24 (0.67-2.29) IU/ml respectively. The minimum protective level of antitoxin (>0.01 IU/ml) was detected in 99.7 % of subjects. More than 90% of subjects displayed durable antibody protection levels (DAPL) (> or = 1.0 IU/ml), except for subjects above the age of 60 years (82%). According to this study, the majority of the population expresses tetanus antibody levels that can confer long term protection. Yet, considering the lowest GMT and the highest incidence of tetanus cases found in subjects aged above 60 years, re-immunization should be targeted at this age group especially if they had sustained any tetanus-prone injury.

Seroepidemiology and genotypes of hepatitis C virus in Thailand

HCV can be classified into 6 major genotypes based on the phylogenetic analysis of the genomic sequences. The 3 major genotypes found in Thailand are 3, 1 and 6, respectively. In 2004, an epidemiological survey was carried out to evaluate the seroprevalence of HCV infections among populations aged 2-60 years in four provinces of Thailand, representing the North, Northeast, Center and South of the country, respectively. One hundred and twenty five out of 5,825 serum samples (2.15%) were positive for anti-HCV by ELISA. Fifty eight out of 100 anti-HCV positive samples (58.0%) were positive by RT-PCR of the 5'UTR. The core region of 45 representative samples was sequenced allowing classification into genotype variants 1a (6.7%), 1b (26.7%), 2a (2.2%), 2c (2.2%), 3a (51.1%), 3b (2.2%) and 6 (8.9%). This information might be crucial for public health surveillance and prevention of HCV infection.

Declining trend in the seroprevalence of infection with hepatitis A virus in Thailand

Since the mid 1970s, infection with hepatitis A virus (HAV) in Thailand has shifted from hyper-endemic to mesoendemic. In 2004, to explore this trend in prevalence further, 3997 subjects from four geographically distinct provinces of Thailand were tested, in a commercial ELISA, for antibodies to HAV. The results indicate that the seroprevalence of HAV continues to fall, almost certainly because the profound socio-economic development that has occurred over the last few decades in Thailand has brought with it significant improvements in sanitation and personal hygiene. As exposure to HAV declines, however, the risks of symptomatic and potentially severe infection in adulthood (rather than asymptomatic infection during childhood) and of epidemics of such infection, which would lead to profound economic loss, increases. Improvements in hygiene and sanitation to reduce exposure to the virus and measures to reduce the incidence of symptomatic disease in those infected, such as vaccination (which may only be cost-effective when targeted at high-risk groups), need to be carefully considered.

Who gets hospitalized for influenza pneumonia in Thailand? Implications for vaccine policy

Risk factor information for severe complications of interpandemic influenza is needed to inform vaccine policy in Thailand. We identified patients with lab-confirmed influenza who were hospitalized with pneumonia during September 2003 to August 2004. Among the 80 case-patients identified through a population-based pneumonia surveillance system in eastern Thailand, cases were 6.2 and 11.1 times more likely to be among persons<1 year old and >75 years old, respectively, compared with the overall population. Cases were also 7.6 times more likely to have chronic respiratory disease. In Thailand, the young, elderly, and those with chronic disease were at high risk for hospitalized pneumonia from influenza.

Hepatitis B seroprevalence in Thailand: 12 years after hepatitis B vaccine integration into the national expanded programme on immunization

OBJECTIVES

To evaluate the impact of the universal hepatitis B (HB) vaccination programme on the prevalence of hepatitis B surface antigen (HBsAg) carriers and immunity to HB virus infection among children <18 years and to determine the HB seroprevalence in the Thai population.

METHODS

We enrolled people in four provinces, including Chiangrai, Udon Thani, Chonburi and Nakhon Si Thammarat to geographically represent populations in the North, Northeast, Center and South of the country respectively. Serology for HBsAg, anti-hepatitis B surface (anti-HBs), and anti-hepatitis B core (anti-HBc) was tested using ELISA commercial kits. In total, 6213 subjects aged 6 months to 60 years from the four provincial hospitals and two to three district hospitals of each participating province participated.

RESULTS

Overall HBsAg, anti-HBs, and anti-HBc seropositive rates amounted to 4%, 41.6% and 26.5% respectively. Of 2887 participants aged 6 months to 18 years, 2303 were born after (group I) and 584 prior to (group II) HB vaccine integration into the expanded programme on immunization of each participating province. The HBsAg seropositive rate was 0.7% among group I children and 4.3% among group II children. The prevalence rate of anti-HBc was 2.9% in group I and 15.8% in group II. In children under 18 years, the HBsAg carrier rate was 0.98% among complete vaccinees and 1.36% among participants without vaccination.

CONCLUSIONS

This finding supports the efficacy of universal HB immunization in reducing the prevalence of HB infection in Thailand which is a highly endemic country.

Exposure to heat and freezing in the vaccine cold chain in Thailand

This study investigated exposure to heat and freezing of vaccines used in Thailand's National Immunization Program. Cold chain temperatures on 48 randomly selected shipment routes nationwide were monitored. Measles and hepatitis B vaccines were despatched with recording devices and subsequently tested. The study found that extremes of cold appear to be the more significant problem. Heat exposure was relatively brief and not at very high temperatures, so vaccine deterioration was unlikely, as was confirmed by measles vaccine testing. Exposure to temperatures below -0.5 degrees C was widespread, which would be expected to damage hepatitis B vaccine, but shake tests did not detect damage.

Evaluation of growth monitoring and promotion (GMP) surveillance system Thailand 2002

This study aims to describe the current practice on growth monitoring and promotion (GMP) system in Thailand, identify its constraints and recommend appropriate solutions. In the four provinces studied, 80 health centres were systematically selected. A total of 80 health officers, 183 health volunteers and 1,200 caretakers were interviewed and tested for GMP knowledge and practices. One-fourth of the health officers and half of the volunteers did not understand the objectives of the GMP. More than half of the health officers and volunteers did not have the skill to weigh properly. About half of the volunteers could not plot and explain the growth chart correctly. Only 40% of the caretakers understand the growth chart. Documentation of weight on child health card is lacking. We recommend adequate trainings and supervisions for health officers and volunteers, revised GMP guidelines to enhance integration with other programmes, and a study to identify the effectiveness of the GMP.

Leptospirosis: skin wounds and control strategies, Thailand, 1999

After an outbreak of leptospirosis in workers who participated in cleaning a pond during September 1999 in Thailand, a serologic survey was conducted. Among a cohort of 104 persons from one village who participated in pond cleaning activity, 43 (41.3%) were seropositive for immunoglobulin M antibodies against Leptospira, indicating recent infection. Only 17 (39.5%) of 43 seropositive persons reported a recent febrile illness; the remaining seropositive persons were considered asymptomatic, suggesting that asymptomatic leptospirosis infection may be common where leptospirosis is endemic. Multivariable logistic regression indicated that wearing long pants or skirts was independently protective against leptospirosis infection (OR(adjusted) = 0.217), while the presence of more than two wounds on the body was independently associated with infection (OR(adjusted) = 3.97). Educational efforts should be enhanced in areas where leptospirosis is endemic to encourage the use of protective clothing. In addition, wound management and avoidance of potentially contaminated water when skin wounds are present should be included in health education programs.

Diphtheria in Thailand in the 1990s

Diphtheria remains endemic in developing countries, but there are limited published data on the subject. Thailand's diphtheria surveillance data are relatively complete and may give a fuller picture of the situation in similar countries. After routine immunization began in 1977, the incidence of reported diphtheria decreased by >98% to <0.1 case per 100,000 persons annually in the 1990s. Despite infant immunization coverage of >90%, diphtheria cases were reported throughout the 1990s, primarily among children <15 years old. Outbreaks were linked to both persistent endemic circulation and to importation of toxigenic Corynebacterium diphtheriae; suboptimal immunization coverage in minority and disadvantaged groups contributed. A serologic survey found 25% of adults 20-39 years old and 14% of adolescents 10-19 years old lacked immunity to diphtheria; these data indicate an accumulation of susceptible adolescents and adults. Diphtheria remains a threat in Thailand; improvements in diphtheria control will depend on improving childhood immunization coverage in Thailand and the surrounding region.

Food poisoning outbreak from contaminated fish-balls

On February 9th, 1998, a food poisoning outbreak occurred at a boarding school for underprivileged students. An unmatched case-control study was done. An environmental survey, laboratory study of rectal swab culture, fish-balls, water and the cooking utensils were also performed. There were 132 suspect cases, of which the attack rate in teachers was 9.8 per cent (4/41), 16.7 per cent (1/6) in the food handlers and 15.7 per cent (127/810) in the students. The median incubation period was 18 hours. Analysis of food consumption revealed those who ate lunch noodles had the highest risk (OR 3.8, 95% CI 0.6-5.9). In details of food components, those who ate fish-balls in curry had the only significant risk (OR 3.5, 95% CI 1.2-0.8) of becoming ill when compared to those who did not. Fish-balls in noodles and curry had a dose response relationship. Bacterial culture from 25 grams of fish-balls was positive for Vibrio parahaemolyticus. The fish-balls in noodles and curry were identified as the implicated food. The modes of contamination were uncooked food, cooking utensils and the food handlers. The manufacturer, which had no license to operate and had poor standards of sanitation, was closed by the Food and Drug Administration.

An outbreak of Influenza A virus in a hilltribe village of Mae Hong Son Province Thailand, 1997

An outbreak of Influenza A virus occurred in a hilltribe village between July 18th and August 8th, 1997. The overall infection rate was 92.5 per cent. The household infection rate was higher in the crowded part of the village. The symptoms analyzed after all, were fever (100%), cough (99%), headache, myalgia (78.1%) and rhinorrhea (50.5%). The patients were self - recovery within 5-7 days. Isolation and Haemagglutination inhibition test (HI) were undertaken to identify the causative agent. The results were positive for influenza A/Wuhan/359/95(H3N2) - like strain. The outbreak did not spread to the town, possibly because of the differences in environmental condition. Predisposing factors of the village that may have influenced the outbreak were crowded living quarters, cold (8 - 10 degrees C) and moist weather, poor personal hygiene and improper sanitation.

Screening assessment of persons 40-59 years of age in rural Thailand by a mobile health unit

This paper reports a screening survey using a mobile unit to determine the prevalence of chronic disorders among persons aged 40-59 years in rural Thailand. A total of 4,812 persons from all the 54 rural villages in Mae Sot District, Tak Province, northern Thailand, were interviewed and examined in 1995. A higher proportion (59.3%) of men were current tobacco smokers than among women (40.4%). A higher proportion (69.6%) of men were current alcohol drinkers compared with women (38.6%). Cutting/piercing was the most frequently reported injury, followed by falls. About half (47.9%) of the persons surveyed had a body mass index (BMI) between 20 and 24.9 and only 2.6 per cent had a BMI of 30 or over. The overall prevalence rates of hypertension and diabetes in the persons surveyed were 13.3 per cent and 2.4 per cent respectively. Of the persons screened, 28.8 per cent had borderline-high blood cholesterol (200-239 mg/dl) and 12.9 per cent had high blood cholesterol (> or = 240 mg/dl). About 61 per cent of hypertensive persons, 92 per cent of diabetic persons, and nearly all of those with dyslipidaemia were first detected during this screening programme. Five women with breast cancer and 22 with benign breast disorders were also identified during the survey. A screening programme using a mobile unit may be useful in identifying treatable disorders in rural areas, where existing screening services cannot effectively cover the population at risk.

Recurrence of yaws outbreak in Thailand, 1990

In November 1990, an outbreak of yaws was reported in a rural village of southern Thailand. A survey consisting of history taking, physical examination and blood tests for VDRL and TPHA was undertaken in the whole village and in the primary school of the village. A yaws case was defined as a person who had a positive VDRL confirmed by TPHA without history of other treponemal infection or post-treatment of yaws. Fifty-four cases, an attack rate of 23%, were found in the age range from 2 to 79 years old. The epidemic curve started with a few cases in 1989 and early 1990 with an increasing number of cases from June, and reached its peak in November. Half of the cases (53.7%) were children under 15 years. Male cases were higher than female (1.5:1). A survey of 105 primary school students found an attack rate of 32% (34/105) and the prevalence was higher in younger classes. Benzathine penicillin injection was given to cases for treatment. From this investigation, the Ministry of Public Health was alerted about the recurrence of yaws. Strengthening health education and surveillance activities was recommended in adjacent districts and provinces. The extent of the problem was assessed through surveys among school children and expanded to their family members if cases of yaws were found.