Punnee Pitisuttitham

Simultaneous administration of oral rhesus-human reassortant tetravalent (RRV-TV) rotavirus vaccine and oral poliovirus vaccine (OPV) in Thai infants

Rhesus-human reassortant tetravalent (RRV-TV) oral rotavirus vaccine was given at the same time as oral poliovirus vaccine (OPV) or inactivated parenteral poliovirus vaccine (IPV) to Thai infants at 2, 4 and 6 months of age. Sera for rotavirus antibody studies were taken prior to and one month after each vaccination. After the first dose of vaccine at 2 months of age, 37% of the infants receiving rotavirus vaccine with IPV but only 10% of those receiving it with OPV showed a seroconversion by rotavirus IgA ELISA antibody test (p < 0.001). Likewise, neutralizing antibody seroconversion rates in initially seronegative subjects to rhesus rotavirus type 3 (RRV-3) after the first dose of RRV-TV vaccine were higher if the vaccine was given with IPV (74%) than if given with OPV (39%) (p = 0.0069). After the second and third doses of vaccine, the rotavirus IgA ELISA and RRV-3-neutralizing antibody response rates were not different between groups. Development of neutralizing antibodies to human rotavirus serotypes 1, 2 and 4 in the first seven months of life in vaccinees receiving rotavirus vaccine with OPV tended to occur at a lower rate than in those receiving rotavirus vaccine with IPV but the antibody levels were not significantly different at 7 months of age. Poliovirus type 2 and type 3 antibody responses were not different in infants receiving the rotavirus vaccine with OPV as compared with infants receiving only OPV. The mean poliovirus type 1 antibody level was slightly but not significantly lower at 5 and 7 months of age in infants that received both rotavirus vaccine and OPV.(ABSTRACT TRUNCATED AT 250 WORDS)

Seroprevalence of varicella-zoster virus antibody in Thailand

Abstract Objective: To determine the seroprevalence of varicella-zoster virus antibodies in a wide age range of healthy subjects in Thailand. Design and Methods: In 1994, blood samples were collected from 559 volunteers aged 4 months to 77 years from the Bangkok area; questionnaires about socioeconomic background and history of chickenpox or herpes zoster were also completed. Serum samples were assayed for specific varicella-zoster virus (VZV) IgG antibodies using a commercial enzyme-linked immunosorbent assay kit. Results: The seroprevalence rate (61.4% overall) increased with age: less than 1 year, 10.2%; 1 to 4 years, 24.1 %; 5 to 9 years, 62.5%; 10 to 14 years, 70.4%; 15 to 19 years, 78.9%; 20 to 29 years, 69.2%; 30 to 39 years, 96.1 %; 40 to 49 years, 100%; and 50 years and older, 98.0%. No significant differences in the VZV antibody prevalence with respect to gender, family size, or family income were seen. There was good correlation between varicella history and seropositivity: 92.9% of subjects with a varicella history were seropositive. Conclusions: In this urban population, approximately one in three adolescents and young adults lacked natural immunity against varicella. The results suggest that vaccination programs in Thailand and probably other tropical countries should include susceptible adolescents and adults who are at high risk of developing severe varicella and resultant complications.

Vaccination of Thai infants with rhesus-human reassortant tetravalent oral rotavirus vaccine

In a randomized double blind placebo-controlled study, the rhesus-human reassortant tetravalent oral rotavirus vaccine (dose 4 x 10(4) plaque-forming units) was evaluated in Thai infants immunized at ages 2, 4 and 6 months. To investigate dose responses and to compare vaccine-induced and naturally acquired rotavirus immunity in the study population blood specimens were collected before and 1 month after each vaccination and at 12 months of age. No adverse reactions attributable to the vaccine were detected in the vaccinees. Sixty-three of 94 (67%) vaccine recipients showed a seroconversion in rotavirus IgA enzyme-linked immunosorbent assay antibodies after one or more doses, whereas only 15 of 93 (16%) placebo-vaccinated control children showed an IgA enzyme-linked immunosorbent assay antibody response, suggestive of natural rotavirus infection, between 2 and 7 months of age. By measuring rhesus rotavirus-neutralizing antibodies a seroconversion was detected in 49% of the vaccinees and 14% of the controls between 2 and 7 months of age. The geometric mean titers of neutralizing antibodies to human rotavirus serotypes 1, 2, 3 and 4 after the completion of vaccinations and at 12 months of age were higher in the vaccinees than in the controls. It is concluded that, even though maternally acquired rotavirus antibodies are commonly present, the rhesus-human reassortant tetravalent vaccine is immunogenic in many Thai infants ages 2 to 6 months. The immunogenicity of this vaccine is enhanced by multiple doses.

Measles vaccination of Thai infants by intranasal and subcutaneous routes : possible interference from respiratory infections

Reactogenicity and seroresponses were studied after standard doses of Edmonston-Zagreb measles vaccine were given intranasally (i.n.) and subcutaneously (s.c.) to 6-month-old Thai children. Few children given i.n. vaccine (2/31), but most (13/21) given s.c. vaccine, seroconverted. All but 1 of 51 children were seropositive after receiving vaccine s.c. at 9 months-of-age. Upper respiratory infection (URI) outbreaks with onsets in the week following vaccination occurred after each vaccination session and were equally common in all groups. URIs following i.n. vaccination at 6 months may have adversely affected response to i.n. vaccine, while URIs after s.c. vaccination at 9 months adversely affected final geometric mean antibody titers. I.n. measles vaccination does not appear to be an acceptable route for routine vaccination.

Comparison of Enhanced Potency Inactivated Poliovirus Vaccine (EIPV) Versus Standard Oral Poliovirus Vaccine (OPV) in Thai Infants

Enhanced potency inactivated poliovirus vaccine (EIPV), combined with diphtheria-tetanus-pertussis (DTP) vaccine, was compared with oral poliovirus vaccine (OPV) regarding immunogenicity in Thai infants, vaccinated at 2, 4 and 6 months of age. EIPV induced significantly higher seroconversion rates than OPV to all 3 poliovirus types after the second and third immunization. After 3 doses of each vaccine, at 7 months of age, all infants receiving EIPV proved seropositive for poliovirus type 1, type 2 and type 3 neutralizing antibodies, whereas of those receiving OPV, 9% remained seronegative (titre < 1:4) for type 1 (p = 0.0042) and 11% for type 3 (p = 0.0013). All participating children were given an additional dose of OPV at the age of 9 months and tested again at 12 months of age. At that point, virtually all infants had poliovirus neutralizing antibodies, but the geometric mean titres to each poliovirus type were significantly higher in the vaccinees who had received EIPV. It is concluded that the greater immunogenicity of EIPV vis-à-vis 3 doses of OPV may be biologically significant for protection against poliovirus types 1 and 3 in countries where cases of poliomyelitis occur in young children. These findings warrant considering EIPV, alone or in combination with OPV, for an immunization programme in Thailand and similar countries in the future.

Adverse impact of infections on antibody responses to measles vaccination.

Antibody titres were determined in 102 Thai infants who were vaccinated at 9-months of age during the respiratory disease season. The symptom densities of illnesses at or following vaccination, including rhinorrhea and diarrhea, were significantly lower among seroconverters, although the simple presence or absence of specific symptoms was not significantly related to seroconversions. Logistic regression indicated that neutralization test antibody titres below the median titre of 1:80 following vaccination were significantly more frequent among those with rhinorrhea when vaccinated and among those with diarrhea after vaccination. Compared with a referent group without these symptoms, titres were lower in those who had rhinorrhea when vaccinated, rhinorrhea during the first week post vaccination, and diarrhea in either of the two follow-up weeks. Illnesses concurrent or subsequent to measles vaccination adversely affected antibody responses in these study objects.

Clinical and bacteriological studies of El Tor cholera after ingestion of known inocula in Thai volunteers

Twenty-six healthy adult Thai volunteers were recruited for clinical and bacteriological studies of cholera induced by oral inoculation with Vibrio cholerae El Tor Inaba strain N16961. Vibrio dosages of 0.3 x 10(4), 1.6 x 10(5) and 1.9 x 10(6) c.f.u. were given to three groups of five volunteers, and 2.0 x 10(7) c.f.u. to 11 volunteers. Diarrhoeal attack rates correlated positively with the size of the inocula (p less than 0.01). It was estimated that a diarrhoeal attack rate of 90% (ED90) would be achievable by inoculation of 1.3 x 10(7) c.f.u. of the organisms. There were no significant differences between the groups in the latent period to positive stool culture, maximum vibrio count per gram of stool and duration of stool positivity. The ED90 of V. cholerae obtained may be used as a challenge dose in subsequent studies on protective efficacy of cholera vaccines in Thai adult volunteers.