Universal immunization of infants with low doses of a low-cost, plasma-derived hepatitis B vaccine in South Africa.

OBJECTIVE: To evaluate the effectiveness of universal vaccination against viral hepatitis B in South Africa among 18-month-old rural children. METHODS: Children were immunized with a course of low-dose (1.5 microg), plasma-derived hepatitis B vaccine at 6, 10 and 14 weeks of age, and blood samples from the children were tested for three hepatitis B markers: hepatitis B surface antigen (HBsAg), anti-HBs and anti-HBc. FINDINGS: One year after vaccination, a protective anti-HBs antibody titre of at least 10 IU/l was present in 669/769 (87.0%) of blood serum samples tested. Only 3/756 children (0.4%) were HBsAg positive and a fourth child was anti-HBc positive (HBsAg negative). This is a marked decrease compared to the hepatitis B prevalences reported in previous studies. Among rural migrant mine-workers, for example, HBsAg prevalence was 9.9%, and was 10.1% among children 0-6 years of age in the Eastern Cape Province. CONCLUSION: The low-dose, plasma-derived hepatitis B vaccine, which is affordable to most developing countries, was very successful in controlling endemic hepatitis B infection, where the virus is predominantly spread by horizontal transmission among infants and young children.

Seroprevalence to polio in personnel at a virology institute.

OBJECTIVES: To determine the level of immunity to polio in adult personnel at the National Institute for Virology (NIV), South Africa. METHODS: Polio neutralizing antibodies results on 776 NIV staff members tested between 1979 and 1999 and seroresponses in seronegative personnel given a booster vaccination were analysed. RESULTS: 613 of the 776 (79%) personnel had neutralizing polio antibodies to all three types, independent of age, gender, race or job category. Types 1 and 2 antibodies were found in 92% and 94%, respectively, but type 3 was less prevalent at 87%. Of the 93 persons seronegative to one or more types, 13 failed to respond to the first booster vaccination and 8 remained as non-responders after two booster vaccinations. Of the 19 personnel who were bled four days after booster vaccination, 16 (84%) had already developed an antibody response. CONCLUSIONS: Most (79%) adult laboratory personnel retained detectable levels of neutralizing antibodies to polio, independent of age, gender, race or job category, and even in those persons lacking detectable antibodies, most (84%) responded with a secondary immune response. Nevertheless the immunity gap, particularly to type 3, mandates routine screening of personnel potentially exposed to wild-type polio virus and a booster vaccination for seronegatives.

Impact of the introduction of A/Sydney/5/97 H3N2 influenza virus into South Africa.

In 1998 South Africa experienced a major influenza epidemic that was characterized by extensive illness and an unusually early season. The impact of the epidemic was charted by measuring proxy indexes of influenza activity such as school absenteeism and excess mortality in persons older than 65 years. Viruses isolated from patients of all age groups were analyzed both antigenically and at the molecular level to determine the characteristics of the influenza strain responsible for the outbreaks. The study revealed that influenza activity was detected as early as the middle of April and peaked toward the end of May and early June. School absenteeism correlated with a sharp rise in virus isolation during this period. Consumption of influenza-related pharmaceuticals, as well as mortality figures, also corresponded to the increased absenteeism and virus isolation. Characterization of the viruses isolated during 1997 and 1998 showed clearly that the epidemic was caused by the introduction of the A/Sydney/5/97-like H3N2 influenza strain into South Africa in 1998. With no prior exposure to this virus strain, which is antigenically distinct from the viruses that had been present in this country in 1997, the population was highly susceptible, resulting in an early, rapid spread of influenza. This epidemic has highlighted the importance of having an influenza vaccine specifically formulated for the Southern Hemisphere. If the 1998 vaccine had not contained the A/Sydney/5/97 strain, the widespread outbreaks in South Africa would have been far worse in terms of morbidity, mortality, and economic loss. This, in turn, emphasizes the need for increased influenza surveillance and international cooperation.

Genetic stability of oral polio vaccine prepared on primary monkey kidney cells or Vero cells--effects of passage in cell culture and the human gastrointestinal tract.

The genetic stability of the three Sabin oral poliovaccine (OPV) strains produced on either primary monkey kidney (VK) or Vero cell substrates was compared in vivo and in vitro by measuring the rate at which the bases most strongly associated with attenuation and reversion to neurovirulence (positions 480, 481, and 472 in the 5' non-coding region of Sabin 1, 2 and 3 respectively, and 2034 in VP3 of Sabin 3) reverted during passage of the vaccine strains in the gastrointestinal tract of primary vaccinees and in cell culture. For the in vivo study, the poliovirus excretion patterns of 21 infants receiving OPV produced on either VK or Vero cells were followed for 21 days. No significant differences in either the frequency of excretion or the rate of reversion were observed between the two vaccine groups. The rate of accumulation of revertants during passage in vitro was compared for the three Sabin strains passaged 10 times in either VK or Vero cells. For types 1 and 3, revertants accumulated faster upon passage through VK cells compared with passage through Vero cells. Type 2 appeared to be stable as no revertants were detected in either cell type. Results of this study suggest that the use of Vero as opposed to VK cells as substrate for the manufacture of OPV does not negatively influence the genetic stability of the three Sabin OPV strains in vivo or in vitro.

False negativity by an anti-HIV assay kit (IMx 8B32) and evaluation of its replacement (IMx 8C98).

False negativity in a commercial anti-HIV kit (IMx HIV-1/HIV-2 3rd Generation Plus (code 8B32) was investigated, and the kit that superseded it (IMx HIV-1/HIV-2 III Plus, code 8C98) was evaluated. In a comparison on 574 freshly collected anti-HIV-1-positive specimens, 97.2% were more reactive in 8C98 than in 8B32; 35.5% were more than twice as reactive and 8.5% were more than four times as reactive. In 8B32, the signal from 55 specimens selected because of weak reactivity was enhanced 1.5 to 8.8 times by preliminary heating at 56 degrees C for 30 min. The reactivity of the 55 heated sera was then similar to that of the same specimens tested without heat treatment in the 8C98 assay. Reactivity in 8B32 was also increased in 66 of 76 (at least twofold in 20) randomly chosen anti-HIV-positive serum specimens by the addition of EDTA (10 mM final concentration). One of these specimens was false negative (signal:cutoff (S:CO) ratio 0.76) in 8B32, though its reactivity was restored by addition of EDTA (S:CO ratio 9.54). These findings indicate that the inhibitory effect that originally led to false negative findings in 8B32 was probably due to complement activity, and that the same activity was present in the freshly collected specimens used here to evaluate the replacement IMx anti-HIV assay (8C98). The specimen panel employed to evaluate 8C98 included 1,892 anti-HIV-positive and 779 anti-HIV-negative specimens. There were no false negative reactions. The lowest S:CO ratio observed was 6.2 and only 17 (0.2%) anti-HIV-positive specimens gave ratios less than 10. Nine unreproducible false positive reactions arose, all possibly attributable to specimen carryover by the IMx instrument. The performance of 8C98 was also compared with that of 10 other current anti-HIV kits using 21 sets of seroconversion specimens (127 specimens in total), and five performance assessment panels (92 specimens in total) comprised mostly of single bleeds from recent seroconverters. IMx 8C98 was the second most sensitive assay. We found no evidence that the 8C98 kit was prone to the effect that had given rise to false negative results in its predecessor (8B32).

A population-based seroprevalence study in South Africa as a tool in the polio eradication initiative.

A seroprevalence study for poliomyelitis was carried out on a sample of sera from a serum bank used for a vitamin A study. Vaccination coverage was satisfactory (80% or more) in five of nine provinces, although a prevalence of antibody to polio of 80% or more was found in all provinces. Serologic immunity (i.e., the prevalence of neutralizing antibodies) exceeded vaccination coverage, suggesting secondary spread of vaccine virus. However, whether or not water was supplied through a piped system was not associated with secondary spread of vaccine virus to nonvaccinated children. Seroprevalence studies are a valuable adjunct to acute flaccid paralysis surveillance, which is the standard surveillance instrument for the poliomyelitis eradication initiative. The use of available and suitable serum banks for seroprevalence investigations is a relatively cheap monitoring option that can yield very valuable information for the eradication initiative.

Evaluation of the MUREX*ICE HIV-1.O.2 capture enzyme immunoassay for early identification of HIV-1 seroreverting infants in a developing country.

BACKGROUND: A simple, inexpensive serological assay is required for the early determination of HIV infection status among infants born to HIV-1-seropositive women in developing countries. OBJECTIVES: To evaluate the use of a commercially available capture enzyme immunoassay (EIA), the MUREX*ICE HIV-1.O.2, for the early identification of seroreverting, uninfected infants. STUDY DESIGN: Infants with a clearly defined HIV-1 infection status, as determined by polymerase chain reaction results and/or seroreactivity at 18 months, were tested for antibodies to HIV. The time to seroreversion using the capture EIA was compared with the results obtained using an indirect assay, the GENELAVIA MIXT EIA. RESULTS: Seroreverting infants were identified earlier with the capture than the indirect EIA; all of the uninfected infants were seronegative at 12 months with the capture EIA while 100% seroreversion was only seen at 18 months with the indirect EIA. CONCLUSIONS: In general, the capture EIA identified seroreverting infants 3-6 months earlier than the indirect EIA. However, caution must be exercised in interpreting seroreactivity in a breast-fed population where HIV infection may occur in a child who has previously seroreverted.

Molecular characterisation of type 1 polioviruses associated with epidemics in South Africa.

The molecular epidemiology of wild-type 1 polioviruses isolated in South Africa during 2 major poliomyelitis epidemics in the 1980s and during the pre- and inter-epidemic periods was investigated by partial sequence analysis across the VP1/2A junction. Poliovirus-specific primers were used to amplify and subsequently sequence the region of interest. Viruses belonging to different genotypes were found to have been responsible for the 2 outbreaks. The Gazankulu outbreak in 1982 was caused by a poliovirus genotype which was unique to South Africa and which circulated endemically throughout much of the country between 1980 and 1985. Two additional genotypes, imported from the Middle East and West Africa, cocirculated endemically with the South African genotype between 1982 and 1985. The 1988 epidemic in Kwazulu-Natal was attributed to an imported genotype apparently introduced into South Africa in 1985 from countries north of the border. This genotype displaced the 3 genotypes previously in circulation and continued to be transmitted within the country until 1989, when the last confirmed cases of poliomyelitis associated with wild-type viruses were documented. All circulating wild-type poliovirus strains appear to have been eliminated from South Africa.

Molecular epidemiology of type 1 polioviruses from Africa.

The genetic relationships between type 1 polioviruses circulating in sub-Saharan Africa during the past decade have been investigated by partial genomic sequencing across the VP1/2A region of the polioviral genome. Sequencing templates were generated by single-step reverse transcription PCR amplification of the viral RNA using poliovirus-specific primers. Seven poliovirus genotypes, circulating in different geographical regions during different periods, were identified. Considerable genetic variation was exhibited by strains within several of these genotypes, indicative of sustained endemic transmission within individual countries. Two genotypes appear to be circulating in Africa at present; one major genotype, which has been in circulation since at least 1980, covers a wide geographical region and includes countries in western, central and southern Africa. Within this genotype are several smaller clusters, possibly representing strains in the process of evolving into new genotypes. The second genotype presently in circulation has been found only in Tanzania and Zambia to date, associated with a relatively small number of cases. Imported genotypes, introduced from the Middle East and the Indian subcontinent, have also recently been in circulation in eastern and central Africa. In South Africa, three genotypes, one unique to the country and the others imported from west Africa and the Middle East, co-circulated endemically between 1980 and 1985. A fourth genotype, introduced from countries to the north, displaced the endemic strains and continued to circulate until 1989. This study has generated a meaningful overview of the endemic circulation and regional transmission of type 1 polioviruses throughout sub-Saharan Africa.

The molecular characterization of influenza virus strains isolated in South Africa during 1993 and 1994.

Influenza A (H3N2) and influenza B viruses isolated recently in South Africa were analysed by partial nucleotide sequencing of the haemagglutinin gene to examine antigenic drift of the isolates relative to the vaccine strains. The genomic analysis of the influenza B isolates revealed a number of differences in the amino acid residues compared with those of the B/Panama/45/90 vaccine strain, and these isolates were found to be antigenically more closely related to B/Quindao/102/91. In both the 1993 and 1994 influenza A (H3N2) isolates significant drift had taken place compared with the H3N2 vaccine strains for those years, emphasizing the need for an influenza vaccine formulated specifically for the southern hemisphere.

Evaluation of the World Health Organisation antibody-testing strategy for the individual patient diagnosis of HIV infection (strategy III).

OBJECTIVE: To evaluate the World Health Organisation (WHO) antibody testing strategy for the individual patient diagnosis of HIV infection (strategy III). DESIGN: Evaluation of a combination of enzyme-linked immunosorbent assays (ELISAs) for the detection of antibodies to HIV-1 and HIV-2 infection. The WHO strategy III calls for a combination of three ELISAs, based on different antigens and/or differing test principles, to be used in a sequential fashion. The first part of the study evaluated various kits as part of a selection process. The second part of the study was an assessment of the three-ELISA testing strategy on routine sera submitted to the National Institute for Virology (NIV) for HIV testing. In all instances, the conventional testing protocol, which utilises a screening ELISA followed by a confirmatory Western blot (WB) on positive specimens, was used as the 'gold standard'. SETTING: The HIV-testing laboratory at the NIV, Johannesburg. RESULTS: In the first part of the study, all of the ELISA kits evaluated showed high sensitivity and specificity, and a selection of the kits for part two of the study was made in accordance with the WHO recommendation. The kits selected, in order of use, were the Biotest anti-HIV 1/2 (test 1), Pasteur Genelavia Mixt HIV-1/2 (test 2) and Murex Wellcozyme HIV-1 competitive assay (test 3). This combination was evaluated using 7,812 sera submitted to the NIV for serology testing. The sensitivities of the tests were highly satisfactory (99.6-100%) as were the specificities (99.2-100%). The positive predictive value of strategy III at various seroprevalence (0.5-25.5%) was > or = 99.6%. The rate of WB usage when compared with the previous HIV testing protocol was low (4.6%). CONCLUSIONS: The results of this study suggest that this testing protocol could be introduced in South Africa with considerable cost-saving and no reduction in specificity.

Antigenic relationship between chikungunya virus strains and o'nyong nyong virus using monoclonal antibodies.

Chikungunya (CHIK) strains from Africa and Asia were shown to be antigenically closely related using a panel of monoclonal antibodies (mAb) prepared against strains H817 from Africa and PhH15483 from Asia. The one-way antigenic relationship between CHIK and o'nyong nyong (ONN) viruses was demonstrated at the epitope level using the immunofluorescence and haemagglutination inhibition techniques. Results of tests with mAb against ONN virus suggest that, while ONN virus has retained most of the CHIK antigenic sites, many of the ONN epitopes have undergone sufficient conformational change such that mAbs prepared against them do not recognize sites on CHIK virus.

Benefits and limitations of the Witwatersrand influenza and acute respiratory infections surveillance programme.

OBJECTIVE: To establish an ongoing active surveillance programme for acute respiratory infections in general, and influenza in particular. DESIGN: A network of 16 sentinel primary health care providers furnished morbidity information and clinical specimens for virus characterisation supplemented by school absenteeism and regional mortality data. SETTING: General practices, hospital outpatient departments and staff clinics in the Witwatersrand area. PARTICIPANTS: Subjects treated for acute respiratory infections by 7 general practitioners, 1 specialist pulmonologist, 4 paediatric outpatient departments, 1 mine hospital and university, factory and institutional staff clinics. Absenteeism data were obtained from 8 primary and 6 high schools in the region (representing 9,000 pupils). OUTCOME MEASURES: Morbidity information and strain characterisation of influenza isolates as well as other viral respiratory pathogens, school absenteeism, seasonal excess mortality. RESULTS: The most sensitive indicator of influenza activity was virus isolation, which gives an earlier warning signal of an impending epidemic than morbidity or absenteeism parameters. Both morbidity and school absenteeism provided quantitative indicators of the severity of the epidemic. Mortality from all causes showed characteristic winter increases in the 65-year-old and older population which were not seen in younger individuals. Circulating influenza viral strains matched the strains recommended for the vaccine in 1991 and 1992, but not in 1993. CONCLUSIONS: The course and extent of the annual winter influenza epidemic can be charted by means of an active surveillance programme, with sentinel primary health care providers furnishing morbidity data and clinical material from which virus isolations can be made. Antigenic characterisation of the isolates demonstrated that circulating strains may not match recommended strains in northern hemisphere-formulated vaccines and stresses the need for a southern hemisphere vaccine formulation for South Africa. Absenteeism information provides an indicator of the impact of influenza on the economy and excess mortality data emphasise the need for routine immunisation of the elderly.

Outbreak of paralytic poliomyelitis in Namibia.

The last confirmed case of poliomyelitis in Namibia had been reported in 1988. However, between Nov 8, 1993, and Jan 7, 1994, 27 cases of paralytic poliomyelitis were confirmed in the country. The outbreak was limited to the south health region; at least 80% of infants in this region have received four doses of oral poliovaccine (OPV) by the age of 1 year. Acute flaccid paralysis (AFP) was the predominant clinical presentation during the outbreak. The patients' ages ranged from 13 months to 12 years; 24 were younger than 5 years. Of the 26 patients whose vaccine status was known, 14 had received four doses of OPV, 6 had one or two doses, and 6 no vaccine. Genotypic analysis showed 86% homology of outbreak isolates with a 1982 Namibian isolate and west African isolates. Factors that may have had a role in the outbreak include establishment of a pool of susceptible people, rapid urbanisation, inadequate sanitation, poor water supply, and possible endemicity of poliovirus in neighbouring areas. Epidemics can occur in areas of high vaccine coverage. Our findings emphasise the need to improve AFP surveillance activities and the estimation of vaccine coverage to identify areas of potential susceptibility for outbreaks.

The current epidemiology of hepatitis A infection in South Africa: implications for vaccination.

Testing stored sera from various categories of individuals has shown that among the Black population hepatitis A virus (HAV) infection is universal and most adult Black subjects are immune. Infection probably occurs early in life, consistent with the epidemiological pattern seen in the developing world. By contrast, seroprevalence of HAV infection in adult White subjects increases with age, reflecting an epidemiological pattern seen in the developed world. White subjects working in a virological laboratory and White medical students had comparatively low seroprevalences of HAV infection and could therefore represent groups at risk. Hepatitis A vaccine is likely to be available in South Africa in the near future and could be offered to these groups. Pre-vaccination immunity screening would be a cost-effective strategy.

The prevalence of antibodies to the hepatitis A virus in Owambo children.

The prevalence of hepatitis A virus infection, in a population as well as the age at which it is usually acquired reflect the prevailing socio-economic conditions and standards of public hygiene. Infection occurs equally in both the sexes. Black Africans are known to have a high prevalence of hepatitis A virus infection and do acquire the infection early in life. This study documents the age-specific prevalence in Owambo children and confirms an equal sex distribution.