National serosurvey of poliovirus immunity in Australia, 1996-99

OBJECTIVE

To measure immunity to poliovirus types 1, 2 and 3 in the Australian population.

METHODS

Sera were collected opportunistically from laboratories around Australia between 1996 and 1999. A representative sample by age and gender was tested for neutralising antibodies to poliovirus types 1, 2 and 3. A titre of > or = 8 was considered antibody positive and indicative of immunity.

RESULTS

Of the 1,813 sera tested, 82% were antibody positive for poliovirus type 1 and 88% were positive for type 2. Immunity to type 3 poliovirus was lower overall (74%) and especially in school-aged children and young adults. For all three poliovirus types, there were more females immune than males and immunity peaked in the 2-4 years age group. The proportion of the population immune to all three types was 59%, and 3% were negative for all three types.

CONCLUSIONS AND IMPLICATIONS

This is the first national serosurvey for immunity to poliovirus in Australia. Herd immunity is probably sufficient to prevent generalised outbreaks due to type 1 and 2 poliovirus, but this may not be the case for type 3. However, localised outbreaks of any poliovirus type could still occur following reintroduction unless uniformly high levels of vaccination coverage are maintained. Ongoing serosurveillance is required following the recent change back to inactivated polio vaccine.

Immunity to poliomyelitis in Victorians

OBJECTIVES

In view of WHO's goal for poliomyelitis eradication by 2005 and the possible introduction of IPV into the Australian Standard Vaccination Schedule, this investigation was conducted to assess current immunity to poliomyelitis across the Victorian community.

METHODS

1,775 sera collected from three population samples within the Victorian community between 1990 and 1995 were tested for neutralising antibody titres against each poliovirus type in accordance with WHO recommended procedure.

RESULTS

In infants over three months and adults under 40 years, 76-100% of people in each age group were seropositive to all poliovirus types, with 90-100% seropositive to type I, 94-100% seropositive to type II and 80-97% seropositive to type III. Of the very small number of adults over 40 years tested (n = 13), 85% were seropositive to each of types I and II, and 62% to type III. 92% of vaccination histories taken and checked were confirmed, and reported immunisation rates were significantly below seropositive rates.

CONCLUSIONS

According to poliovirus antibody seroprevalence, current immunity to poliomyelitis appears sufficient for herd immunity. When compared with vaccination histones, significantly more people demonstrated immunity to poliomyelitis than the number who reported having been vaccinated against it, indicating the possible role of intestinal vaccine strain poliovirus spread in maintaining high immunity levels.

IMPLICATIONS

The current Australian Standard Vaccination Schedule has successfully provided protective levels of poliomyelitis immunity for the Victorian community in the absence of wild virus since at least 1972. This must be considered in assessing the future direction of Australia's poliomyelitis immunisation program.

Decline in immunity to polio among young adults

A serologic survey was conducted on a population-based representative sample of 521 18-year-old soldiers recruited to the Israel Defence Forces in 1997. The prevalence of neutralizing antibodies and geometric mean titers (GMTs) against the three types of poliovirus (Mahoney, MEF and Saukett strains) were found to be 98.7% (GMT--169.95), 99.6% (GMT--297.14) and 96.4% (GMT - 59.48), respectively. These GMTs are markedly lower than those recorded 4 years after booster vaccination carried out during a 1988 polio outbreak, and suggest a decline in immunity against polio among young adults. These findings support the policy of routine revaccination of children and adolescents in countries at risk of imported polioviruses and of revaccination of adults traveling to areas to which polio is endemic.

Acquisition of immunity in mothers of infants administered trivalent oral poliovirus vaccine

The hypothesis that live oral poliovirus vaccine (OPV) confers immunity to persons in close contact with the vaccine recipient was tested by comparing cord blood antibody titers in 31 first-born neonates to those of 48 neonates with one or more siblings adequately immunized with OPV. A borderline or negative result (defined as a reciprocal titer of < or = 8) for at least one type was significantly more prevalent among first-born neonates than among neonates with one or more siblings [17/31 (55%) versus 17/48 (27%) respectively; p < 0.03]. This difference was consistent for all three poliovirus types. The geometric mean titer (GMT) was consistently higher for each serotype in infants with one or more siblings compared with first-born neonates: 134.9 versus 64.5 for poliovirus 1; 262.1 versus 95.6 for poliovirus 2; and 48.6 versus 19.4 for poliovirus 3, respectively. When cord blood of neonates with two or more siblings was compared to that of neonates with only one sibling, no difference in titers was observed. Since mothers of one or more infants were on average older and less educated, the results were adjusted accordingly, but the same trend was observed again. These findings support the notion that OPV is important, not only as a vaccine for the individual infants, but also as a means of conferring immunity to persons in close contact.

Age differences in immunity against wild and vaccine strains of poliovirus prior to the 1988 outbreak in Israel and response to booster immunization

During the 1988 type 1 polio outbreak in Israel, most cases occurred in previously vaccinated subjects aged 11-30 years, suggesting a possible age-related immunity deficit against the wild virus responsible for the outbreak. We examined type 1 poliovirus neutralizing antibody titres against the Sabin strain, the standard wild strain (Mahoney), the wild strain responsible for the 1988 outbreak and a previous wild strain from the region, on frozen sera drawn prior to the mass vaccination campaign from subjects aged 6 to 40 years. Response to vaccination with oral poliovaccine (OPV) was examined in a subgroup aged 18-40 years. At all ages, the highest antibody titres prior to the outbreak were against the Sabin strain. Geometric mean titres (GMTs) against both the Sabin strain and the wild Mahoney strain were significantly higher in the age groups 6-7, 12-13 and 30-40 years compared with the 18-29-year-olds. For the other wild strains, the GMT for those aged 30-40 years was significantly and substantially higher than in the other age groups, followed by the 12-13- and 6-7-year-olds and lowest in those aged 18-29 years. Following vaccination with OPV in subgroups aged 18-29 and 30-40 years, GMTs against Sabin and all wild strains were similar to each other and in both age groups. These findings suggest that there was a relative immunity gap against the wild type 1 strains in the age group that lacked prior exposure to wild virus and had received the last OPV dose more than 17 years previously.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunization status of casualty attenders: risk factors for non-compliance and attitudes to 'on the spot' immunization

Outbreaks of vaccine preventable infections have focused attention on 'missed opportunities' for immunizing children. The immunization status of 520 consecutive children attending Casualty during a 10 day period was studied. Only 70% of children had received their diphtheria, tetanus, pertussis (DTP) and poliomyelitis immunization at the appropriate time, 13% had completed the schedule later than recommended and 17% had immunizations overdue by 4 weeks or more. For measles (mumps/rubella) vaccine (MM or MMR) 75% were up to date, 10% were given late and 15% were overdue. A subset of 171 families was interviewed to evaluate factors affecting compliance. Families possessing a Social Security 'Health Care Card', whose father was unemployed, who spoke poor English or who had lived in Australia for 5 years or less were significantly more likely (P < 0.02) to be inadequately immunized. There were 84 children whose immunization was overdue and who were well enough to be immunized. The parents of 70 (83%) of these 84 said that they would agree to 'on the spot' immunization if it were available; 14 (17%) parents refused, the commonest reason for refusal being that the parents felt that the child was too sick at the time to be immunized.

Preventive health behaviours among parents of infants aged four months

Six preventive health behaviours have been frequently identified as having the potential to reduce mortality and morbidity during infancy: breast-feeding until the age of six months; no solid food until after four months of age; immunisation against whooping cough, diphtheria, poliomyelitis and tetanus; the use of a baby capsule to restrain the infant when travelling in a motor vehicle; regular attendance at a health care provider for preventive health checks; and no maternal smoking. This study surveyed 191 primiparous women four months after the birth of their babies to explore the proportion of parents who perform the recommended preventive health behaviours and the association among the behaviours. Thirty-nine per cent of the women reported that they were no longer breast-feeding by the time their infant was four months old; 35 per cent had introduced solids before 16 weeks of age; 35 per cent did not always use a baby capsule when travelling with their baby in their car, 25 per cent did not regularly attend the early childhood health centres and 22 per cent smoked. Forty-eight per cent of the sample were performing four or fewer of the six preventive health behaviours and 21 per cent were performing three or fewer. The relationship between performing each preventive health behaviour and a range of demographic variables was investigated. A logistic regression indicated that performing three or fewer of the health behaviours was associated with lower levels of education, having public health insurance and being born in a country other than Australia.

A hepatitis B vaccination programme for inner metropolitan Sydney neonates

OBJECTIVE; To review the effectiveness of a hepatitis B vaccination programme for high risk infants within a mobile urban population.

DESIGN

A follow-up study of 1429 infants enrolled consecutively in the programme from September 1987 to December 1988.

SETTING

The programme was established in early childhood centres within inner metropolitan Sydney, an area where 30% of residents were born in non-English speaking countries and where doubts had previously been expressed about the efficacy of vaccination.

PARTICIPANTS

Neonates born to mothers who were surface antigen positive, born in selected countries with a 5% prevalence of surface antigen carriage, Aboriginal or intravenous drug users.

OUTCOME MEASURES

Documented vaccination given by early childhood centre nurses. Some adjustment was made for parents' reports of vaccination given elsewhere.

RESULTS

Two vaccinations were given to 87% and three to 73% of these infants. If we include vaccinations apparently given elsewhere we estimate that 92% may have been fully protected.

CONCLUSION

The programme produced high rates of compliance with vaccinations within a population where the delivery of such a service was thought to be difficult. Experience with the current State policy for hepatitis B vaccination indicates that it may not optimally reduce the pool of surface antigen carriers within our community.

Immunisation state and its documentation in hospital patients

Two prospective surveys of the immunisation state and its documentation were conducted among children under 2 years old attending a children's hospital. A survey of 111 children attending the casualty or outpatient departments showed that, according to reliable records, 106 (95%) were fully immunised for age with oral polio vaccine, 93 (84%) with triple antigen, and 26 of 33 children greater than or equal to 16 months of age (79%) with measles-mumps vaccine. A survey of 204 inpatients showed that, according to verified records, significantly fewer inpatients than outpatients were fully immunised for age with oral polio vaccine (176, 86%) and with triple antigen (144, 71%). The proportion of inpatients vaccinated with measles-mumps vaccine was 81% (48 of 59). The inpatient figures are all lower than the 95% goal of current child immunisation programmes. Although parents of 98% of inpatients had a personal health record for the child, it was available at the time of admission for less than half the children. Lack of use of the personal health record by admitting medical staff was reflected in incorrect or absent documentation of the immunisation state in 17 of 49 (35%) of the records of children verified to have inadequate immunisations. Parents and health care staff need to be educated in the optimal use of the personal health record. Hospital paediatric staff need to be encouraged to verify the immunisation state of all young children, on admission, and arrange to rectify any deficiency found.

Determinants of partial participation in the immunization programmes in Iran

Results of 45 cluster sample surveys to evaluate the immunization coverage in Iran during 1986 is reported. Overall, 55% of children between the ages of 12-23 months have complete immunization. Apart from mothers' knowledge and motivations, residence in the rural areas and utilization of antenatal care show positive association with immunization coverage. On the other hand, maternal tetanus immunization, hospital delivery and education of birth attendants for deliveries outside hospital, and the sex of the child do not seem to be associated with the child's immunization status. These and other results are discussed.

Impact of rubella vaccination in Australia

Rubella vaccination of schoolgirls aged 10-14 years started 13 years ago in Australia; the girls were vaccinated without prior assessment of their immunity. Non-pregnant seronegative women were also offered vaccination in family-planning clinics and post partum in obstetric units. Serological follow-up of 191 schoolgirls 5 years after vaccination and 56 girls 8 years after vaccination showed that all had detectable rubella antibody, whereas 24% of 239 unvaccinated young men of similar age (18-23 years) were seronegative. In 1983, 96% of 8226 pregnant women aged 12-53 years (mean 25.3 years) had detectable rubella antibody, and since 1977 there has been a striking reduction in the incidence of deafness due to congenital rubella. These results indicate that the rubella vaccination programme in Australia is having a significant impact on both the serological status of pregnant women and on the incidence of congenital infection.

Population studies of diphtheria immunity using antitoxin radioimmunoassay

A quantitative method for testing serum diphtheria antitoxin levels was set up using a diphtheria antitoxin radioimmunoassay (RIA). The results of this RIA correlated well with the Schick test in 554 subjects and with intradermal neutralization tests in guinea-pigs in a small group of subjects. The RIA was suitable for use on blood collected by fingerprick on to a disc of standard chromatography paper. These discs could be stored at room temperature for at least 1 month. If storage for more than 6 months was required -20 degrees C was found to be better. Experience with this RIA in a total of 2349 subjects indicated that it is more accurate, rapid and less costly than Schick testing. The RIA should prove to be the preferred method for testing diphtheria immunity in population surveys.

Immunity to poliomyelitis in Sydney's children

No indigenous cases of poliomyelitis have occurred in New South Wales since 1970, and it was presumed that herd immunity was high. However, our survey of Sydney's children by the neutralization test showed that only 42% of children had antibody levels (titre 8 or higher) to all three serotypes, 30% had antibodies to two, 16% to one, and 12% had no demonstrable antibodies at all. The immune status could not be determined with confidence from the immunization history, as 48% of the children who were reported as having received four or more doses of Sabin vaccine were not fully immune. When children who had inadequate levels of antibodies were given a single dose of Sabin vaccine, 77% of them achieved adequate antibody levels to all three viruses. The Health Commission of New South Wales subsequently undertook a mass Sabin immunization campaign of primary-school children, and reviewed the recommended immunization schedule.

Diphtheria immunization in adolescents and adults with reduced doses of adsorbed diphtheria toxoid

A study was undertaken in Schick-positive university students and schoolchildren to determine the diphtheria antitoxin response to vaccines containing a reduced dose of adsorbed diphtheria toxoid. It was found that the majority of participants, apparently previously sensitized, responded with an increase in antitoxin titre to protective levels after performance of the Schick test, or after the first dose of vaccine. A group of non-immune students required three doses of vaccine to reach adequate antitoxin levels to ensure durable immunity. Only one local reaction was observed in the group of 51 students, and this was attributed to an Arthus-type reaction involving the tetanus toxoid component of a combined adsorbed diphtheria and tetanus vaccine.