Immunity in the Swedish population: diphtheria, tetanus and poliomyelitis.

BACKGROUND: Large-scale vaccination programmes have been carried out for a long time in Sweden, as in many other countries. However, often little is known of the effects of these vaccinations. During 1990 and 1991 a survey of immunity based on a random adult population sample was carried out. The main purpose was to estimate the level of immunity to diphtheria, tetanus and polio of the adult population in Sweden. In total 4800 people were randomly selected according to a stratified, two-stage, sampling plan. METHODS: Based on standard sampling theory, methods for calculations of estimates and confidence intervals of the proportion of the population that is immune are given. The response patterns and its possible effects on the estimates are discussed. RESULTS: In total, 70.6% of the 4800 selected gave a blood sample. The response rate differs for men and women and for different age groups. Among the oldest, the response rate was close to 80%, but it was only about 60% among the youngest. CONCLUSIONS: With the survey design used, it was possible to obtain a sufficient degree of response. Our experience is that the response rate depends to a large extent on the efforts made to explain and motivate participation.

Immunity to tetanus, diphtheria and poliomyelitis in the adult population of Sweden in 1991.

BACKGROUND: During 1990 and 1991 a survey of immunity was carried out in Sweden. The main purpose was to estimate the level of immunity to diphtheria, tetanus and polio in the adult population. In total, 4800 people, randomly selected according to a stratified, two-stage, sampling plan, were contacted and asked to contribute a blood sample. Of those selected, 70.6% gave a blood sample. METHODS: Estimates and confidence intervals of the proportion of the population with antibodies exceeding some titre was calculated. The population was divided according to sex, year of birth (five age groups) and residence (four regions). RESULTS: In age groups that were born after the introduction of childhood vaccination, > or =90% and 75-90% of people have demonstrable antibodies at a protective level against tetanus and diphtheria respectively. Those born earlier, especially women, are poorly protected with less than 50% having protective antibody levels for both tetanus and diphtheria. Differences between men and women were particularly seen in the age groups born between 1930 and 1950. Less than 5% of the Swedish population lacked the protective level antibodies against polio types 1, 2 and 3 respectively. CONCLUSIONS: Vaccination against tetanus, which can be combined with vaccination against diphtheria, can be recommended especially to women born before 1950 and with no documented previous vaccination. The same recommendation can be given for men born before the 1930s. As regards poliomyelitis, general booster vaccination of the adult population does not appear to be necessary at present.

Immunity to measles before and after MMR booster or primary vaccination at 12 years of age in the first generation offered the 2-dose immunization programme.

In 1982, a 2-dose regimen was introduced in Sweden for the combined vaccination against measles, mumps and rubella (MMR) in children aged 18 months and 12 years. In 1993, blood samples from 378 12-year-old children, i.e. the first age-group receiving a MMR booster, were collected prior to and 2 months after the vaccination. 82% had a certificate of a previous measles (M) or MMR vaccination (group I). The remainder was classified as children with 'no documentation' (group II). In group I, 5 (1.5%) lacked demonstrable antibodies to measles prior to the booster; in group II this figure was 39%. The pre-booster antibody pattern was similar in M vaccinees and MMR vaccinees. After the vaccination, 1 of the 378 children was seronegative. In both groups, children with low pre-vaccination levels responded with a titre rise, in accordance with a similar study 6 years earlier.

Immunity to mumps before and after MMR vaccination at 12 years of age in the first generation offered the two-dose immunization programme.

Sweden was the first country in the world to introduce a two-dose programme of vaccination against measles, mumps and rubella with a combined vaccine (MMR). It was commenced in 1982 and the vaccination was carried out at the ages of 18 months and 12 years. In 1992-93 the first age-group vaccinated at 18 months reached the age of 12 and accordingly received a second dose of MMR. A total of 382 children participated in the present study. Sero-immunity against mumps was studied by testing neutralizing antibodies using serial dilutions inoculated into cell cultures before and after the 12-year vaccination. Of the 229 children earlier vaccinated (group A), 27% lacked demonstrable antibodies before the booster. Of those without documented vaccination records (group B), 56% were seronegative before vaccination. After vaccination, 93% of group A and 86% of group B were seropositive (titre > or = 2). In the seronegative children, whether vaccinated earlier or not, the seroconversion was ca 75%. Previously unvaccinated children positive before vaccination and thus likely to be naturally immune had a higher mean-titre both before and after vaccination than the seropositive children earlier vaccinated. So far, the two-dose programme has proceeded as expected.

The prevalence of hepatitis B in Sweden; a statistical serosurvey of 3381 Swedish inhabitants.

The prevalence of hepatitis B virus markers in the adult Swedish population was investigated according to age, sex, origin and demographic stratum. Sera were collected from 3382 persons in 1990-1. The sera were selected on a statistical basis considered to be representative of the Swedish population from adults aged > or = 18 years. Two of the sera (0.06%) were found to be hepatitis B surface antigen positive. The two hepatitis B carriers were of non-Scandinavian origin as were (8.9%) of those tested. A total of 90 persons had a marker of previous, hepatitis B virus infection, i.e. antibodies against hepatitis B core antigen. Of these, 66 (2.0%) were of Scandinavian origin and 24 (18.1%) from highly endemic areas. The overall hepatitis B virus marker prevalence was 2.7%. The highest age-specific prevalence of hepatitis B markers in those of Scandinavian origin was in those born in 1939 and earlier. In this age-group, women had a significantly higher prevalence (3.6%) than males (1.9%). The lowest prevalence was found in those born in 1970 and later. No significant, age-related differences between younger or older persons, or between men and women, could be found in persons of non-Scandinavian origin. The results showed significant differences in exposure to hepatitis B virus among the indigenous population, compared with those of non-Scandinavian extraction. The results do not support the proposal to include hepatitis B vaccination in the Swedish immunization schedule.

Twenty years' experience of rubella vaccination in Sweden: 10 years of selective vaccination (of 12-year-old girls and of women postpartum) and 13 years of a general two-dose vaccination.

Two different strategies for the prevention of rubella-induced malformations have now been practised in Sweden, both reaching 90% or more of the target populations. The first was initiated in 1973-1974 and targeted schoolgirls, susceptible women after pregnancy and women at special risk. The second programme-a two-dose measles, mumps, rubella vaccination (MMR) of both boys and girls at the ages of 18 months and 12 years-was introduced in 1982. The percentage of susceptible pregnant women was gradually reduced from 12% in 1975 to 2.8% in 1987 and to just below 2% in 1994. The majority of the non immune are unvaccinated, these being either Swedes born before 1963 or immigrants. Before 1974 on average 14 severely rubella damaged children were reported yearly. Between 1975 and 1985 only a mean of two cases per year were recorded. Since 1985 no child with the rubella syndrome has been registered.

Hepatitis A immunity in the Swedish population. A study of the prevalence of markers in the Swedish population.

After a 20-year interval, the prevalence of seroimmunity to Hepatitis A (HA) was again investigated in a statistical sample of the adult Swedish population. Sera from 3382 of the 4800 originally selected persons were tested. The prevalence of antibodies to HA had not changed since the 1960s when only the Scandinavian population was considered. In the oldest population born at the beginning of this century, the presence of antibodies amounted to 69%. It gradually declined to 6% in those born in the 1940s. In the population born after 1950, the percentage of seropositive individuals was only 2%. A slightly higher prevalence was seen in the big cities, compared with the rural areas (13% vs 9%). Persons of non-Scandinavian origin showed a different pattern. Those from other European countries showed a prevalence of about 70% in all the age-groups investigated. Among the young adults of Arabic or Asiatic origin, the figure was > 90%. The conclusion is that the native Swedish population has a low natural exposure to HA, which has not changed during the last 20 years. Prophylaxis before going to countries where the disease is endemic is strongly recommended.

Immunity to rubella before and after vaccination against measles, mumps and rubella (MMR) at 12 years of age of the first generation offered MMR vaccination in Sweden at 18 months.

In 1982, a two-dose programme of vaccination against measles, mumps and rubella (MMR) at the ages of 18 months and 12 years was introduced in Sweden. In 1992-3, the first group of children vaccinated at 18 months reached the age of 12, i.e. the time for a second dose. In connection with this 12-year vaccination, 376 children were recruited, investigated concerning earlier MMR vaccination and bled prior to and 2 months after the immunization. Two hundred and twenty of them had a documented, earlier MMR vaccination and 156 had not. The latter were classified as unvaccinated. The antibody status against rubella was measured by the haemolysis-in-gel method. Prior to the present vaccination, 3% of the earlier vaccinated group totally lacked any sign of antibodies. In the presumably unvaccinated group, this figure was 76%. After the vaccination all children showed signs of antibody activity and reached the antibody level of > or = 15 international units, i.e. in our tests a zone dia. of approx 8 mm. However, the secondly vaccinated children ended up with a mean antibody level of 10.7 mm which was slightly lower than the level, i.e. 11.0 mm of those lacking earlier vaccination history and prevaccination seronegative. The earlier unvaccinated but pre-immune children reached a mean level of 11.2 mm. In general, those with relatively high, pre-vaccination, antibody levels reacted less to the booster than those with low or no pre-vaccination immunity. The booster thus appeared to restore the antibody levels of the low-titre children.

Mortality among HIV-infected intravenous drug addicts in Stockholm in relation to methadone treatment.

The aim of the study was to estimate the mortality rate and evaluate the causes of death in all diagnosed HIV-positive IDUs in the Stockholm area, 1986-90, and to compare the risk of death of those who received methadone treatment with that of those never admitted to or discharged from the programme. Data were collected from the Swedish National Bacteriological Laboratory, the Methadone Maintenance Programme (MMTP) and the Department of Forensic Medicine, as well as from hospitals in the Stockholm region. In Sweden 90% of all IDUs are HIV-tested. Most deceased IDUs are examined forensically. This examination always includes HIV-testing. During the observation period, 472 HIV-infected IDUs were reported from the Stockholm area. Of these addicts 135 participated in the methadone maintenance programme for a shorter or longer time during the study period. Most of them had received the HIV-diagnosis more than 1 year before first entering the programme. Sixty-nine subjects died during the observation period. A majority, 52 persons, died from violence or poisoning. Seventeen died from somatic complications of drug abuse. Nine of them were diagnosed as suffering from AIDS. Eight of the deceased had participated in the MMTP. The relative risk of death from external violence and poisoning was 0.25 (95% confidence interval 0.1-1.0) when participants in the MMTP were compared with HIV-infected IDUs never attending the programme. When all causes of death are compared the relative risk was 0.8. Those patients discharged from the programme have a higher mortality rate than those who never participated.(ABSTRACT TRUNCATED AT 250 WORDS)

The AIDS epidemic among Scandinavian women: 1980-1990.

OBJECTIVE: To describe trends and patterns in the AIDS epidemic among Scandinavian women with AIDS. SUBJECTS AND METHODS: All women with AIDS reported to national surveillance units in Denmark, Norway and Sweden in 1980-1990 were included for analyses. RESULTS: The number of heterosexually infected female AIDS cases increased over time. AIDS-defining diseases varied with transmission categories, a variation similar to that found among heterosexual Danish male AIDS cases. Heterosexually infected women were more frequently diagnosed with Pneumocystis carinii pneumonia than with oesophagus candidiasis compared with intravenous drug using women. Twenty-five out of 56 heterosexually infected women reported having a male partner who was bisexual or from a Pattern II country, while one in four did not recognize any risk in their sex partner(s). Survival time increased between 1980 and 1990 and did not differ from survival in male AIDS cases. In a proportional hazards model, age, year of diagnosis and the duration of known HIV-positivity before development of AIDS had an independent impact on survival. The number of women known to be HIV-positive for more than 1 year before diagnosis of AIDS increased over time, although the number of women tested for HIV close to the development of AIDS was especially high among heterosexually infected women. CONCLUSION: Increasing numbers of heterosexually infected women are being diagnosed with AIDS in Scandinavia.