Is vaccination against measles, mumps, and rubella associated with reduced rates of antibiotic treatments among children below the age of 2 years? Nationwide register-based study from Denmark, Finland, Norway, and Sweden.

OBJECTIVES: Previous studies have shown that vaccination against measles, mumps, and rubella (MMR) may have beneficial non-specific effects, reducing the risk of infections not targeted by the vaccine. We investigated if MMR vaccine given after the third dose of diphtheria-tetanus-acellular pertussis vaccine (DTaP3), was associated with reduced rates of antibiotic treatments. METHODS: Register-based cohort study following children from the age of recommended MMR vaccination until age 2 years. We included 831,287 children born in Denmark, Finland, Norway, and Sweden who had received DTaP3 but not yet MMR vaccine. Cox proportional hazards regression with age as the underlying timescale and vaccination status as a time-varying exposure was used to estimate covariate-adjusted Hazard Ratios (aHRs) and inverse probability of treatment weighted (IPTW) HRs of antibiotic treatments. Summary estimates were calculated using random-effects meta-analysis. RESULTS: Compared with only having received DTaP3, receipt of MMR vaccine after DTaP3 was associated with reduced rates of antibiotic treatments in all countries: the aHR was 0.92 (0.91-0.93) in Denmark, 0.92 (0.90-0.94) in Finland, 0.84 (0.82-0.85) in Norway, and 0.87 (0.85-0.90) in Sweden, yielding a summary estimate of 0.89 (0.85-0.93). A stronger beneficial association was seen in a negative control exposure analysis comparing children vaccinated with DTaP3 vs two doses of DTaP. CONCLUSIONS: Across the Nordic countries, receipt of MMR vaccine after DTaP3 was associated with an 11% lower rate of antibiotic treatments. The negative control analysis suggests that the findings are affected by residual confounding. Findings suggest that potential non-specific effects of MMR vaccine are of limited clinical and public health importance for the milder infections treated out-of-hospital in the Nordic setting.

Unexpected vaginal bleeding and COVID-19 vaccination in nonmenstruating women.

The association between coronavirus disease 2019 (COVID-19) vaccination and vaginal bleeding among nonmenstruating women is not well studied. The Norwegian Institute of Public Health followed several cohorts throughout the pandemic and early performed a systematic data collection of self-reported unexpected vaginal bleeding in nonmenstruating women. Among 7725 postmenopausal women, 7148 perimenopausal women, and 7052 premenopausal women, 3.3, 14.1, and 13.1% experienced unexpected vaginal bleeding during a period of 8 to 9 months, respectively. In postmenopausal women, the risk of unexpected vaginal bleeding (i.e., postmenopausal bleeding) in the 4 weeks after COVID-19 vaccination was increased two- to threefold, compared to a prevaccination period. The corresponding risk of unexpected vaginal bleeding after vaccination was increased three- to fivefold in both nonmenstruating peri- and premenopausal women. In the premenopausal women, Spikevax was associated with at 32% increased risk as compared to Comirnaty. Our results must be confirmed in future studies.

Heavy bleeding and other menstrual disturbances in young women after COVID-19 vaccination.

BACKGROUND: Many signals of menstrual disturbances as possible side effects of vaccination against COVID-19 have been reported. Our objective was to compare the risk of menstrual disturbances before and after vaccination among women aged 18-30 years in Oslo, Norway. METHODS: We used electronic questionnaires to collect reports of menstrual disturbances from 3972 women aged 18-30 years, participating in the population-based Norwegian Young Adult Cohort. We examined the occurrence of menstrual disturbances (heavier bleeding than usual, prolonged bleeding, shorter interval between menstruations, longer interval between menstruations, spot bleedings, stronger pain during menstruation, period pain without bleeding) before and after the first and second dose of COVID-19 vaccine. Relative risks (RR) according to vaccination were estimated using a self-controlled case-series design. We performed additional analyses stratified by vaccine brand, contraception/hormone use, and presence of gynecological condition(s). RESULTS: The prevalence of any menstrual disturbance was 36.7 % in the last menstrual cycle prior the first vaccine dose. The RR for heavier bleeding than usual was 1.90 (95 % CI: 1.69-2.13) after the first vaccine dose and 1.84 (95 % CI 1.66-2.03) after the second dose. Increased risks of prolonged bleeding, shorter interval between menstruations, and stronger pain during menstruation were also observed after both doses. The RRs did not differ with vaccine brand, contraception/hormone use, or presence of gynecological condition(s) for any of the menstrual disturbances. CONCLUSION: Menstrual disturbances were common regardless of vaccination. We found increased risk of menstrual disturbances after vaccination, particularly for heavier bleeding than usual, prolonged bleeding, shorter interval between menstruations, and stronger period pain. In the future, menstrual characteristics should be included in vaccine trials.

Determinants of humoral and cellular immune responses to three doses of mRNA SARS-CoV-2 vaccines in older adults: a longitudinal cohort study.

BACKGROUND: Older age is associated with poorer outcomes to COVID-19 infection. The Norwegian Institute of Public Health established a longitudinal cohort of adults aged 65-80 years to study the effects of the COVID-19 pandemic. Here we describe the characteristics of the cohort in general, and specifically the immune responses at baseline and after primary and booster vaccination in a subset of longitudinal blood samples, and the epidemiological factors affecting these responses. METHODS: 4551 participants were recruited, with humoral (n=299) and cellular (n=90) responses measured before vaccination and after two and three vaccine doses. Information on general health, infections, and vaccinations were obtained from questionnaires and national health registries. FINDINGS: Half of the participants had a chronic condition. 849 (18·7%) of 4551 were prefrail and 184 (4%) of 4551 were frail. 483 (10·6%) of 4551 had general activity limitations (scored with the Global Activity Limitation Index). After dose two, 295 (98·7%) of 299 participants were seropositive for anti-receptor binding domain IgG, and 210 (100%) of 210 participants after dose three. Spike-specific CD4 and CD8 T cell responses showed high heterogeneity after vaccination and responded to the alpha (B.1.1.7), delta (B.1.617.2), and omicron (B.1.1.529 or BA.1) variants of concern. Cellular responses to seasonal coronaviruses increased after SARS-CoV-2 vaccination. Heterologous prime boosting with mRNA vaccines was associated with the highest antibody (p=0·019) and CD4 T cell responses (p=0·003), and hypertension with lower antibody levels after three doses (p=0·04). INTERPRETATION: Most older adults, including those with comorbidities, generated good serological and cellular responses after two vaccine doses. Responses further improved after three doses, particularly after heterologous boosting. Vaccination also generated cross-reactive T cells against variants of concern and seasonal coronaviruses. Frailty was not associated with impaired immune responses, but hypertension might indicate reduced responsiveness to vaccines even after three doses. Individual differences identified through longitudinal sampling enables better prediction of the variability of vaccine responses, which can help guide future policy on the need for subsequent doses and their timing. FUNDING: Norwegian Institute of Public Health, Norwegian Ministry of Health, Research Council of Norway, and Coalition for Epidemic Preparedness Innovations.

Cohort Profile: Childhood morbidity and potential non-specific effects of the childhood vaccination programmes in the Nordic countries (NONSEnse): register-based cohort of children born 1990-2017/2018.

PURPOSE: The aim of the NONSEnse project is to investigate the non-specific effects of vaccines and immunisation programmes on the overall health of children by using information from the extensive nationwide registers on health and sociodemographic factors in Denmark, Finland, Norway and Sweden. PARTICIPANTS: The cohort covers 9 072 420 children aged 0-17 years, born 1990-2017/2018 and living in Denmark, Finland, Norway or Sweden. All countries use a unique identification number for its permanent residents, which makes it possible to link individual-level information from different registers. FINDINGS TO DATE: Data collection and harmonisation according to a common data model was completed in March 2022. As a prerequisite for comparing the effects of childhood vaccinations on the overall health of children across the Nordic countries, we have identified indicators measuring similar levels of infectious disease morbidity across these settings. So far, studies pertaining to non-specific effects of vaccines are limited to investigations that could be undertaken using aggregated data sets that were available before the NONSEnse cohort with individual-level information was completely set up. FUTURE PLANS: We are currently performing several studies of the effects on non-targeted infectious disease morbidity across the countries following vaccination against measles, mumps, rubella, diphtheria, tetanus, pertussis, human papillomavirus, rotavirus and influenza. Multiple studies are planned within the next years using different study designs to facilitate triangulation of results and enhance causal inference. REGISTRATION: No clinical trials will be conducted within the NONSEnse project.

Effectiveness of mRNA Booster Vaccination Against Mild, Moderate, and Severe COVID-19 Caused by the Omicron Variant in a Large, Population-Based, Norwegian Cohort.

BACKGROUND: Understanding how booster vaccination can prevent moderate and severe illness without hospitalization is crucial to evaluate the full advantage of mRNA boosters. METHODS: We followed 85 801 participants (aged 31-81 years) in 2 large population-based cohorts during the Omicron BA.1/2 wave. Information on home testing, PCR testing, and symptoms of coronavirus disease 2019 (COVID-19) was extracted from biweekly questionnaires covering the period 12 January 2022 to 7 April 2022. Vaccination status and data on previous SARS-CoV-2 infection were obtained from national registries. Cox regression was used to estimate the effectiveness of booster vaccination compared to receipt of 2-dose primary series >130 days previously. RESULTS: The effectiveness of booster vaccination increased with increasing severity of COVID-19 and decreased with time since booster vaccination. The effectiveness against severe COVID-19 was reduced from 80.9% shortly after booster vaccination to 63.4% in the period >90 days after vaccination. There was hardly any effect against mild COVID-19. The effectiveness tended to be lower among subjects aged ≥60 years than those aged <50 years. CONCLUSIONS: This is the first population-based study to evaluate booster effectiveness against self-reported mild, moderate, and severe COVID-19. Our findings contribute valuable information on duration of protection and thus timing of additional booster vaccinations.

Trends in Antibiotic Use in Danish, Finnish, Norwegian and Swedish Children.

Objective: To compare the use of antibiotics in children in four Northern European countries. Methods: We conducted a register-based study based on individual-level prescription data from national prescription registers. We identified all redeemed outpatient prescriptions for systemic antibiotics in children aged 0-14 years from July 2006 to June 2017 in Denmark, Finland, Norway, and Sweden. We computed incidence rates and incidence rate ratios of treatment episodes with any antibiotic and different antibiotic classes. Results: In 2016/2017, the rates of antibiotic treatment episodes per 1000 person-years in children aged 0-14 years were 429, 284, 219, and 184 in Finland, Denmark, Sweden, and Norway, respectively, and the rate ratios (95% confidence intervals) compared with Norway were 2.33 (2.33-2.34), 1.54 (1.54-1.55), and 1.19 (1.19-1.20) in Finland, Denmark, and Sweden, respectively. The rate of antibiotic treatment episodes declined over time in all countries. The relative reductions in 2016/2017 compared with 2006/2007 were 36% in Finland, 40% in Denmark, 49% in Sweden, and 29% in Norway. Treatment episodes peaked between age 12 and 18 months. The most used antibiotic class was beta-lactamase sensitive penicillins among all children in Norway and Sweden and among children above two years in Denmark, while penicillins with extended spectrum were most used in Finland and among the youngest children in Denmark. Conclusion: In all countries, the use of antibiotics in children declined between 2006 and 2017. However, there were still considerable differences in antibiotic use between otherwise quite similar Nordic countries, with a more than 2-fold difference between the countries with the lowest and highest rates. Interventions to reduce the number of antibiotic treatment episodes in the countries with higher rates could reduce the total antibiotic use.

Hospital Contacts for Infectious Diseases Among Children in Denmark, Finland, Norway, and Sweden, 2008-2017.

Purpose: Comparing rates of childhood infectious disease hospitalisations across countries may uncover areas for improvement in the prevention of severe childhood infections. We compared rates of childhood infectious disease hospital contacts across Denmark, Finland, Norway, and Sweden with the overall objective to elucidate potential differences in burden of disease and in organisational and registration practices. Methods: Using national registries, we estimated incidence rates for infectious disease hospital contacts between 2008 and 2017 among children aged 0-14 years. We investigated the rates for different types of contacts (inpatient or outpatient including emergency room), duration of admission, and by sex. Results: During the study period, the rate of all hospital contacts per 1000 person-years was highest in Sweden (125.2) followed by Finland (87.1), Denmark (79.0), and Norway (62.1). The rates aligned for inpatient contacts with overnight stays; 19.3 (Denmark), 16.6 (Finland), 16.3 (Norway), and 13.0 (Sweden); these were highest in early infancy in all countries. A peak around 1 year of age was seen in all countries except in Sweden. The rates were higher among boys compared with girls in early childhood, after 13 years of age the rates among girls surpassed the boys. Conclusion: Large cross-country differences were observed for outpatient and short-term hospital contacts for infectious diseases, affected by differences in organisational structures and coding practices across and within countries over time. Inpatient contacts requiring overnight stays reflected more comparable levels of severe infections across countries. Childhood infectious disease morbidity was greatest among boys and before 2 years of age.

Concurrent Infection With Multiple Human Papillomavirus Types Among Unvaccinated and Vaccinated 17-Year-Old Norwegian Girls.

BACKGROUND: Whether type-specific human papillomavirus (HPV) infection influences the risk of acquiring infections with other HPV types is unclear. We studied concurrent HPV infections in 17-year-old girls from 2 birth cohorts; the first vaccine-eligible cohort in Norway and a prevaccination cohort. METHODS: Urine samples were collected and tested for 37 HPV genotypes. This study was restricted to unvaccinated girls from the prevaccination cohort (n = 5245) and vaccinated girls from the vaccine-eligible cohort (n = 4904). Risk of HPV infection was modelled using mixed-effect logistic regression. Expected frequencies of concurrent infection with each pairwise combination of the vaccine types and high-risk types (6/11/16/18/31/33/35/39/45/51/52/56/58/59) were compared to observed frequencies. RESULTS: Infection with multiple HPV types was more common among unvaccinated girls than vaccinated girls (9.2% vs 3.7%). HPV33 and HPV51 was the only HPV pair that was detected together more often than expected among both unvaccinated (P = .002) and vaccinated girls (P < .001). No HPV pairs were observed significantly less often than expected. CONCLUSIONS: HPV33 and HPV51 tended to be involved in coinfection among both unvaccinated and vaccinated girls. The introduction of HPV vaccination does not seem to have had an effect on the tendency of specific HPV types to cluster together.

Revaccination with measles-mumps-rubella vaccine and hospitalization for infection in Denmark and Sweden - An interrupted time-series analysis.

BACKGROUND: In a previous cohort study of 4-year-old Danish children, revaccination with the live measles-mumps-rubella vaccine (MMR) was associated with a 16% reduction in the rate of hospitalization lasting two days or longer for non-measles-mumps-rubella infections. AIM: To examine if the introduction of revaccination with MMR at 4 years of age in Denmark (spring 2008) and at 7-9 years of age in Sweden (autumn 2009), at a time when there was virtually no measles, mumps or rubella cases, was associated with a reduction in the rate of hospitalization-for-infection lasting two days or longer at the population level. METHODS: We included 4-year-olds in Denmark and 7-9-year-olds in Sweden. We obtained the number of hospitalization-for-infection lasting two days or longer from nationwide hospital registers. Person-years at risk were approximated from population statistics for each season and year. We performed an interrupted time series analysis using Poisson regression to estimate the change in hospitalization incidence rates following the introduction of MMR revaccination, adjusting for seasonality. We also performed analyses with control series (3-year-olds in Denmark and 4-year-olds in Sweden). RESULTS: Comparing the incidence of hospitalization-for-infection lasting two days or longer after the introduction of MMR revaccination with the expected level without an introduction of MMR revaccination resulted in an incidence rate ratio of 1.07 (95% confidence interval [CI] = 0.89-1.28) for 4-year-olds in Denmark and 0.89 (95% CI = 0.77-1.02) for 7-9-year-olds in Sweden in analyses without controls. Analyses with controls gave similar results. CONCLUSION: This population-level study of the introduction of MMR revaccination in Denmark and Sweden had inadequate power to confirm or refute the findings from an individual-level Danish study of an association between MMR revaccination and a lower incidence rate of hospitalization-for-infection lasting two days or longer.

Time trends in HPV vaccination according to country background: a nationwide register-based study among girls in Norway.

BACKGROUND: Since the human papillomavirus (HPV) vaccine was introduced in Norway in 2009, the vaccine uptake has increased. Whether this increase is similar regardless of the girls' country background is unknown. We examined changes in HPV vaccine uptake from 2009 to 2014 and studied the impact of parental education and income on HPV vaccine uptake according to country background. METHODS: Girls in the first six birth cohorts (1997-2002) eligible for HPV vaccination were identified through the National Registry. Information on HPV vaccination, country background and socioeconomic factors was extracted from the Norwegian Immunisation Registry and Statistics Norway. Risk differences (RDs) and confidence intervals (CIs) were estimated with linear binomial regression. A total of 177,387 girls were included in the study. RESULTS: The HPV vaccine uptake increased from 72.5% in 2009 to 87.3% in 2014. The uptake increased for girls in all country background categories. Highest vaccine uptake was observed in girls with East-/South-East Asian background, 88.9% versus 82.5% in the total population. Vaccine uptake decreased slightly with increasing parental education, RD = - 1.6% (95% CI: - 2.3% to - 0.8%) for highest compared with lowest education level. In contrast, the uptake increased with increasing household income, RD = 4.9% (95% CI, 4.3 to 5.5%) for highest compared with lowest quintile. Parental education had largest impact in girls with Asian background, RD = - 8.1% (95% CI - 10.5% to - 5.6%) for higher vs lower education. The largest impact of household income was observed in girls with background from Middle East/Africa, RD for a 200,000 NOK increase in income was 2.1% (95% CI 1.2 to 3.0%). CONCLUSIONS: The HPV vaccine uptake differed with country background but increased over time in all country background categories. Moreover, the impact of education and income on vaccine uptake differed with country background.

Impact and cost-effectiveness of strategies to accelerate cervical cancer elimination: A model-based analysis.

Following the global call for action by the World Health Organization to eliminate cervical cancer (CC), we evaluated how each CC policy decision in Norway influenced the timing of CC elimination, and whether introducing nonavalent human papillomavirus (HPV) vaccine would accelerate elimination timing and be cost-effective. We used a multi-modeling approach that captured HPV transmission and cervical carcinogenesis to estimate the CC incidence associated with six past and future CC prevention policy decisions compared with a pre-vaccination scenario involving 3-yearly cytology-based screening. Scenarios examined the introduction of routine HPV vaccination of 12-year-old girls with quadrivalent vaccine in 2009, a temporary catch-up program for females aged up to 26 years in 2016-2018 with bivalent vaccine, the universal switch to bivalent vaccine in 2017, expansion to include 12-year-old boys in 2018, the switch from cytology- to HPV-based screening for women aged 34-69 in 2020, and the potential switch to nonavalent vaccine in 2021. Introducing routine female vaccination in 2009 enabled elimination to be achieved by 2056 and prevented 17,300 cases. Cumulatively, subsequent policy decisions accelerated elimination to 2039. According to our modeling assumptions, switching to the nonavalent vaccine would not be considered 'good value for money' at relevant cost-effectiveness thresholds in Norway unless the incremental cost was $19 per dose or less (range: $17-24) compared to the bivalent vaccine. CC control policies implemented over the last decade in Norway may have accelerated the timeframe to elimination by more than 17 years and prevented over 23,800 cases by 2110.

Substantial Decline in Prevalence of Vaccine-Type and Nonvaccine-Type Human Papillomavirus (HPV) in Vaccinated and Unvaccinated Girls 5 Years After Implementing HPV Vaccine in Norway.

Background: In 2009, quadrivalent human papillomavirus (HPV) vaccine was introduced in a school-based single-cohort program targeting 12-year-old girls in Norway. We estimated the impact of the Norwegian HPV immunization program. Methods: Three birth cohorts of 17-year-old girls, 2 nonvaccine-eligible cohorts (born 1994 or 1996) and 1 vaccine-eligible cohort (born 1997) were invited to deliver urine samples. The samples were analyzed for 37 HPV genotypes. HPV prevalence was compared between birth cohorts and between vaccinated and unvaccinated girls within and across birth cohorts after linkage to the Norwegian Immunisation Registry. Results: In total, 17749 urine samples were analyzed. A 42% (95% confidence interval [CI], 37%-47%) reduction in any HPV type and 81% (95% CI, 76%-85%) reduction in vaccine types (HPV-6/11/16/18) were observed in the vaccine-eligible cohort compared to the 1994 cohort. Vaccine types were reduced by 54% (95% CI, 39%-66%) and 90% (95% CI, 86%-92%) in unvaccinated and vaccinated girls, respectively, from the 1997 cohort, compared with unvaccinated girls born in 1994. A significant reduction was also observed for several nonvaccine types. Vaccine-type prevalence was reduced by 77% (95% CI, 65%-85%) in vaccinated compared with unvaccinated girls from the 1997 cohort. Conclusions: In this largely HPV-naive population, we observed a substantial reduction in vaccine and nonvaccine types in vaccinated and unvaccinated girls following introduction of HPV vaccination.

HPV vaccination and risk of chronic fatigue syndrome/myalgic encephalomyelitis: A nationwide register-based study from Norway.

BACKGROUND: Vaccination has been suggested to be involved in the aetiology of chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). HPV vaccine was introduced in the Norwegian Childhood Immunisation Programme and offered 12year old girls from 2009. We studied the association between HPV vaccination and risk of CFS/ME and also assessed medical history in relation to both risk of CFS/ME and HPV vaccine uptake. METHODS: Individual data from national registries, including the Norwegian Population Registry, the Norwegian Patient Registry and the Norwegian Immunisation Registry were linked using the unique personal identification number. Yearly incidence rates of CFS/ME for 2009-2014 were calculated among the 824,133 boys and girls, aged 10-17 living in Norway during these 6years. A total of 176,453 girls born 1997-2002 were eligible for HPV vaccination and included in further analyses. Hazard ratios (HRs) of CFS/ME were estimated using Cox regression. Risk differences (RDs) of vaccine uptake were estimated with binomial regression. RESULTS: A similar yearly increase in incidence rate of CFS/ME was observed among girls and boys, IRR=1.15 (95% confidence interval (CI) 1.10-1.19) and 1.15 (95% CI 1.09-1.22), respectively. HPV vaccination was not associated with CFS/ME, HR=0.86 (95% CI 0.69-1.08) for the entire follow-up period and 0.96 (95% CI 0.64-1.43) for the first two years after vaccination. The risk of CFS/ME increased with increasing number of previous hospital contacts, HR=5.23 (95% CI 3.66-7.49) for 7 or more contacts as compared to no contacts. Girls with 7 or more hospital contacts were less likely to be vaccinated than girls with no previous hospital contacts, RD=-5.5% (95% CI -6.7% to -4.2%). CONCLUSIONS: No indication of increased risk of CFS/ME following HPV vaccination was observed among girls in the first 6 birth cohorts offered HPV vaccine through the national immunisation programme in Norway.

Do selective immunisation against tuberculosis and hepatitis B reach the targeted populations? A nationwide register-based study evaluating the recommendations in the Norwegian Childhood Immunisation Programme.

BACKGROUND: Selective immunisation is an alternative to universal vaccination if children at increased risk of disease can be identified. Within the Norwegian Childhood Immunisation Programme, BCG vaccine against tuberculosis and vaccine against hepatitis B virus (HBV) are offered only to children with parents from countries with high burden of the respective disease. We wanted to study whether this selective immunisation policy reaches the targeted groups. METHODS: The study population was identified through the Norwegian Central Population Registry and consisted of all children born in Norway 2007-2010 and residing in Norway until their second birthday, in total 240,484 children. Information on vaccinations from the Norwegian Immunisation Registry, and on parental country of birth from Statistics Norway, was linked to the population registry by personal identifiers. The coverage of BCG and HBV vaccine was compared with the coverage of vaccines in the universal programme. RESULTS: Among the study population, 16.1% and 15.9% belonged to the target groups for BCG and HBV vaccine, respectively. Among children in the BCG target group the BCG vaccine coverage was lower than the coverage of pertussis and measles vaccine (83.6% vs. 98.6% and 92.3%, respectively). Likewise, the HBV vaccine coverage was lower than the coverage of pertussis and measles vaccine in the HBV target group (90.0% vs. 98.6% and 92.3%, respectively). The coverage of the targeted vaccines was highest among children with parents from South Asia and Sub-Saharan Africa. The coverage of vaccines in the universal programme was similar in targeted and non-targeted groups. CONCLUSIONS: Children targeted by selective vaccination had lower coverage of the target vaccines than of vaccines in the universal programme, indicating that selective vaccination is challenging. Improved routines for identifying eligible children and delivering the target vaccines are needed. Universal vaccination of all children with these vaccines could be considered.

Human papillomavirus prevalence and type distribution in urine samples from Norwegian women aged 17 and 21 years: A nationwide cross-sectional study of three non-vaccinated birth cohorts.

BACKGROUND: The aim of the current study was to assess the HPV prevalence in unscreened and unvaccinated young women living in Norway, to provide important baseline data for early estimation of the impact of the HPV vaccination program. METHODS: A total of 13,129 self-sampled urine samples from two complete birth-cohorts of 17-year old women born in 1994 and 1996 and one third of a birth-cohort of 21-year old women born in 1990, were analysed for the presence of 37 HPV types using PCR and a DNA hybridization technique. RESULTS: In the two birth cohorts of 17-year old women, HPV was detected in 19.9% (95% CI 18.8-20.9) and 15.4% (95% CI 14.5-16.3), respectively. High-risk HPV types were detected in 11.2% (95% CI 10.3-12.0) and 7.6% (95% CI 6.9-8.2), respectively, while vaccine types were detected in 7.4% (95% CI 6.7-8.1) and 6.0% (95% CI 5.4-6.6), respectively. Among the 21-year old women HPV was detected in 45.4% (95% CI 42.9-47.8), whereas high-risk types were detected in 29.8% (95% CI 27.5-32.0). Vaccine types (HPV 6, 11, 16, 18) were detected in 16.2% (95% CI 14.4-18.1). CONCLUSION: This large population based study confirms that HPV testing in urine samples is easy and highly feasible for epidemiological studies and vaccine surveillance in young women. HPV was very common and a broad spectrum of HPV types was identified. Differences in HPV prevalence was seen both between age groups and between the two birth cohorts of 17-year old women.