Quadrivalent Human Papillomavirus Vaccine Effectiveness
Quadrivalent Human Papillomavirus Vaccine Effectiveness
The population cohort included 2 209 263 girls and women aged 10 to 44 years living in Sweden between 2006 and 2010, contributing 9 640 542 person-years; 33 178 participants had GW during follow-up. More than 5% of the study population received at least one dose of the qHPV vaccine, with 124 000 girls and women vaccinated, 90% of whom were in the subsidized target group. Of all vaccinated girls and women, 78.5% were fully vaccinated. The highest vaccination coverage was among those aged 18 to 19 years (vaccination coverage = 31.9%) and 13 to 17 years (vaccination coverage = 24.7%) (Table 1). Girls and women who had at least one university-educated parent were approximately 15 times more likely to be vaccinated before age 20 years than girls and women whose parents did not complete high school (RRR = 15.45, 95% CI = 14.65 to 16.30) ( Table 2 ). Maternal university education level was more strongly associated with vaccination status outcome than paternal university education level (RRR = 8.58, 95% CI = 8.32 to 8.85; vs RRR = 4.31, 95% CI = 4.22 to 4.41). Similar patterns for associations with education were seen for those vaccinated at age 20 years and older ( Table 2 ).
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Table 1.
Vaccination status, genital warts cases, and parental education level among all girls and women in Sweden aged 10 to 44 years between January 2006 and December 2010
To assess whether there was a self-selection bias among those who were vaccinated, we compared the rate of GW before commercial availability of qHPV with rate of GW at the end of follow-up in the unvaccinated population. No statistically significant difference in the rates were found in the age category with highest vaccine coverage (aged 14–19 years) (IRR = 1.00, 95% CI = 0.98 to 1.02). Among women aged 20 years or older, the GW rates declined over time in the unvaccinated population (IRR = 0.96, 95% CI = 0.95 to 0.97), suggesting a self-selection bias in which individuals at a higher risk for GW were more likely to seek vaccination (data not shown).
Vaccine effectiveness was 76% (95% CI = 73% to 79%) among those who received three doses of the vaccine with their first dose before age 20 years. Vaccine effectiveness was highest in girls vaccinated before age 14 years (effectiveness = 93%, 95% CI = 73% to 98%). Effectiveness was 80% (95% CI = 75% to 83%) for girls vaccinated at ages 14 to 16 years, 71% (95% CI = 65% to 76%) at ages 17 to 19 years, and 48% (95% CI = 22% to 65%) for women vaccinated at ages 20 to 22 years. No effectiveness was measureable in fully vaccinated women who received their first dose when they were aged older than 22 years (Table 3).
When comparing the IR predicted under the assumption of complete vaccination with that predicted under no vaccination, the greatest reduction in IR was for complete vaccination among the earliest age group considered (10–13 years), with a maximum reduction in IR of 332.35 per 100 000. The maximum reduction in IR decreased with each subsequent older age category and was nonexistent for the group aged 27 years or older (Table 3).
Results
The population cohort included 2 209 263 girls and women aged 10 to 44 years living in Sweden between 2006 and 2010, contributing 9 640 542 person-years; 33 178 participants had GW during follow-up. More than 5% of the study population received at least one dose of the qHPV vaccine, with 124 000 girls and women vaccinated, 90% of whom were in the subsidized target group. Of all vaccinated girls and women, 78.5% were fully vaccinated. The highest vaccination coverage was among those aged 18 to 19 years (vaccination coverage = 31.9%) and 13 to 17 years (vaccination coverage = 24.7%) (Table 1). Girls and women who had at least one university-educated parent were approximately 15 times more likely to be vaccinated before age 20 years than girls and women whose parents did not complete high school (RRR = 15.45, 95% CI = 14.65 to 16.30) ( Table 2 ). Maternal university education level was more strongly associated with vaccination status outcome than paternal university education level (RRR = 8.58, 95% CI = 8.32 to 8.85; vs RRR = 4.31, 95% CI = 4.22 to 4.41). Similar patterns for associations with education were seen for those vaccinated at age 20 years and older ( Table 2 ).
(Enlarge Image)
Table 1.
Vaccination status, genital warts cases, and parental education level among all girls and women in Sweden aged 10 to 44 years between January 2006 and December 2010
To assess whether there was a self-selection bias among those who were vaccinated, we compared the rate of GW before commercial availability of qHPV with rate of GW at the end of follow-up in the unvaccinated population. No statistically significant difference in the rates were found in the age category with highest vaccine coverage (aged 14–19 years) (IRR = 1.00, 95% CI = 0.98 to 1.02). Among women aged 20 years or older, the GW rates declined over time in the unvaccinated population (IRR = 0.96, 95% CI = 0.95 to 0.97), suggesting a self-selection bias in which individuals at a higher risk for GW were more likely to seek vaccination (data not shown).
Vaccine Effectiveness
Vaccine effectiveness was 76% (95% CI = 73% to 79%) among those who received three doses of the vaccine with their first dose before age 20 years. Vaccine effectiveness was highest in girls vaccinated before age 14 years (effectiveness = 93%, 95% CI = 73% to 98%). Effectiveness was 80% (95% CI = 75% to 83%) for girls vaccinated at ages 14 to 16 years, 71% (95% CI = 65% to 76%) at ages 17 to 19 years, and 48% (95% CI = 22% to 65%) for women vaccinated at ages 20 to 22 years. No effectiveness was measureable in fully vaccinated women who received their first dose when they were aged older than 22 years (Table 3).
When comparing the IR predicted under the assumption of complete vaccination with that predicted under no vaccination, the greatest reduction in IR was for complete vaccination among the earliest age group considered (10–13 years), with a maximum reduction in IR of 332.35 per 100 000. The maximum reduction in IR decreased with each subsequent older age category and was nonexistent for the group aged 27 years or older (Table 3).
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