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Impact of Universal Infant Immunization with Pneumococcal (Streptococcus pneumonia) Conjugate Vaccines in Alaska

1 August 2008


Purpose: To describe and compare the impact of universal infant immunization with 7-valent pneumococcal conjugate vaccine (PCV7) on invasive Streptococcus pneumoniae infection, nasopharyngeal carriage, and antibiotic resistance in Alaskan Native and non-Native children and adults.

Methods: The medical literature concerning the epidemiology of invasive pneumococcal disease (IPD) and the effects of pneumococcal conjugate vaccine on the incidence, nasopharyngeal carriage, and antibiotic resistance of S pneumoniae was reviewed with special emphasis on the effects in the Alaska Native population.

Results: Alaska Native children experienced the highest incidence of IPD in the United States. The greatest difference in IPD was among children younger than 2 years for whom the annualized rate in Alaskan Native children (450/100,000 per year) was 3 times higher than for non-Native Alaskan children younger than 2 years who had rates similar to the overall US population.

In the first 3 years after beginning routine vaccination with PCV7 (2001-2003), overall IPD decreased 67 percent in Alaska Native children younger than 2 years (from 403.2 per 100,000 in 1995-2000 to 134.3 per 100,000 per year in 2001-2003, P < .001). However, between 2001-2003 and 2004-2006, there was an 82 percent increase in invasive disease in Alaska Native children younger than 2 years to 244.6/100 000 (P = .02). Since 2004, the IPD rate caused by nonvaccine serotypes has increased 140 percent compared with the prevaccine period (from 95.1 per 100,000 in 1995-2000 to 228.6 in 2004-2006, P = .001). During the same period, there was a 96 percent decrease in heptavalent vaccine serotype disease in Alaskan Native children. Serotype 19A accounted for 28.3 percent of invasive pneumococcal disease among Alaska children younger than 2 years during 2004-2006. There was no significant increase in nonvaccine disease in non–Native Alaska children younger than 2 years between 2001-2003 and 2004-2006.

During 1998–2004, the overall proportion of Alaska Native children < 5 years of age colonized with S. pneumoniae remained stable (59 percent at baseline and 61 percent in 2004), but there was an upward trend among adults >18 years of age (13 percent at baseline and 26 percent in 2004). This trend of increased nasopharyngeal carriage of S. pneumoniae in adults was observed among adults in all age classes. Among children < 5 years of age who were colonized with S.>pneumoniae, the proportion with PCV7-type pneumococcal carriage decreased from 55 percent at baseline to 5 percent in 2004. Among adults colonized with S. pneumoniae, carriage of PCV7-type pneumococci decreased from 28 percent to 5 percent over this same period. Accordingly, because PCV7-type colonization decreased but overall colonization did not, there has been a marked increase in the proportion of adults with colonization due to non–PCV7-type pneumococci.

After beginning routine vaccination with PCV7, disease caused by penicillin-nonsusceptible strains among rural Alaska Natives decreased 81 percent (95% CI, 80-82%) among children under two years of age, and 49 percent among persons 65 years of age or older. Rates of resistant disease caused by vaccine serotypes fell 87 percent. Introduction of PCV7 into the routine infant immunization schedule in a community with a high prevalence of antimicrobial-resistant pneumococci (Anchorage, Alaska) appears to reduce transmission of PCV7 vaccine serotypes and cotrimoxazole nonsusceptible pneumococci but has no impact on overall carriage of pneumococci or carriage of penicillin nonsusceptible pneumococci.

In 2000, 93.7 percent of Alaskan homes had complete sanitation services (potable drinking water and safe wastewater disposal), which ranked Alaska last among US states. The percentage of homes with in-home water service in many parts of rural Alaska is significantly lower. Higher respiratory and skin infection rates were associated with a lack of in-home water service. Regions with a lower proportion of home water services had significantly higher hospitalization rates for pneumonia and influenza (RR = 2.5), skin or soft tissue infection (RR = 1.9), and respiratory syncytial virus (RR = 3.4 among those younger than 5 years) than did higher-service regions.

Conclusion: The PCV7 vaccine has nearly eliminated IPD caused by vaccine serotypes in Alaskan children younger than 5 years. However, this success has been diminished by a significant increase in non-PCV7 serotype IPD in Alaska Native children. Vaccination does not change the overall risk of pneumococcal carriage. However, it does reduce the acquisition of vaccine serotypes and increases the acquisition of nonvaccine serotypes. Although there has been an overall decline in the proportion of invasive isolates nonsusceptible to penicillin, increases in the rates of penicillin-nonsusceptible IPD caused by nonvaccine serotypes and by vaccine-related strains of S. pneumoniae (particularly 19A) have been noted.

The increase in replacement IPD also highlights the need for continued surveillance and other epidemiological investigations to monitor the effects of pneumococcal vaccines. Under antibody selective pressure, pneumococci can be expected to quickly evolve to circumvent vaccines that contain a limited number of serotypes. The only long-term solution to the problem is the development of a vaccine containing one or several protective protein antigens from pneumococcus.

In rural Alaska, basic improvements in housing, access to treated running water, instillation of sewage disposal and treatment facilities and improved economic opportunity would have far-reaching beneficial health effects. Although PCV7 has eliminated the disparity in vaccine-type IPD, health disparities among Alaska Natives are likely to continue until those disparities in living conditions are also eliminated.


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