Hepatitis B, meningococcal disease, pneumococcal disease
At both national and jurisdictional levels, notification and hospitalisation rates for acute hepatitis B were stable over the 2006–2007 period. This followed an increase in notification rates between 1993 and 2001 and a subsequent decline, while hospitalisations had been steady since 1999. The previously observed declines in notifications were most marked in young adults aged 15–29 years. This decline may be partly related to the lower rates of intravenous drug use since 2000, consistent with trends in hepatitis C virus notifications,4 but the adolescent catch-up programs that commenced from the late 1990s are likely to also play a role in maintaining low levels of disease in young adults. An even greater and more uniform impact can be expected from universal infant vaccination which commenced in 2000.
Substantial decreases in meningococcal notifications, hospitalisations and deaths were seen from 2003 to 2005, following the commencement in 2003 of the national routine vaccination program at 12 months of age and catch-up program for those aged <19 years. The decreases were seen in all target age groups (those aged <19 years in 2003), as well as in young adults outside the target age group, providing some evidence of continuing herd immunity. Those lows were sustained in the 2006–2007 review period. The reduction in notifications occurred in serogroup C disease, while notifications for serogroup B and other serogroups, mainly W135 and Y, remained relatively stable. The high burden of meningococcal disease in infants, particularly non-vaccine preventable serogroup B disease, emphasises the importance of early recognition and appropriate clinical management of disease and the need for a vaccine to reduce the significant morbidity and mortality. Several candidate serogroup B vaccines are under investigation.5 However, availability of a universal serogroup B vaccine appropriate for use in Australia is still some way off.
The 2006–2007 period covered in this report includes the second and third years of the implementation of funded 7-valent pneumococcal conjugate vaccine (7vPCV) for all Australian infants. This period saw an overall decrease of 40% in invasive pneumococcal disease (IPD) notifications and a 35% decrease in pneumococcal disease hospitalisations, compared to the 3 years immediately before the introduction of the program. Decreases were most marked in vaccinated age groups (72%–74% reductions), but also occurred in non-vaccinated age groups, with decreases of 20%–40% in adults. This has been seen in some other countries, and suggests herd immunity through the prevention of nasopharyngeal carriage. Increases in non-7vPCV serotypes were seen, in particular a 130% increase in serotype 19A. This is similar to observations in the USA, where there have been substantial increases in serotype 19A, but the overall IPD rate remains substantially lower in the general population than in the pre-vaccine era.6
In the elderly, the impact of funded 23-valent pneumococcal polysaccharide vaccine (23vPPV), also from 2005, is less clear. Decreases in IPD have been limited to 7vPCV serotypes, while non-7vPCV serotypes have increased, including those in the 23vPPV. However, increases in 23vPPV serotypes have been less than non-23vPPV serotypes, suggesting a possible impact of the 23vPPV. Estimates of 23vPPV effectiveness against IPD have been satisfactory in the otherwise healthy elderly,7 although lower than for the 7vPCV in children.
While Aboriginal and Torres Strait Islander people are not a separate focus of this report, IPD rates have been substantially higher, and non-vaccine serotypes more prevalent, in this population than in the non-Indigenous population.8 In the USA, significant serotype replacement has been observed among Alaskan Natives, a population with high incidence of invasive pneumococcal disease.9 Serotype replacement has not been documented in Australian Indigenous people so far, but should be closely monitored. New recently licensed 10- and 13-valent conjugate pneumococcal vaccines may make further contributions to pneumococcal disease control in the future in both Indigenous and non-Indigenous Australians.