Contents

15 Pneumococcal disease

15.3 Epidemiology

15.3.1 New Zealand epidemiology

Pneumococcal disease occurs throughout the year, but is more common in the autumn and winter months.2 The risk of disease is highest in infants,3, 4 especially Māori and Pacific infants, and in elderly people.

Invasive isolates from cases of IPD are serogrouped and serotyped at the Institute of Environmental Science and Research (ESR). IPD became a notifiable disease in October 2008 with direct laboratory notification to public health units, which, along with ESR laboratory serotyping, allows accurate national surveillance of all IPD in New Zealand. Detailed surveillance information can be found on the ESR Public Health Surveillance website (www.surv.esr.cri.nz/surveillance/IPD.php).

ESR laboratory-based surveillance provides an estimate of the coverage of IPD isolates by available vaccine serotypes. During the two years (2006–2007) prior to the introduction of PCV7, 82 percent of cases in children aged under 5 years were due to serotypes contained in PCV7, 84 percent to PCV10 serotypes and 94 percent to PCV13 serotypes.5 The relative importance of serotypes varies by age group and year by year. See Table 15.1 for a summary of serotypes contained in the pneumococcal vaccines.

Table 15.1: Summary of pneumococcal vaccine serotype content

Vaccine Serotypes
PCV13 Includes:
  • serotypes 4, 6B, 9V, 14, 18C, 19F, 23F (previously contained in PCV7)
  • plus serotypes 1, 5, 7F (previously contained in PCV10)
  • ​plus serotypes 3, 6A, 19A.
23PPV Includes:
  • the serotypes contained in PCV13 (except for 6A)
  • ​plus serotypes 2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20, 22F, 33F.

The 7-valent pneumococcal conjugate vaccine (PCV7, Prevenar 7) and the 23-valent pneumococcal polysaccharide vaccine (23PPV, Pneumovax 23) were introduced in 2006 for high-risk individuals. PCV7 became part of the Schedule in June 2008, and in July 2011 was replaced by the 10-valent pneumococcal conjugate vaccine (PCV10, Synflorix). The 13-valent pneumococcal conjugate vaccine (PCV13, Prevenar 13) replaced PCV7 for high-risk individuals in July 2011 and replaced PCV10 for all children in July 2014.

The effect of PCV7 on IPD has been well-documented internationally, with significant reductions in vaccinated children and indirect effects on unvaccinated individuals (ie, a herd immunity effect; see the herd immunity discussion below).

15.3.2 New Zealand epidemiology since the introduction of PCVTop

There have been dramatic reductions in the incidence of IPD in the vaccine-eligible age groups in New Zealand since the introduction of PCV7. The rate of IPD in New Zealand children aged under 2 years has decreased by 80 percent since the introduction of PCV7: from an average annual rate of 100.8 per 100,000 for 2004–2007 to 20.4 per 100,000 in 2013.4 The impact on IPD caused by PCV7 serotypes in this age group is even greater, with a 98 percent decrease from an average rate of 83.1 per 100,000 in 2006/07 to 1.6 per 100,000 in 2012 (note that the 2012 rate was calculated based on two cases only).6

There was one case caused by a PCV7 serotype in a child aged under 2 years in 2013.7 The rate of IPD has also significantly decreased in children aged 2 to 4 years, for all-cause IPD and IPD caused by PCV7 serotypes.

Figure 15.1 and Table 15.2 show the rates of IPD by age group and vaccine serotype since the introduction of PCV7. See also the herd immunity section below for the effect on IPD in those age groups who were not eligible for funded vaccine.

Notification rates for IPD since 2011 (with the change to PCV10)

The IPD rate for children aged under 2 years for 2013 (20.4 per 100,000 population, 25 cases) was a significant decrease from the 2012 rate (30.8 per 100,000 population, 44 cases). During 2013 the highest rates were for individuals aged 65 years and older (30.8 per 100,000 population, 188 cases) and children aged under 2 years. The notification rate for all ages for 2013 (10.9 per 100,000 population, 482 cases) was a non-significant decrease from the 2012 rate (11.1 per 100,000 population, 489 cases).7

Disease caused by PCV7 and PCV10 vaccine serotypes

PCV7 serotypes accounted for just 20 percent of IPD cases across all age groups in 2013, with only one case due to a PCV7 type in children aged under 5 years.7 The additional three serotypes in PCV10 accounted for further 16 percent of IPD cases. Cases of the PCV10 type 7F increased 86 percent between 2012 and 2013 (37 to 69 cases), with the result that 7F was the second most common serotype among IPD cases in 2013. However, the increase in type 7F cases in 2013 occurred wholly in those aged 5 years and older and were therefore not eligible to receive PCV10.

Disease caused by non-PCV10 vaccine serotypes

Serotype 19A was the most common type among IPD cases in 2013, although cases due to 19A actually decreased from 80 in 2012 to 75 in 2013.7 The second most common non-PCV10 serotype in 2013 was type 22F. However, there was little change in cases of 22F disease between 2012 and 2013 (40 to 41 cases).

Figure 15.1: Rates per 100,000 of invasive pneumococcal disease by vaccine coverage, age group and year, 2006–2012

Figure 15.1: Rates per 100,000 of invasive pneumococcal disease by vaccine coverage, age group and year, 2006–2012

Notes: PCV7 was introduced in 2008 and PCV10 in 2011. IPD became a notifiable disease in 2008.

Source: Institute of Environmental Science and Research

Table 15.2: Decrease in rates of culture-positive invasive pneumococcal disease due to PCV7 serotypes between 2006–2007 and 2012, by age group

Age group Rate of IPD due to PCV7 serotypes per 100,000 population Percentage reduction between time periods
  2006–2007 2012  
<2 years 83.1 1.6* 98
<5 years 43.2 1.3* 98
5–64 years 3.6 1.9 46
≥65 years 22.2 9.5 57
All ages 8.6 2.9 66
* Rate should be interpreted with caution as it relates to fewer than five children.

Source: Institute of Environmental Science and Research

Impact of vaccination on non-invasive pneumococcal disease

The impact of pneumococcal conjugate vaccination on the large burden of non-invasive pneumococcal disease has been clearly demonstrated internationally in countries that have introduced these vaccines, particularly through reductions in hospitalisations due to pneumonia.8, 9 Other impacts, such as on acute otitis media, are less clear and more difficult to measure accurately.10

In New Zealand there is some evidence from South Auckland that the introduction of PCV7 has been associated with fewer admissions for pneumonia in young children.11 However, there are ethnic disparities, with impacts more apparent for Pacific infants and less so for Māori in pneumonia hospitalisation. This is in contrast to IPD data, where there has been a reduction in disease in Māori children aged under 2 years but not in Pacific children (Māori: decrease from 86.6 per 100,000 in 2009 to 43.3 per 100,000 in 2012; Pacific: increase from 64.0 per 100,000 in 2009 to 83.0 per 100,000 in 2012).6, 12

Herd immunity

There is good evidence for the indirect effects of infant PCV immunisation on pneumococcal disease due to vaccine serotypes in the non-vaccinated population, especially in adults aged 65 years and older. This includes data showing reductions in the rates of IPD due to PCV7 serotypes in non-vaccinated groups in New Zealand,6 the US (for both adult pneumonia and IPD in adults),13–15 England and Wales,16 the Netherlands,17 Norway18 and Denmark.19 These herd effects are likely to be due to decreased nasopharyngeal carriage of vaccine types in immunised children resulting in reduced transmission to unimmunised children and adults. Although most of the data available is for the indirect effect on IPD, there is also evidence of an all-age effect on non-bacteraemic pneumonia.20 Early data from Norway21 and Canada22 indicates further decreases in vaccine-type IPD in non-vaccinated populations (aged 5 years and older) after PCV13 replaced PCV7 on the infant immunisation schedule.

The herd effects of adding PCV7 to the New Zealand schedule in 2008 were evident by 2012, with significant reductions in IPD due to PCV7 types in all age groups, not just those that were eligible for routine infant immunisation (Figure 15.1 and Table 15.2).6 The rate of IPD due to PCV7 serotypes in the 65 years and older age group decreased 57 percent, from an average of 22.2 per 100,000 population in 2006–2007 to 9.5 per 100,000 in 2012, while in the 5–64 years age group there was a 46 percent decrease over the same time period (3.6 to 1.9 per 100,000).

Antimicrobial resistance

As in other countries, there has been concern at the increase in the prevalence of antimicrobial resistance in S. pneumoniae in New Zealand.6 Introduction of pneumococcal conjugate vaccination has reduced the circulation of resistant pneumococcal serotypes elsewhere.23 In New Zealand, trends for S. pneumoniae resistance to betalactams (penicillin and cefotaxime) and multi-resistance over the last 10 years have varied; the 2012 rate of penicillin resistance (meningitis interpretation) of 17.2 percent was within the range of rates recorded for other years during the last decade (14–22 percent).

In 2012 ESR surveillance shows that PCV7 serotypes now account for a smaller proportion (44 percent) of the penicillin-resistant isolates than previous years, and the non-PCV10 type 19A, accounts for a larger proportion (39 percent). However, this increase in the proportion of penicillin-resistant isolates that are type 19A is due to 19A causing a greater proportion of IPD cases rather than penicillin resistance becoming more common among this serotype.6