Invasive pneumococcal disease 2018-2019

Annual report: Invasive pneumococcal disease and coverage of pneumococcal vaccination in the childhood vaccination programme 2018 and 2019

Invasive pneumococcal disease (IPD) is defined as a disease episode for which pneumococci (Streptococcus pneumoniae) have been detected in cerebrospinal fluid, blood or another normally sterile sampling material. For more information about IPD and pneumococcal vaccination, please see the SSI website. Since October 2007, when pneumococcal vaccination was introduced into the childhood vaccination programme, laboratories have had a legal obligation to notify findings of invasive pneumococci and to submit bacterial isolates to the SSI, among others for serotype determination. This annual report focuses on isolate-based monitoring and is based on data from submitted isolates and from the Danish Microbiology Database, MiBa.

Occurrence of invasive pneumococcal disease

In 2018 and 2019, a total of 799 and 639 IPD cases, respectively, were detected in Denmark. This corresponds to incidences of 13.8 and 11.0 per 100,000. Thus, 2019 became the year with the lowest number of cases recorded since monitoring was introduced in 2007. For comparison, the incidence prior to the introduction of the vaccine was approx. 20 per 100,000.

In 2018, 713 cases were detected in blood, 75 cases in spinal fluid (meningitis) and the remaining 11 isolates were detected in other sterile sampling material. For 2019, the corresponding figures were 582, 41 and 16. These proportions were in line with those recorded in previous years.

IPD is primarily seen among very young children and elderly people; and, in general, the occurrence of IPD has followed a decreasing trend since the introduction of the PCV vaccine. The PCV vaccine, in particular, has had a substantial effect on the occurrence of PCV among very young children, as the incidence among the <2-year-olds decreased from 55 per 100,000 in the period 2000-2007 to 10 and 19 in 2018 and 2019, respectively. The effect is also observed in other age groups, and among elderly people, aged 65 years or more, the incidence thus declined from 66 per 100,000 in the 2000-2007 period to 47 and 36 in 2018 and 2019, respectively. The PCV vaccine presumably reduces the number of carriers of vaccine-type pneumococci among vaccinated children, thereby reducing the risk of further transmission, a phenomenon known as herd immunity. In 2019, the incidence increased slightly compared with 2018 among young children <2 years of age, but the changes in real figures between the two years are very limited.

Figure 1 presents the occurrence as number per age group, and Figure 2 shows the incidence per age group as IPD per 100,000 per year.

More than 95 different types of pneumococci are known, and their propensity to cause infections and serious infections in humans vary. The occurrence of the, initially seven, then thirteen, serotypes comprised by the vaccine, has declined considerably since the introduction of the vaccine. Even so, the occurrence of non-vaccine serotypes has increased in recent years as has been the case in other countries. In particular, serotype 8 has become dominant with 26% of all IPD in 2019. In 2019, serotype 3, which is comprised by the PCV-13 vaccine, was the second-most frequent cause of IPD, accounting for 11% of the overall number of cases. However, serotype 3 is primarily seen among elderly people. It is extremely rare among children; and when seen in children, these children are typically unvaccinated. Worldwide, efforts are being made to develop vaccines that cover more, or other, types than those currently covered. Figure 3 and Figure 4 show the occurrence of vaccine serotypes among IPD cases for all ages and for children aged 0-4 years, respectively.

Vaccination coverage

The coverage of PCV in the childhood vaccination programme has increased gradually since its introduction in 2007. For birth cohorts 2009-2018, the coverage was 86-97% for the first PCV, 87-97% for the second PCV and 88-92% for the third PCV, Table 1. The geographical differences in vaccination coverage are modest. With respect to the third PCV for the 2018 birth cohort, coverage ranged from 90% in the City of Copenhagen to 94% in West Jutland, whereas the 2017 birth cohort recorded a 94% coverage in the City of Copenhagen and 98% on Bornholm, see the vaccination coverage data in the Figures and Graphs section.