No 18 - 2024

Invasive pneumococcal disease 2020-2023

• The occurrence of invasive pneumococcal disease was historically low during the COVID-19 pandemic in 2020 and 2021 (369 and 353 cases, respectively), but then increased in 2022 and 2023 (to 553 and 622 cases, respectively) and is now nearly in line with the number recorded in 2019 (639 cases).
• In the period from April 2020 to January 2023, a temporary vaccination programme was in place. The programme comprised a 23-valent pneumococcal vaccine (PPV23) administered to adults with an increased risk of running a serious clinical course of a pneumococcal infection.
• The most frequent serotypes in the 2020-2023 period were serotypes 8, 3, 22F, 9N and 24F. During the period, a significant decrease and stabilisation was registered in the number of cases caused by serotype 8, whereas serotype 3 increased in 2022 and 2023 and now causes more cases than before the COVID-19 pandemic.
• Two new conjugated pneumococcal vaccines have been approved for children and adults, Vaxneuvance (PCV15) and Prevenar 20, formerly Apexxnar (PCV20).

Pneumococci (Streptococcus pneumoniae) are found naturally in the nasopharynx without causing disease (known as carriage). This occurs more frequently in children than in adults. Additionally, pneumococci may cause pneumonia or acute otitis media, among others. If pneumococci are found in blood, cerebrospinal fluid or other normally sterile sites, the disease is coined invasive pneumococcal disease (IPD).

IPD is notifiable to the laboratory, and laboratory-based surveillance forms the basis for the Annual Report on Invasive Pneumococcal Disease 2020-2023, which contains a more detailed description of IPD in the period.

IPD occurrence in the 2020-2023 period

IPD occurrence has followed a steadily declining trend for all age groups since the introduction of pneumococcal vaccination in the childhood vaccination programme in 2007. The observed decline is partly owed to a direct effect in the youngest children (<2 years) and to an indirect effect in adults. The indirect effect is attributed to the fact that the vaccine used in the Danish childhood vaccination programme, a so-called conjugate vaccine, reduces carriage in vaccinated individuals; thereby decreasing the risk of infecting others.

In 2020 and 2021, the IPD occurrence was historically low, with 369 and 353 cases being recorded, Figure 1. This corresponds to decreases of 42% and 45%, respectively, compared with 2019, which registered the lowest number so far with 639 cases. The considerable decline in 2020 and 2021 is largely attributable to restrictions introduced due to the COVID-19 pandemic, which also reduced the transmission of other infectious diseases. The decline was most pronounced among the elderly, whereas this trend was not observed among children under 2 years of age. However, it should be noted that only 12-20 annual cases were recorded in the 2020-2023 period in this age group. In 2022 and 2023, the total number of cases increased once again to 553 and 622 cases, respectively, approaching the level recorded before the COVID-19 pandemic.

For the vast majority of IPD cases, pneumococci were detected in the blood, whereas a smaller proportion, 11% in 2020-2023, had pneumococci detected in cerebrospinal fluid.

Temporary vaccination programme

From April 2020 to January 2023, individuals aged 65 years and older and at-risk groups under 65 years were offered vaccination with the 23-valent pneumococcal vaccine, PPV23.

Among persons aged 65 years or more, coverage reached nearly 75%. A study based on Danish data has shown that in this target group from 15 June to 18 September, the vaccine was 58% (95 % CI: 21-78%) effective against IPD caused by the serotypes it covers.

In 2022, two new conjugated pneumococcal vaccines for individuals aged 18 years and older were approved for use in Denmark. Subsequently, both vaccines have also been approved for use in children from six weeks of age. The vaccines are a 15-valent vaccine (PCV15) and a 20-valent vaccine (PCV20).

Some vaccines are covered by conditional subsidies when used in specific groups. Please see the SSI website for guidance on the pneumococcal vaccination options.

Serotypes

Pneumococci are divided into serotypes of which there are more than 100. Among the samples for which the serotype was known, serotype 8 was the most commonly occurring in individuals with IPD during the 2013-2021 period, Figure 2. The highest incidence was recorded in 2017 and 2018, with 194 cases each year. In 2020, the number dropped drastically; in 2020-2023, it ranged from 73 to 83 cases. This trend may be related to the fact that the vaccine (PPV23), offered in the temporary vaccination programme for adults, covers serotype 8.

The occurrence of IPD caused by serotype 3 also declined in 2020 and 2021, but increased steeply in 2022 and 2023 and has now reached the highest number recorded in the 2000-2023 period. This development has occurred even though serotype 3 is covered by Prevenar 13, which was included in the Danish childhood vaccination programme in 2010, as well as by PPV23 and the two new vaccines PCV15 and PCV20.

In addition to serotype 3 and serotype 8, serotypes 22F, 9N and 24F were among the most frequent in the 2020-2023 period.

(F. K. Lomholt, P. Valentiner-Branth, T. Dalby, Department of Infectious Disease Epidemiology and Prevention, H-C. Slotved, K. Fuursted, Department of Bacteria, Parasites & Fungi, C. S. Jørgensen, Department of Microbiological Diagnostics and Virology)
1 May 2024