1 Summary

• From 01 January 2024 to 31 December, 3612 clinically suspected pertussis cases have been notified to the Public Health Agency.
• Of those notified during 2024 to 31 December, 3061 were confirmed.

2 Background

Pertussis (also known as “whooping cough”) is a highly contagious but vaccine preventable bacterial respiratory disease that is usually caused by Bordetella pertussis. It is normally characterised by a “whooping” cough, cold and fever. For more information about pertussis, please visit NI Direct | Pertussis. Pertussis typically follows a cyclical pattern with epidemics occurring every three to five years. For more information about previous years’ reports, please visit PHA | Annual VPD Reports.

A vaccine against pertussis, which also provides protection against diphtheria, tetanus, polio, Haemophilus influenzae type b (Hib) and hepatitis B (DTap/IPV/Hib/HepB vaccine) is included in the Northern Ireland childhood vaccination schedule at age two, three, and four months. A further booster against pertussis (also protecting against diphtheria, tetanus and polio) is provided three years after the primary course and before school entry. Vaccination against pertussis can also be offered prenatally (to pregnant women) ideally from 16 weeks up to 32 weeks pregnant.

For more information on the childhood immunisation programme, please visit NI Direct | Childhood immunisation programme and for further information on pertussis vaccination for pregnant women, please visit NI Direct | Whooping cough vaccination for pregnant women.

Details of case definitions and methods are at the end of this document. Data were correct at 31 December 2024.

3 Pertussis notifications, 2019-2024

The number of notified clinically suspected pertussis cases from the start of 2019 until the report date (31 December) are shown (Table 3.1).

Please note: in the table above data for 2024 is up to 31 December

3.1 Trends

Pertussis notifications in Northern Ireland increased between January 2024 and May 2024 (Figure 3.1). The noted increases are partly attributable to increased awareness. The number of cases reported in May 2024 were the highest during any month in 2024. There have been 3061 confirmed pertussis cases reported in 2024 to date. The highest number of confirmed cases have been reported in those aged 5-9 years (590), 10-14 years (711) and 25 years and older (972). PHA received updated serological lab reports resulting in an artefactual rise in notifications in the following weeks; week commencing 15 July 2024 (n=86), week commencing 26 August 2024 (n=6), week commencing 02 September 2024 (n=71) and week commencing 30 September 2024 (n=49). These results relate to tests during the period January to August 2024. Excluding the historic notifications, the number of notifications reported per month has continued to decrease since peaking in May 2024. The decrease in notifications followed a change in testing guidance and updated case definition which includes epidemiological confirmation of cases (details of case definitions are at the end of this document). The rate of confirmed cases per 100,000 population increased between January 2024 and May 2024. The highest rate of confirmed cases were observed in those aged under 1 year (176.2 cases per 100,000) and 10-14 years (180.2 cases per 100,000) in May 2024 (Figure 3.2).

The supplementary table below shows counts of pertussis notifications recorded by month and by age group.

Figure 3.1: Incidence of pertussis notifications, by month of notification, all ages, 2019 - 2024.

Figure 3.2: Rate of confirmed pertussis cases, by month of notification, by age group, 2024.

4 Discussion

There have been 3061 confirmed pertussis cases during 2024. There was an increase in notifications of clinically suspected and confirmed pertussis in 2024. Similar increases have been reported in multiple countries across Europe. The number of pertussis cases reported during 2020 to 2023 had been particularly low, a secondary impact of interventions to control the spread of COVID-19. To date in 2024, the highest number of confirmed cases have been reported in those aged 5-9 years, 10-14 years and 25 years and older. The highest rates of confirmed pertussis have been reported in those aged under 15 years of age.

Pertussis vaccine coverage has reduced in Northern Ireland during recent years; NI PHA | Vaccination coverage. Increasing coverage of pertussis vaccination, both prenatal and in childhood, is crucial to ensure widespread protection and keep cases of pertussis low.

5 Methods

Pertussis notifications are reported by clinicians to the Public Health Agency and were extracted from the case management database. Pertussis is notifiable in Northern Ireland under the Public Health Act (1967) Northern Ireland.

Cases are presented by the date that they were recorded on the PHA database. Notified cases will be removed from future reports if PHA is notified that clinical investigations later result in an alternative diagnosis. Updated lab results will be added to future reports based on the date they were notified to the PHA. Numbers may therefore change from previous reports.

Data were processed using R.

6 Supplementary Tables

Table 6.1: Count of pertussis notifications by case category and month of notification, 2019-2024.

Table 6.2: Count of confirmed pertussis cases by age group and month of notification, 2024.