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Surveillance of seasonal respiratory illnesses

Updated: 11 June 2024

 

Background

The weekly Surveillance of seasonal respiratory illnesses report by Public Health Isle of Man presents epidemiological information on the activity of seasonal respiratory illnesses, on the Isle of Man.  Routine surveillance and monitoring of respiratory illnesses is crucial to assessing the burden of respiratory disease, and their impact on services.  Monitoring becomes especially important in the winter months (September to March) when the disease burden can be highest.  Data collected from this integrated surveillance system generates intelligence to provide a comprehensive and timely epidemiological picture of respiratory illness on the Isle of Man, which is essential for understanding transmission of infection, and supporting patient care, service planning, and policy decisions.

 

2023/24 Winter Season Summary

During the 2023/24 season, there was an expected increase in the weekly rate of GP consultations for acute respiratory infections (ARIs) during the winter months.  This seasonal increase was similar to that seen in previous years, however, the weekly rate did not go above the baseline threshold.  From this, we can infer that the 2023/24 winter was relatively mild for ARIs, compared to previous years.  The trend seen on the Isle of Man was comparable to that seen in England, with an increase during the same period which did not pass over the baseline threshold at any point in the season.

During the 2023/24 winter period, the out-of-hours GP service Manx Emergency Doctor Service (MEDS) experiences a significant change to its operating procedures.  As such, the summary here is relevant to data up to week 1 of 2024.  The data shows that the MEDS service experienced a similar trend compared to previous years, with a steady increase in weekly calls, followed by a larger increase in week 51.  This seasonal pattern was to be expected based on previous yearly data.

Data for hospital emergency department (ED) attendances for respiratory illnesses showed a similar, but slightly delayed pattern of increase over the winter months.  The 2021/22 winter season saw the highest peak in ED attendances for respiratory illnesses, reaching the high intensity epidemic threshold in weeks 51 and 52.  The 2023/24 saw several weekly increases in ED attendances that entered the medium intensity threshold; these came comparatively later in the season, most notably in weeks 5 and 7.  The data for this indicator suggests the 2023/24 season saw a lower, but more prolonged peak in ED attendances for respiratory illnesses.

The 2023/24 seasonal report introduced new data from the Manx Care Infection Prevention and Control team, based at Noble’s Hospital.  This data provided weekly number of positive test results for COVID-19, RSV, Influenza A, and Influenza B.  The data from this showed that the various Manx Care settings (detailed in the full report) saw successive waves of different respiratory illnesses.  There was firstly an increase and drop-off of RSV cases in those aged under 18.  This was later followed by a larger, more prolonged increase, and subsequent drop-off of Influenza A cases.  Whilst weekly number of COVID-19 cases remained relatively lower than RSV or Influenza A, the data suggests that COVID-19 activity fluctuated throughout the winter months.

Due to the small number of deaths that are registered on the Isle of Man each week, and the delays that occur with the registering of deaths, trends in mortality data should be interpreted with caution.  Mortality data showed that deaths from all causes remained within two standard deviations of the 10-year weekly average throughout the 2023/24 season, apart from in week 2.  This suggests that there were no large increases in weekly deaths during the winter period.

As of 31 March 2024, total influenza vaccine uptake was 41.56% of those eligible.  The highest uptake was seen in those aged 65 and over, at 68.6%, whilst the lowest uptake was seen in those aged 50 – 64, at 21.2%.  When compared to the 2022/23 winter season, influenza vaccine uptake was lower in every eligibility group, with the most notable decrease being in those aged 50 – 64 (41.0% in 2022/23 vs 21.2% in 2023/24).  Figure 1 shows that, with the exception of the 50 – 64 age group, the uptake rate of influenza vaccines was similar to the 2022/23 winter season.

Figure 1: Influenza vaccine uptake for the 2023/24 and 2022/23 winter seasons, by vaccine cohort.  Note: monthly vaccine uptake defined as the cohort uptake at the last day of the corresponding month.

 

Regarding COVID-19 vaccination, total uptake, as of the final winter surveillance report, was 69.05% of those eligible.  The highest uptake was in those aged 65 and over at 87.4%, whilst the lowest uptake was in those aged 20 – 49, at 26.3%. Comparisons between this season and the 2022/23 season should not be made due to the differing eligibility criteria for the COVID-19 vaccines.

The Surveillance of seasonal respiratory illnesses report by Public Health Isle of Man includes data from several other publications from the United Kingdom Health Security Agency (UKHSA), European Centre for Disease Control (ECDC), and the World Health Organisation (WHO).

Regarding trends seen in the United Kingdom this winter, data from the UKHSA shows that England saw two ‘waves’ of confirmed COVID-19 episodes during the 2023/24 winter period.  The first wave peaked in week 40, and the second peaked at around week 52; this is shown in Figure 2.  Although the data presented in the UKHSA report is daily cases, this second peak in COVID-19 episodes approximately mirrors the increase in weekly COVID-19 cases seen via the Isle of Man’s Infection Prevention and Control data, albeit with a time-delay in Isle of Man data, which may be expected due to transmission patterns.

 

Figure 2: Confirmed COVID-19 episodes tested under Pillar 1, based on sample date with overall 7-day rolling average PCR positivity for Pillar 1 (%).1

 

Similarly, data for England shows that there was a large increase of Influenza positive samples beginning in week 49, which peaked around week 4; this is shown in Figure 3.  This, again, was approximately mirrored on the Isle of Man, however the Island saw a flatter and more prolonged peak in Influenza cases.  It should be noted that the majority of influenza cases in the UK were Influenza A cases, as was seen on the Isle of Man.

 

Figure 3: Respiratory DataMart samples positive for influenza by type and subtype, England.1

 

RSV activity in England saw a large increase and peak in week 48; shown in Figure 4.  This peak in RSV activity was similar in timing to that seen on the Isle of Man, which peaked in week 46.

 

Figure 4: Respiratory DataMart weekly positivity (%) for RSV by year, England.1

 

Data from the WHO shows that, across all monitored regions during the 2023/24 winter period, there was a large increase in Influenza A and B detections during December 2023.  This activity increased around the beginning of January and decreased to the end of the winter period, as shown in Figure 5.  This increase in influenza detections came at a similar time to the increase in the 2022/23 winter period, however, there were a larger proportion of Influenza B detections in 2023/24.  The activity seen in 2023/24 was also slightly lower at its peak than 2022/23, but had a more prolonged peak period.

 

Figure 5: Number of specimens positive for influenza by subtype globally.2

 

Data for global COVID-19 activity showed that, in the 2023/24 winter period, the majority of COVID-19 cases were reported in the four weeks commencing 11 December 2023.  The large majority of these cases were from the European region.  The highest number of COVID-19 deaths were also reported during this four-week period.  When compared to the 2022/23 winter period, the number of COVID-19 cases was vastly smaller in 2023/24; these data are shown in Figure 6.  Whilst this may demonstrate reduced COVID-19 activity across this time period, it should be noted that reported cases do not accurately represent infection rates due to the reduction in testing and reporting globally.

 

Figure 6: COVID-19 cases and global deaths by 28-day intervals reported by WHO Region, as of 31 March 2024 (A); 18 September 2023 to 31 March 2024 (B).3

 

Information presented here is based on the ECDC variant classification, and data on COVID-19 variants in the UK.  For the duration of the 2023/24 winter period, there have been no Variants of Concern (VOC), according to the ECDC definitions.  There have been a number of variants added, and de-escalated, to both the Variants of interest (VOI) and Variants under monitoring (VUM) lists during the 2023/24 winter period.  The 2023/24 winter period saw large changes in the prevalence of COVID-19 variants circulating in the UK.  The majority of variants at the beginning of the data period were XBB.1 and EG.5.1; this dominant prevalence was replaced by the JN.1 variant (and sub variants) over the course of December and January, and remains the dominant variant as of the latest update.4  These changes are shown in further detail in Figure 7.

 

Figure 7: Prevalence of Pangolin lineages in the UK sequence data with a specimen data from week beginning 9 October 2023 to week beginning 11 March 2024, as of 25 March 2024.

 

References

  1. UKHSA. National flu and COVID-19 surveillance reports: 2023 to 2024 season. Accessed April 30, 2024. https://www.gov.uk/government/statistics/national-flu-and-covid-19-surveillance-reports-2023-to-2024-season

  2. Global Influenza Programme. Accessed April 30, 2024. https://www.who.int/teams/global-influenza-programme/surveillance-and-monitoring/influenza-updates/current-influenza-update

  3. COVID-19 epidemiological update – 12 April 2024. Accessed April 30, 2024. https://www.who.int/publications/m/item/covid-19-epidemiological-update-edition-166

  4. SARS-CoV-2 genome sequence prevalence and growth rate update: 27 March 2024 - GOV.UK. Accessed April 30, 2024. https://www.gov.uk/government/publications/sars-cov-2-genome-sequence-prevalence-and-growth-rate/sars-cov-2-genome-sequence-prevalence-and-growth-rate-update-27-march-2024