Integrated surveillance of respiratory infections in 2024/2025 - consolidated report
Integrated surveillance of respiratory infections in 2024/25 – consolidated report
Summary of the respiratory season 2024/25
In the 2024/25 season, the overall surveillance of respiratory infections included not only the three well-known viruses – influenza, RSV, and SARS-CoV-2 – but also the bacterial infection Mycoplasma pneumoniae. This is due to the fact that M. pneumoniae continued to circulate at a high level in the 2024/25 season.
Already during the summer and autumn of 2024, an elevated incidence of both SARS-CoV-2 and M. pneumoniae was observed. At the end of November, the number of cases with influenza and RSV also began to rise – a pattern that followed the seasonal course known from before the COVID-19 pandemic. This led to a peak in the burden of infections, hospitalizations, and SARI hospitalizations (hospitalizations with severe respiratory infection) in February 2025, figure 1.
- Influenza: The influenza season was intense, where from the beginning of 2025 onwards, the influenza virus was the most dominant respiratory infection – both in terms of number of infected and hospitalized patients. For several weeks, both the number of cases and hospitalizations were at a high level.
- Covid-19: The season was milder than previous periods, as the number of cases and hospitalizations remained at a medium level throughout 2024, and then fell to a low level in 2025.
- RSV: The number of RSV cases and related hospitalizations reached a high level in some weeks. Overall, the RSV season was milder compared to previous post-pandemic seasons.
- Mycoplasma pneumoniae: The number of infections remained at an elevated level in 2024 and the beginning of 2025. Especially in summer and autumn 2024, it constituted a significant part of the disease burden with over 60% of total respiratory infections and more than 30% of hospitalizations.
- Vaccination coverage: Influenza and COVID-19 vaccination coverage was over 75% among the older portion of the population aged 65 years and above.
Figure 1 shows which viruses and bacteria contribute most to the overall burden of respiratory infections as well as the overall burden on the healthcare system measured by hospitalizations and hospitalizations with severe respiratory infection (SARI), by week.
Intensity levels in respiratory surveillance
In the 2024/25 season, disease-specific thresholds for respiratory viruses were introduced. This made it possible, week by week, to monitor the intensity of laboratory-confirmed cases and the number of hospitalizations for each of the three major respiratory viruses, figure 2.
In addition, a season start was defined for each virus. The season start is an important tool for the healthcare system. It indicates when virus circulation has reached a level where in the coming weeks one can expect:
- more visits to general practitioners and emergency departments
- more hospital admissions.
This helps the healthcare system to plan and prepare for increased pressure during the respiratory season.
Disease-specific data
Influenza
The influenza season 2024/25 was a very intense season starting in week 49, with number of cases and hospitalizations at high levels for several weeks, figure 2. The incidence only returned to low levels in week 18.
Circulating virus: Influenza A virus dominated the whole period with an equal distribution between influenza A(H1N1) and A(H3N2) until early 2025. After that, influenza A(H3N2) dominated.
Throughout the period, influenza B also co-circulated, figure 3.
Laboratory-confirmed cases: In 2024/25, 28,407 people were diagnosed with influenza, of which 22,840 were influenza A and 5,567 influenza B. By comparison, 19,203 were diagnosed in 2023/24 and 21,317 in 2022/23, figure 4. The highest incidence of influenza A in 2024/25 was seen among age groups 0-1 year and 85+, while for influenza B it was among age groups under 44 years.
Hospitalizations: In 2024/25, there were almost 7,111 influenza-related hospitalizations (25% of cases), in line with previous seasons. 6,585 were related to influenza A and 526 to influenza B. By comparison, there were 5,430 influenza-related hospitalizations in 2023/24 (28%) and 4,346 influenza-related hospitalizations in 2022/23 (20%). Influenza B mainly affects younger people, while most hospitalizations occur in older adults, so most hospitalizations were due to influenza A.
Deaths: In 2024/25, there were 582 influenza-related deaths (2.0% of cases), primarily in the oldest age groups and mainly related to influenza A. By comparison, there were 407 influenza-related deaths in 2023/24 (2.1%) and 268 influenza-related deaths in 2022/23 (1.3%).
Vaccination coverage: Vaccination uptake remained high in 2024/25 among the older portion of the population, with 85% of nursing home residents and 76% of people aged 65+ vaccinated. Among pregnant women, it was 23%.
Vaccine Effectiveness: In the 2024/25 season, persons aged 70 years and over were offered a new vaccine, which contains a so-called adjuvant, that strengthens the immune response, while the rest of the population was offered the traditional influenza vaccine. At the end of January, when the influenza incidence was at a high level, calculations of vaccine effectiveness (VE), across vaccine types and age groups, showed that more than half of influenza A cases – VE = 53% (47–58%) – and hospitalizations – VE = 52% (45–58%) – could be prevented.
When comparing VE for the new and the traditional vaccine type among persons aged 65 years and over, the calculations showed that the new adjuvanted vaccine could prevent nearly half of influenza A cases, 48% (42–52%), while the traditional vaccine prevented one third, 33% (24–41%).
It is well-known that vaccine effectiveness decreases throughout the season, and in week 20 in 2025, when the influenza incidence was at a low level, VE across age groups and vaccine types was 36% (33–39%). In comparison, VE in the age group 65 years and over was 40% (35–45%) for the new adjuvanted vaccine and 25% (17–33%) for the traditional vaccine.
Covid-19
It is still too early to conclude whether COVID-19 follows the same seasonal pattern as influenza and RSV. Compared with earlier periods, COVID-19 activity in 2024/25 (week 21 of 2024 to week 20 of 2025) was significantly milder.
In June 2024, an increase was seen in case numbers, SARS-CoV-2 concentration in wastewater, and hospitalizations. This led to the season start being declared in week 25.
Circulating virus: From the beginning until December 2024, JN.1 and subvariants such as KP.3.1.1 dominated. Then XEC recombinants took over, followed by new JN.1 subvariants from February onwards, figure 5.
Laboratory-confirmed cases and wastewater surveillance: In 2024/25, 12,345 persons tested positive for SARS-CoV-2. In comparison, 24,943 persons tested positive for SARS-CoV-2 in 2023/24, figure 6. In 2024/25, the highest SARS-CoV-2 incidence was found in the age group 65 years and over as well as in the age group 0–2 years.
The wastewater-based surveillance follows the same pattern as the surveillance of laboratory-confirmed cases and was at a lower level than in the previous three seasons, figure 7, as the SARS-CoV-2 concentration in the 2024/25 season has not been higher than medium level and for the majority of the season the incidence has been at a low level.
After the season start in week 25, both the wastewater concentration and laboratory-confirmed cases stabilized and remained at respectively a low and medium level until January 2025 without major weekly fluctuations in infection or hospitalizations, figures 6 and 7.
Hospitalizations: In 2024/25, there were 5,522 SARS-CoV-2-related hospitalizations (45% of the cases). In comparison, there were 10,179 SARS-CoV-2-related hospitalizations in 2023/24 (41% of the cases). In both 2023/24 and 2024/25, the highest SARS-CoV-2-related hospitalization incidence was in the oldest part of the population aged 80 years and over.
Vaccination coverage: Covid-19 vaccination coverage was also in 2024/25 at a very high level for the older part of the population, where 85% of nursing home residents and 75% of the elderly population aged 65 years and over were vaccinated. The coverage among pregnant women was 15%.
Vaccine effectiveness: Among persons aged 65 years and over who were offered seasonal vaccination against covid-19 in the 2024/25 season, a high and sustained protection against covid-19-related hospitalization and death was seen in the period from 1 October 2024 to 31 January 2025. The vaccine had an effectiveness of respectively 70% (62–77%) and 76% (63–85%) against covid-19-related hospitalization and death. No significant decline in protection was observed within four months after vaccination.
RSV (Respiratory Syncytial Virus)
The RSV 2024/25 season began in week 48, figure 1, which was later than the previous three post-pandemic seasons, and was less intense, figure 8.
Circulating virus: There was a co-circulation of RSV A (45%) and RSV B (55%). RSV B tended to dominate in the later part of the season, figure 9.
Laboratory-confirmed cases: In 2024/25, 8,308 persons tested positive for RSV. In comparison, 10,114 persons tested positive for RSV in 2023/24 and 11,917 in 2022/23. The highest RSV incidence in 2024/25 was, as in previous seasons, found in the age group 0–5 months, followed by the 6–11 months old children and the 1-year-olds.
Hospitalizations: In the 2024/25 season, 2,826 RSV-related hospitalizations were registered, which corresponds to 34% of all cases. In comparison, there were 3,252 RSV-related hospitalizations in the 2023/24 season (32% of the cases) and as many as 5,135 in the 2022/23 season, where 43% of RSV cases were hospitalized.
In all three seasons, the hospitalization incidence was highest among infants aged 0–5 months. Next followed children between 6 months and up to 2 years and persons aged 75–84 years as the most affected age groups.
Deaths: In 2024/25, there were 117 RSV-related deaths (1.4% of the cases), predominantly in the oldest age groups. In comparison, there were 109 RSV-related deaths in 2023/24 (1.1% of the cases) and 289 deaths in 2022/23 (2.4% of the cases).
Mycoplasma pneumoniae
In the spring and summer of 2024, the number of infections with M. pneumoniae remained elevated. In August of the same year, a further increase in the weekly cases was observed. This marked the beginning of a second wave of M. pneumoniae infections, where the number of weekly cases was higher than in the 2023/24 season, figure 10.
Laboratory-confirmed cases: In 2024/25, 40,742 persons tested positive for M. pneumoniae. In comparison, 14,636 persons tested positive for M. pneumoniae in 2023/24. The highest M. pneumoniae incidence in 2024/25 was, as in previous seasons, observed in the age group 6–12 years, followed by the 13–18-year-olds and the 0–5-year-olds.
Hospitalizations: In the 2024/25 season, 2,982 M. pneumoniae-related hospitalizations were registered, which corresponds to 7% of all cases. In the 2023/24 season, 1,608 patients (11%) were hospitalized in connection with an M. pneumoniae infection.
Sentinel surveillance monitors various respiratory viruses
Sentinel surveillance is based on reports from general practitioners and functions as a voluntary, sample-based reporting system that monitors influenza, COVID-19, and other respiratory virus infections. In the 2024/25 season, 107 general practices participated in the surveillance. The sentinel doctors report weekly how many patients with influenza-like symptoms (ILS) they see in their practice, as well as how many consultations they have in total.
The proportion of patients who contacted general practitioners with ILS remained low in the medium range throughout autumn and winter, with a gradual increase from week 49. The high consultation percentage in week 52 is considered falsely elevated due to fewer reports during the holiday period combined with fewer scheduled consultations. From the turn of the year, the consultation percentage increased further and remained stable in the medium range until week 10, figure 11. It should be noted that the consultation percentage is not specific to influenza virus but also includes other respiratory infections where patients present with influenza-like symptoms in general practice.
The sentinel doctors also submit swabs from a subset of patients with ILS. The season was characterized by a continued SARS-CoV-2 wave, which began in the summer of 2024. Entero-/rhinovirus dominated in the autumn months and until the turn of the year, after which influenza and RSV made up the majority of cases. As in previous seasons, an increase in parainfluenza virus was seen as the influenza incidence declined, as well as an increase in metapneumovirus in the spring of 2025.
In the 2024/25 season, SSI received 5,920 sentinel swabs in the period from week 40, 2024 up to and including week 20, 2025, which is fewer than in the previous season. Of these swabs, 3,443 (58%) were positive for at least one respiratory virus, and 145 adenovirus, 294 RSV, 682 entero-/rhinovirus, 390 endemic coronavirus, 237 SARS-CoV-2, 237 metapneumovirus, 158 parainfluenza virus, and 1,372 influenza virus were found. Compared to the latest season, more cases of entero-/rhinovirus, endemic coronavirus, and metapneumovirus were detected, while the other viruses occurred less frequently. The distribution of respiratory viruses among sentinel swabs is shown in figure 12.
This annual report is also covered in EPI-NEWS 22/2025.