Influenza trending upward with higher-than-expected mortality among people over 45

According to the Ricardo Jorge Institute, in the 2023/2024 season there were 38,771 cases of respiratory infections and 6,262 cases of influenza in hospitals, indicating higher than expected mortality from all causes in people over 45 years of age.

According to the latest Epidemiological Surveillance Bulletin of Influenza and Other Respiratory Viruses prepared by the National Institute of Health Dutor Ricardo Jorge (INSA) and covering the period from December 25 to 31 (week 52), 36 cases of influenza were reported. 21 intensive care units (ICUs) that sent information.

Of these 36 cases, influenza A(H1N1) virus was identified in one case, influenza A virus was not subtyped in 34 cases, and the virus type could not be determined in one case. Of the sick people, 32 had a chronic disease, 33 had a recommendation for vaccination against seasonal influenza, but only nine were vaccinated (information is unknown in six cases).

Since the start of the surveillance season (October 2), intensive care units collaborating on surveillance have reported 85 cases of influenza. Of the total cases, 85.9% (73) had an underlying chronic disease and 91.8% (78) had a recommendation for seasonal influenza vaccination, but only 36.1% (22) were vaccinated.

Over the last week of the year, 1472 positive cases of influenza virus were identified, of which 1372 were type A and 49 were type B. In 147 cases, subtype A(H1) was detected, in 14 – subtype A(H3).

The bulletin also states that of the samples analyzed since the start of surveillance in the 2023/2024 season (October 2), influenza A(H1) virus was detected in 88.7% of influenza cases.

Since October, 118 cases of co-infection with the influenza virus and SARS-CoV-2, which causes Covid-19, have also been identified.

According to INSA, since the beginning of the surveillance season, other respiratory viruses have been identified in 106 cases of acute respiratory infection/influenza syndrome (ARI/FH), including three cases of co-infection. The following viruses were identified: rhinovirus (67), respiratory syncytial virus (17), coronavirus (6), parainfluenza (13), adenovirus (1) and enterovirus (5).

For respiratory syncytial virus (RSV), INSA reports epidemic activity “with a likely downward trend” in the number of new hospitalizations in children under two years of age. However, the institute said the trend “should be interpreted with caution” given potential notification delays and the impact of the holiday period.

INSA also states that the majority of subtype A(H1) viruses characterized to date (73%) have similar genetic characteristics to the virus included in the 2023/2024 influenza vaccine, but emphasizes that subtype A (H3N2) viruses are characterized by Thus. far from having “a set of genetic mutations relative to this season’s vaccine virus,” which is considered “genetically distinct” from the strain included in the flu vaccine.

According to the bulletin, the proportion of flu patients in intensive care units has been increasing over the past two weeks, reaching 17.1% in the last week of the year, higher than rates recorded in similar periods.

The Ricardo Jorge Institute also recalls that the European Center for Disease Prevention and Control (ECDC) states that “non-pharmacological measures had an impact on the low circulation of respiratory pathogens and a decrease in population immunity, which could exacerbate the impact of respiratory infections.” diseases this winter.”

“Thus, the increase in the proportion of influenza cases in intensive care units observed at week 52/2023 may reflect increased influenza virus circulation in settings of increased social interaction, without personal protective measures, following a period of decreased circulation. during the Covid-19 pandemic,” he adds.