Quantified impacts of non-pharmaceutical interventions on influenza circulation during the COVID-19 pandemic in 13 African countries, 2020-2022

Shifts in Respiratory Virus Epidemiology on Reunion Island From 2017 to 2023: Impact of COVID-19 Pandemic and Non-Pharmaceutical Interventions

Background

The COVID‐19 pandemic has reshaped the landscape of respiratory viral infections globally. This study examines these changes on Reunion Island, a French department in the southeastern Indian Ocean.

Methods

Retrospective data from 2017 to 2023, from over 24,000 samples collected across the hospital system, partner laboratories, and a network of sentinel physicians, were analyzed and correlated with the number of consultations at the hospital emergency department and with sentinel physicians for symptoms of acute respiratory infections (ARIs). The epidemiology of respiratory viruses was analyzed by comparing the pre‐ and post‐COVID‐19 periods to assess disruptions in seasonal patterns, changes in virus prevalence, and the affected age groups.

Results

Our database effectively captured the epidemiology of respiratory infections across the island, as demonstrated by its strong correlation with the number of consultations for ARI. Post‐COVID‐19, the influenza virus exhibited multiple epidemic waves within a single year, deviating from its traditional single annual peak and showing a significant decline in circulation from 2020 to 2023. The circulation of respiratory syncytial virus was also impacted post‐COVID‐19, with epidemics starting earlier and lasting longer compared with pre‐COVID‐19 years. Human rhinovirus circulated more prominently in the post‐COVID period, accounting for up to one‐third of positive cases, becoming the most prevalent respiratory virus (excluding SARS‐CoV‐2).

Conclusions

These findings suggest a notable impact of the COVID‐19 pandemic and associated NPIs on respiratory virus circulation on Reunion Island since mid‐2020. They underscore the complex interplay between viral interference, public health interventions, behavioral changes, and youth immunity, emphasizing the need for adaptable strategies in managing respiratory virus outbreaks in the post‐COVID‐19 era.

Insights into Genetic and Antigenic Characteristics of Influenza A(H1N1)pdm09 Viruses Circulating in Sicily During the Surveillance Season 2023-2024: The Potential Effect on the Seasonal Vaccine Effectiveness

After disruption in the influenza circulation due to the emergence of SARS-CoV-2, the intensity of seasonal outbreaks has returned to the pre-pandemic levels. This study aimed to evaluate the evolution and variability of whole-genome sequences of A(H1N1)pdm09, the predominant influenza virus in Sicily (Italy) during the season 2023-2024. The potential vaccine efficacy was calculated using the pepitope model based on amino acid changes in the dominant epitope of hemagglutinin. The HA gene sequences showed several amino acid substitutions, some of which were within the major antigenic sites. The phylogenetic analysis showed that Sicilian strains grouped into two main genetic clades (6B.1A.5a.2a.1 and 6B.1A.5a.2a) and several subclades. Notably, about 40% of sequences partially drifted from the WHO-recommended vaccine strain A/Victoria/4897/2022 for the Northern Hemisphere. These sequences mostly belonged to the subclades C.1.8 and C.1.9 and harboured the amino acid mutations responsible for the modest predicted vaccine efficacy (E = 38.12% of 53%, pepitope = 0) against these viruses. Amino acid substitutions in other gene segments were also found. Since influenza viruses are constantly evolving, genomic surveillance is crucial in monitoring their molecular evolution and the occurrence of genetic and antigenic changes, and, thus, their potential impact on vaccine efficacy.

Impact of the COVID-19 Pandemic on Influenza Hospital Admissions and Deaths in Wales: Descriptive National Time Series Analysis

Background

The COVID-19 pandemic and the ensuing implementation of control measures caused widespread societal disruption. These disruptions may also have affected community transmission and seasonal circulation patterns of endemic respiratory viruses.

Objective

We aimed to investigate the impact of COVID-19-related disruption on influenza-related emergency hospital admissions and deaths in Wales in the first 2 years of the pandemic.

Methods

A descriptive analysis of influenza activity was conducted using anonymized pathology, hospitalization, and mortality data from the Secure Anonymised Information Linkage Databank in Wales. The annual incidence of emergency hospitalizations and deaths with influenza-specific diagnosis codes between January 1, 2015, and December 31, 2021, was estimated. Case definitions of emergency hospitalization and death required laboratory confirmation with a polymerase chain reaction test. Trends of admissions and deaths were analyzed monthly and yearly. We conducted 2 sensitivity analyses by extending case definitions to include acute respiratory illnesses with a positive influenza test and by limiting admissions to those with influenza as the primary diagnosis. We also examined yearly influenza testing trends to understand changes in testing behavior during the pandemic.

Results

We studied a population of 3,235,883 Welsh residents in 2020 with a median age of 42.5 (IQR 22.9-61.0) years. Influenza testing in Wales increased notably in the last 2 months of 2020, and particularly in 2021 to 39,720 per 100,000 people, compared to the prepandemic levels (1343 in 2019). The percentage of influenza admissions matched to an influenza polymerase chain reaction test increased from 74.8% (1890/2526) in 2019 to 85.2% (98/115) in 2021. However, admissions with a positive test per 100,000 population decreased from 17.0 in 2019 to 2.7 and 0.6 in 2020 and 2021, respectively. Similarly, deaths due to influenza with a positive influenza test per 100,000 population decreased from 0.4 in 2019 to 0.0 in 2020 and 2021. Sensitivity analyses showed similar patterns of decreasing influenza admissions and deaths in the first 2 years of the COVID-19 pandemic.

Conclusions

Nonpharmaceutical interventions to control COVID-19 were associated with a substantial reduction in the transmission of the influenza virus, with associated substantial reductions in hospital cases and deaths observed. Beyond the pandemic context, consideration should be given to the role of nonpharmaceutical community-driven interventions to reduce the burden of influenza.