Weekly / October 28, 2022 / 71(43);1353–1358
María Fernanda Olivares Barraza, MG1,* ; Rodrigo A Fasce2,*; Francisco Nogareda, MPH3; Perrine Marcenac, PhD4; Natalia Vergara Mallegas1; Patricia Bustos Alister, MSc2; Sergio Loayza, MD3; Anna N. Chard, PhD4; Carmen Sofia Arriola, PhD4; Paula Couto, MD3; Dr. Christian García Calavaro, DrPH1; Angel Rodriguez, MD3; David E. Wentworth, PhD4; Cristobal Cuadrado, MD, DrPH1; Eduardo Azziz-Baumgartner, MD4 (View affiliations)
What do we already know about this topic?
Influenza transmission has replaced the COVID-19 pandemic.
What does this bring?
In 2022, influenza A(H3N2), clade 3C. 2a1b. 2a. 2, circulated in Chile months before the pre-pandemic influenza seasons and was linked to 1,002 hospitalizations. Flu vaccination reduced the threat of A(H3N2) hospitalization by 49%
What are the implications for public practice?
Like some countries in the Southern Hemisphere in the 2022 flu season, countries in the Northern Hemisphere would likely face atypical timing and intensity flu activity in the 2022-23 season. The health government deserves to inspire all other eligible people to get a flu vaccine and take precautions to reduce flu transmission (e. g. , avoid close contact with others with health problems).
The COVID-19 pandemic has affected influenza virus transmission, with traditionally low activity, atypical timing, or altered duration of influenza seasons during the 2020-22 era (1,2). Community mitigation measures implemented since 2020, adding physical distancing and the use of face masks, have been attributed, in part, to lower global influenza detections during the pandemic, compared to pre-pandemic seasons (1). Lower population exposure to herbal influenza infections in 2020-2021 and easier network mitigation measures post-pandemic. the advent of COVID-19 vaccines may simply raise the possibility of serious influenza outbreaks. Partners in Chile and the United States evaluated influenza activity in the southern hemisphere and estimated influenza hospitalization rates and vaccine effectiveness (VE) across age organization in Chile in 2022. Peak Season of recent influenza in Chile began in January 2022, pre-pandemic seasons, and was primarily related to influenza A(H3N2), class 3C. 2a1b. 2a. 2. Cumulative occurrence of hospitalizations for pneumonia and influenza (P
The occurrence of influenza was estimated using the knowledge of hospital discharge from the Ministry of Health (MINSAL), the Health Statistics and Information Decomponent, and the knowledge of viral surveillance from the National Influenza Center (NIC). Chile records all hospital-consistent and public hospital patient discharge diagnoses in a central knowledge set. A subset of breath samples from these patients were analyzed using the CDC’s opposed transcription-polymerase chain reaction (RT-PCR)† protocols for clinical care of the influenza virus regimen or as a component of surveillance. national respiratory virus. The epidemic threshold used to delimit the influenza season was explained as the average of the consistent weekly percentage of positive patterns verified through the NIC of the period 2017-2019. The start of the influenza season for each calendar year from 2017 to 2019 and through 2022 was explained as the epidemiologic week in which the consistent percentage of influenza-positive specimens exceeded the old epidemic threshold for ≥ 3 weeks. Strategies described in the past (3) were used to estimate the cumulative occurrence of influenza hospitalizations. Only certain International Classification of Diseases, Tenth Revision (ICD-10) (J09-18) P&I discharge diagnosis codes were considered attributable to influenza viruses, as providers typically make those diagnoses in the absence of controls from laboratory. To characterize influenza P&I diagnoses, the consistent percentage of severe acute respiratory infection (SARI) patients recruited from nine sentinel sites§ with verified influenza-positive specimens at the NIC was implemented for unverified patients with a P&I diagnosis. Patients with SARI with a positive pattern for influenza were calculated for each one month and for each one an age organization (<5, 5–18, 19–64 and ≥65 years). A similar proportion of other people diagnosed with P&I were assumed to test positive for influenza (Supplementary Table; https://stacks. cdc. gov/view/cdc/121863). To minimize misclassification, only cases in which P&I was the number one hospitalization-related diagnosis were included in calculations estimating the proportion of P&I cases attributable to influenza. The organization-specific proportion by age was calculated through the organization by age and month, summed for each of the organizations by age, divided by the number of other people in that organization by age for that year, then multiplied by 100,000 to download the occurrence consistent with 100,000 consistent conson-years.
In 2022, Chile used Abbott INFLUVAC, a southern hemisphere trivalent egg-based influenza vaccine formulation containing antigens from a virus type A/Victoria/2570/2019 (H1N1)pdm09, A/Darwin/9/2021 ( H3N2) and B/Austria /1359417/2021-like virus (lineage B/Victoria) (4). The SARI sentinel knowledge submitted to the Network for the Evaluation of the Efficacy of the Vaccine in Latin America and the Caribbean against Influenza (REVELAC-i) of the Pan American Health Organization was used to estimate the effectiveness of this vaccine in prevention of influenza hospitalizations using the strategies described in the past (5). REVELAC-i used a negative verification case design to calculate the probability that a hospitalized patient with a severe respiratory infection and a positive influenza verification result (case-patient) had ever been vaccinated against influenza compared to the probability that a hospitalized patient with similar illness but negative for influenza (patient) had been vaccinated. Patients with positive effects on SARS-CoV-2 RT-PCR control (6) were excluded from the organization. VE estimates were calculated as 1-odds ratio x hundred and adjusted for age, month of symptom onset, and pre-existing conditions. This report was reviewed through MINSAL and conducted in accordance with applicable laws. ¶ This activity was reviewed through CDC and conducted in accordance with applicable federal law and CDC policy. **
In 2022, Chile’s NIC tested 59,392 respiratory samples through its national network of laboratories, of which 3,140 (5. 3%) tested positive for SARS-CoV-2 and 4,070 (6. 9%) for influenza. Of the positive samples for influenza, 2204 (54%) were typed and all but one (2203; >99. 9%) were influenza A(H3N2) viruses; the remaining specimen was an influenza A(H1N1) virus. In 2017, 2018, and 2019, the influenza epidemic threshold was 6. 2%, and the onset of the flu season occurred at weeks 18, 21, and 17, respectively, corresponding to an early influenza season from April through May. In contrast, in 2022, the percentage of positive samples for influenza first exceeded and remained above this epidemic threshold of weeks 1 through 6 (January-February), was below the epidemic threshold of weeks 7 through 17, and then exceeded it again from week 18 (May 2020). ); the peak of activity occurred week 24 (June) (Figure). The 280 (12. 7%) influenza virus samples sequenced by next-generation sequencing were from influenza A(H3N2), clade 3C. 2a1b. 2a. 2.
From January to August 2022, a total of 17,752 (0. 1%) more people from the Chilean population (19,828,563) were hospitalized for the treatment of P
Overall, 1,002 (5. 6%) of 17,752 P hospitalizations
Among the people who preceded influenza vaccination in Chile in 2022 (adults older than 65 years, older than 11 to 64 years with chronic diseases, pregnant women, infants and young people older than 6 months to 10 years and some other people§§) who counted for 41% ≥of the general population, 92. 5% were vaccinated. Although the 2022 Southern Hemisphere vaccine formulas were not available prior to the first wave of nonseasonal influenza at weeks 1 through 6, approximately 88% of vaccinated Americans got their vaccine before flu activity peaks in 2022 at week 24.
The sentinel surveillance knowledge sent to REVELAC-i used to estimate EVs for Chile included 717 negative patients and 175 patient-cases. Of 175 patient-cases, 118 (67%) tested positive for A(H3N2) and one for A(H1N1)pdm09. Crude and adjusted EV estimates for hospitalization associated with influenza A(H3N2) were 46% (95% CI = 17% to 65%) and 49% (95% CI = 23% to 67%), respectively.
The 2022 Chilean flu outbreak began months before a typical flu season (7) and resulted in 1002 flu-related hospitalizations and infections. seasons prior to the COVID-19 pandemic, is much higher than in 2020-2021, when the detection of influenza virus in Chile is low. trends observed in other countries of the southern hemisphere in 2022, adding Australia, Argentina and Peru; the onset of influenza seasons in South Africa corresponded to pre-pandemic seasons and was characterized by an initial predominance of A(H1N1)pdm09 viruses, followed by B/Victoria viruses. ¶¶
To reduce influenza-associated morbidity, the Chilean government vaccinated more than 90% of other people prioritized for vaccination free of charge. Although these vaccines are only available after the first wave of influenza (weeks 1 to 6), the Chilean government effectively vaccinated 88% of the target population before the peak of influenza activity in week 24. Influenza Vaccines were 49% effective in preventing hospitalizations this season predominantly A (H3N2) clade 3C. 2a1b. 2a. 2. The 2022-2023 Northern Hemisphere influenza vaccine formulations comprise the same A(H3N2) clade and antigen (3C. 2a1b. 2a. 2 and A/Darwin/9/2021, respectively) that are used in the Northern Hemisphere influenza vaccine. southern hemisphere 2022; if clade A(H3N2) 3C. 2a1b. 2a. 2 also predominates in the 2022-2023 Northern Hemisphere influenza season, these Northern Hemisphere formulations would likely be equally effective in preventing severe influenza illness. Like some jurisdictions in the southern hemisphere, Chile has known a limited number of cases of influenza B virus, none of which were subtype B/Yamagata. The general absence of B/Yamagata may also imply that this subtype has become rare (8); however, continuous monitoring is needed to know if it will reappear in long seasons.
The conclusions of this report are subject to at least 3 limitations. First, the dominant circulating subtype was taken according to the typing of 54% (2204 of 4070) of breathing samples that tested positive for influenza virus, and the dominant clade was formed. thinking about sequencing 13% of samples (280 out of 2203); Therefore, it is conceivable that no other types of viruses and clades have been identified. Second, EV estimates are based on a limited number of hospitalized case patients and control patients from nine hospitals, and unmeasured confounding, adding confusion related to hospitalization or vaccination. , would possibly be provided in this body of knowledge. Finally, knowledge about testing and hospitalization would likely have been affected by adjustments in care-seeking behavior due to the COVID-19 pandemic that was not assessed in those analyses.
This knowledge of the 2022 influenza season in Chile implies that influenza activity in the Southern Hemisphere was atypical, most likely due to the continued effects of the emergence of SARS-CoV-2 in 2020. Strict adherence to network mitigation measures (9) and top influenza vaccination policy likely mitigated the emergence of influenza in Chile in the 2022 season. Northern hemisphere countries can gain advantages in preparing for an atypical season, which may come with early influenza activity with potentially severe illness for the 2022-23 season. especially in the absence of preventive measures, adding vaccination. Health officials deserve to inspire communities to protect themselves by getting a flu shot in accordance with CDC recommendations and taking precautions to decrease flu transmission, adding to avoid close contact with others with health problems (10).
John Barnes, Rebecca Kondor, Juliette Morgan, Sonja Olsen, CDC; Rafael Bralic Araos, Universidad del Desarrollo.
Corresponding authors: Rodrigo A. Fasce, rfasce@ispch. cl; María Fernanda Olivares Barraza, maria. olivares@minsal. cl.
1Ministry of Health, Santiago, Chile; 2Department of Virology, Institute of Public Health of Chile, Santiago, Chile; 3Pan American Health Organization, Washington, DC; 4Division of Influenza, National Center for Immunization and Respiratory Diseases, CDC.
* Data rows are 3-week moving averages aligned to the right of the percentage of samples tested for influenza virus.
† Data 2022 to epidemiological week 36.
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