On November 10, 2021, the Michigan Department of Health and Welfare (MDHHS) was notified by the University of Michigan Ann Arbor University Health Services (UHS) of a surge in influenza A (H3N2). Since this outbreak was part of the first substantive influenza activity during the COVID-19 pandemic, the CDC worked with universities, MDHHS, and regional partners to characterize and assist in controlling the outbreak. We conducted a survey to do so. Persons with COVID-19-like * or influenza-like illnesses evaluated by UHS since August 1, 2021 will be tested for SARS-CoV-2, influenza, and respiratory syncytial virus by rapid multimolecular assay. received.† Between October 6th and November 19th, a total of 745 laboratory cases of influenza were identified.§ Demographic information, viral genetic characteristics, and influenza vaccination history data were reviewed. This activity was carried out in accordance with applicable federal law and CDC policies.¶
Of the 3,121 people tested between October 6 and November 19, 745 (23.9%) were positive for influenza A and 137 (4.4%) were SARS-CoV-2, 84. Humans (2.7%) received respiratory syncytial virus test results. virus. Overall, more than 95% of influenza cases were detected between November 1st and 19th (figure), suggesting a rapid spread. One patient with confirmed influenza A infection was hospitalized. For patients with positive influenza tests, the median age is 19 years (range = 17-31 years), 54.1% are female, 60.0% live off campus, 34.6% live in on-campus dormitories, 5.4%. Is a house of fraternity or sorority. Of the 380 samples sequenced for influenza, all viruses belong to the A (H3N2) 2a.2 subgroup and recently the influenza A (H3N2) subclade 3C.2a1b.2a virus (ie, fullclade: 3C.2a1b.2a). ) Has diversified. 2). Of the 2,405 people tested for influenza A from October 6 to November 12, 128 out of 481 (26.6%) were positive for influenza and 512 of 1,924 were negative for influenza (26.6%). 26.6%) recorded visits from 2021 to 22. Influenza vaccine more than 14 days before the trial. ** **
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Number of symptomatic individuals tested for influenza A at university health services (N = 3,121) * and percentage of influenza A-positive tests by date of influenza test† — University of Michigan, October 6-19, 2021
* The first influenza A-positive test result was used among those who were tested multiple times between October 6th and November 19th, 2021. Or, if you never got a positive influenza A result, the first negative test result was used.
†The University Health Department does not carry out influenza A tests on Sundays.
The available influenza vaccines are designed to provide protection against four different influenza viruses: A (H1N1) pdm09, A (H3N2), B / Victoria strains, and B / Yamagata strains. Historically, influenza A (H3N2) virus has been less effective as a vaccine than influenza A (H1N1) pdm09 or influenza B virus. This is thought to be because the A (H3N2) virus evolves more rapidly and can escape immunity.[1] The A (H3N2) component of the Northern Hemisphere 2021–22 influenza vaccine was updated in February 2021 to protect against newly emerging 3C.2a1b.2a subclades containing two subgroups (2a.1 and 2a.2). increase.[2] The 2a.2 subgroup of H3N2 virus detected in Michigan is genetically associated with the 2a.1-like H3N2 virus contained in the Northern Hemisphere 2021-22 influenza vaccine, but is antigenically distinguishable (ie,). Low cross-reactivity of ferret antibody after infection).[3] Similar vaccination rates among people with positive and negative influenza tests at this outbreak suggest that protection against mild infection by the 2a.2 subgroup of the H3N2 virus was low among these most young adults. doing. However, this finding should be carefully interpreted due to possible incomplete vaccination history and changes in coverage due to ongoing vaccination campaigns. The individuals included in this analysis are mild flu illnesses, and vaccination rarely occurs in this age group and provides protection against a variety of outcomes such as hospitalization and death that are difficult to measure.[4] The results of this particular 2a.2 subgroup of H3N2 virus cannot be generalized to other age groups, high-risk populations, or other influenza viruses that may be endemic. Additional research and monitoring is needed to determine the effectiveness of the vaccine against other situations, people in other groups, and other influenza viruses that may emerge this season.
The results of this study highlight the importance of increasing vigilance against influenza disease this winter, as shown in the CDC’s Health Alert Network Health Advisory, published November 24, 2021. ..[5] Given the significant impact of COVID-19 on the healthcare system, there are more than 500 COVID-19 cases per 100,000 population in Michigan for the week ending November 19, 2021.[6] Additional strategies to reduce influenza illness are important. Some measures can help reduce the burden on severe influenza and the consequent medical services. First, improving influenza vaccination rates for people over 6 months of age, especially those at high risk of serious influenza complications, is important to reduce influenza-related illnesses, hospitalizations, and deaths. Compared to the flu vaccination rate in 2020, certain groups at high risk of severe influenza, such as pregnant people and children, have had lower vaccination rates so far this season. Second, clinicians should consider diagnostic tests for influenza and SARS-CoV-2 infections in patients with acute respiratory illness, especially among inpatients and patients at high risk of complications. Third, treatment with influenza antiviral drugs can reduce influenza complications, in all patients with suspected or diagnosed influenza in hospital, outpatients who develop progressive disease, and complications. Should be used for outpatients at high risk.[7] Influenza antivirals can also be used to reduce the risk of influenza in asymptomatic individuals exposed to influenza (that is, post-exposure prophylaxis).[7] Influenza antiviral drugs have historically been used for post-exposure prophylaxis of residents in facilities such as long-term care facilities to control the outbreak of influenza. In the context of the ongoing COVID-19 surge, influenza antiviral treatment and prevention have other communal environments (shelters, universities) to reduce the burden on medical services at these facilities during influenza. It can also be considered for those who live in dormitories, prisons, etc.). occurrence. Fourth, non-pharmaceutical interventions such as physical distance, masking, regular surface cleansing, hand hygiene, and proper cough etiquette used to prevent COVID-19 may also provide protection against influenza. there is.[8] To alleviate the potential severity of the flu season, public health professionals and clinicians should recommend and provide the current seasonal flu vaccine to all eligible individuals over 6 months. ..
