Influenza Season 2023

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Last reviewed
September 25, 2023
Content Overview
Flu infections are seasonal as influenza viruses transition between northern and southern hemisphere in 2023.

Influenza Season September 2023

While seasonal influenza (flu) viruses are detected year-round, the exact timing and duration of any flu season varies by country, says the World Health Organization (WHO). Flu seasons in the Southern Hemisphere usually occur between April and September, while the Northern Hemisphere reports flu outbreaks between October through May most years. According to the WHO, the Pan American Health Organization (PAHO), the U.S. Centers for Disease Control and Prevention (CDC), and the U.K. Health Security Agency, what happens in one hemisphere does not necessarily predict what will happen in the other because influenza viruses change and impact populations differently. On September 4, 2023, the WHO published Influenza Update N° 454, indicating that influenza detections remained low globally, with activity in many southern and Oceania countries decreasing.

An analysis published by the Journal of Infectious Diseases on August 1, 2023, found the risk of flu-related intensive care unit admission was seven times greater in lower-middle-income countries (LMIC). The risk of mechanical ventilation and in-hospital death also increased fourfold in LMIC.

Flu Season in the Americas

The Pan American Health Organization (PAHO) says flu viruses are transmitted easily from person to person via droplets and small particles produced when infected people cough or sneeze. The PAHO published a Regional Update for Epidemiological Week #34, which reported influenza activity has remained at low levels in North America. Influenza activity has decreased in the Caribbean and Central America in the last few weeks. The U.S. CDC reported in August 2023 that there is limited data available on flu-related hospitalizations in Southern Hemisphere countries.

Flu Season Australia

In Oceania, influenza activity decreased with influenza A(H1N1)pdm09 and influenza B viruses predominant. Australia's Department of Health and Aged Care published report No. 11, which stated the impact on society due to the 2023 influenza season was decreasing. Since seasonal surveillance commenced in 2023, there have been 209 (7%) ICU admissions and 239 related deaths as of September 3, 2023. Current influenza immunization data was posted through September 2023, says it is too early to assess vaccine effectiveness for this flu season. The 2022 Australian Influenza Surveillance Report provides a national influenza season summary.

Flu Season Europe

On September 4, 2023, the WHO reported indicators of influenza activity at low levels or below the seasonal threshold in most reporting countries in the temperate zones of the northern hemisphere. Detections were predominantly influenza A(H1N1) pdm09, followed by influenza B and influenza A(H3N2) viruses. The European CDC reported on July 7, 2023, following a peak at the end of 2022 at 42%, followed by a decrease until week 4/2023 when it reached 22% positivity before rising again to fluctuate around 28% positivity between week 5−12/2023. Since then,  influenza activity has been decreasing across the European Region.

Flu Season Mexico

In the Central American countries, influenza activity decreased overall as of late August 2023. During the last four epidemiological weeks, the predominant influenza viruses have been influenza A, mainly A(H1N1)pdm09, with concurrent circulation of influenza A(H3N2) and influenza B/Victoria to a lesser extent.

Flu Season United States

In the United States, flu activity usually peaks between December and February, although significant activity can last as late as May, says the U.S. Centers for Disease Control and Prevention (CDC). The U.S. CDC FluView week #37 report confirmed on September 22, 2023, that seasonal flu rates last week were low nationally, with 315 (0.8%) positive specimens reported. Last week, 820 patients with laboratory-confirmed influenza were admitted to a hospital, an increased number since the previous report. The U.S. National Center for Health Statistics mortality surveillance data on September 21, 2023, confirmed that 13 additional influenza-related deaths were reported. The CDC confirmed that 176 influenza-associated pediatric fatalities have been reported during the 2022-2023 flu season. The CDC's Clinician Outreach and Communication Activity webinar on August 31, 2023, presented an Update for Pediatric Providers regarding the 2023-2024 Recommendations for Influenza Prevention and Treatment in Children. The CDC publishes an Influenza Summary Update map.

The Walgreens Flu Index highlights local flu activity compiled using retail prescription data for antiviral influenza medications - last updated on September 16, 2023.

Flu Season United Kingdom

In the U.K., as of September 14, 2023, the Respiratory Datamart reported in week #37, influenza positivity remained low and stable at 0.8% up to week #36. Through primary care surveillance, the influenza-like-illness consultations indicator remained stable in week 36 compared to the previous week and was within the baseline activity level range. No influenza-confirmed outbreaks were reported in England, and there were three influenza ICU admissions in week 36.

Influenza Vaccines

Flu shots news for the 2023-2024 influenza season is published by Precision Vaccinations.

RSV Season

Respiratory syncytial virus (RSV) season 2023 trends are published by Precision Vaccinations.

Influenza, RSV, SARS-CoV-2 Coinfections

Overall, tests revealed that coinfections with two or more viruses occurred in 1.33% of positive results and .55% of the studied samples. The positivity rates varied by the viruses involved, ranging from .38% in adults for SARS-CoV-2 and RSV to 2.28% in adults for influenza A and SARS-CoV-2. However, coinfection rates in the pediatric group were higher than in the adult population for all three viruses. Pratt noted that his team was surprised by the high 6% coinfection rate of SARS-CoV-2 and influenza A in those under 21.

Influenza Mortality 2023

The JAMA Network published in February 2022 results from a peer-reviewed influenza mortality study that found from 1999 to 2018, there were 10,171 (95% CI, 9652-10 691) underlying respiratory deaths per year, with 23 deaths (95% CI, 19-27) among children younger than one year in the U.S.