As we head into 2025, healthcare experts and the public alike are bracing for what is being referred to as the “2025 Winter Surge.” MedCram’s latest video takes a deep dive into what this surge might look like, based on past trends, current viral activity, and emerging health concerns. Whether you’re a healthcare professional or just someone trying to stay informed, understanding the potential challenges of this winter is crucial.
As the winter season sets in, we are once again witnessing a surge in respiratory illnesses across the United States. This year’s flu season has arrived later than expected, with influenza A, particularly the H1N1 strain from the 2009 pandemic, causing an alarming number of hospitalizations. Additionally, while COVID-19 cases remain on the lower side compared to previous years, there is concern over a potential resurgence. One of the biggest concerns this winter is the resurgence of Influenza A, particularly the H1N1 strain. This strain, originally part of the 2009 pandemic, has made a comeback and is affecting individuals across the country. In fact, many emergency room visits are reporting a significant rise in flu cases, particularly in the western United States. In Oregon, for instance, the percentage of emergency room visits attributed to the flu at the end of December 2024 was more than three times higher than the same period in 2023, highlighting the severity of the current flu season.
Flu Vaccine: Efficacy and Coverage
The flu vaccine is our primary defense against the seasonal virus, but this year, its effectiveness has been a topic of concern. The vaccine, which has been updated to contain a trivalent (three-strain) formula, targets H1N1 (pandemic 2009-like), H3N2, and a Victoria lineage B strain. While the effectiveness of the flu vaccine in the Southern Hemisphere showed a 35% reduction in hospitalization for high-risk groups, this is down from 50% in 2023. Early indications from the Northern Hemisphere suggest similar efficacy, which could explain the increased number of flu-related hospitalizations this season.
Another concerning trend is the decline in flu vaccine uptake since the COVID-19 pandemic. Data shows a significant drop in vaccine coverage compared to pre-pandemic years, with 2024-2025 seeing the lowest vaccination rates since 2019. The reduction in flu vaccine uptake may be contributing to the increased number of flu cases and hospitalizations this year.
A Swiss Cheese Approach to Prevention
The fight against influenza and other viral illnesses is not solely dependent on vaccination. The “Swiss cheese” model of prevention suggests that layers of protective measures can reduce the chances of infection. These layers include vaccination, antiviral treatments, good hygiene practices, and other preventive actions. While vaccines alone may not be 100% effective, each layer adds a level of protection that decreases the overall risk of infection, hospitalization, and death.
Antiviral medications can also help to mitigate the severity of symptoms, although they do not prevent infection. These medications may reduce symptoms by approximately 24 hours, which is a modest benefit but could be crucial for high-risk patients.
COVID-19: Less Severe, But Still Present
While COVID-19 is not expected to make a major comeback this winter, it is still a concern, particularly with the rise of newer variants. Modeling has suggested that the winter COVID-19 wave will not be as severe as in previous years, especially given the lack of a new immune-escape variant. The CDC’s data points to most COVID-19 infections being caused by the XEC variant, which is closely related to previous strains. Therefore, immunity from earlier infections or vaccinations may offer some level of protection.
In certain regions, like the Midwest, COVID-19-related emergency room visits are on the rise, although the numbers remain a fraction of what they were during previous winter peaks. Additionally, the CDC’s wastewater surveillance data has recently shown an increase in viral particles, indicating a potential uptick in cases. However, as the CDC reports, this increase in cases is not yet as dramatic as in past years, and it is hoped that immunity from prior exposure may keep severe cases at bay.
The Role of Bird Flu: A Growing Concern
Another viral illness that has garnered attention is bird flu (H5N1), which has recently made headlines in the United States. While it has not yet demonstrated person-to-person transmission, the H5N1 strain has caused a significant number of cases in animals, particularly birds, and has been fatal in some humans. Since the beginning of 2024, there have been 66 reported human cases, with the first fatality reported in Louisiana.
Fortunately, human-to-human transmission of H5N1 remains rare, and authorities continue to monitor the situation closely. However, the high mortality rate of H5N1, combined with its impact on wildlife, presents a serious threat to both public health and the agricultural industry. Efforts to contain the virus and prevent its spread are ongoing.
Environmental Factors: Sunlight, Temperature, and Humidity
What is driving these viral surges, and why do they seem to peak in the winter months? One factor to consider is the lack of sunlight during the winter. As the Earth tilts away from the Sun, the Northern Hemisphere experiences shorter days and lower levels of sunlight. This reduction in sunlight, along with colder temperatures, may contribute to the spread of influenza and other viral illnesses.
Interestingly, research has shown that sunlight exposure plays a significant role in reducing the incidence of influenza. A study published by the Harvard Kennedy School in 2020 demonstrated a strong correlation between sunlight levels and the spread of influenza. Areas with more sunlight exposure had lower flu incidence rates, while regions with less sunlight saw higher rates of infection.
Understanding the Timing of Viral Peaks
The timing of viral peaks is a consistent pattern observed year after year. The highest rates of influenza-related deaths typically occur a few weeks after the shortest day of the year, which falls around December 21st in the Northern Hemisphere. This pattern has been observed for decades and may be linked to the seasonal changes in sunlight and temperature. Interestingly, a similar peak in illness and death is seen in other conditions, such as heart disease and respiratory diseases, which also tend to spike in the winter months.
The 2025 winter viral surge is a complex interplay of factors, including the resurgence of influenza A, the ongoing presence of COVID-19, and emerging threats like bird flu. While the flu vaccine remains our best defense, its reduced efficacy and lower vaccination rates may be contributing to the current surge in cases. At the same time, environmental factors, particularly reduced sunlight, seem to play a key role in the seasonal spread of these viruses.
As we navigate this challenging season, it is essential to continue promoting vaccination, practicing good hygiene, getting sunlight exposure where possible and staying informed about the latest developments in viral outbreaks. By understanding the factors at play, we can better protect ourselves and our communities from the impact of winter viral surges.
LINKS / REFERENCES:
Flu emergency room visits now “very high” nationwide, CDC says (CBS) | https://www.cbsnews.com/news/influenz…
Interim Effectiveness Estimates of 2024 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Hospitalization — REVELAC-i Network, Five South American Countries, March–July 2024 (CDC) | https://www.cdc.gov/mmwr/volumes/73/w…
Influenza Vaccine Doses Distributed (CDC) | https://www.cdc.gov/fluvaxview/dashbo…
Wastewater COVID-19 National and Regional Trends (CDC) | https://www.cdc.gov/nwss/rv/COVID19-n…
CDC provides statement on first bird flu death (Channel 3000) | https://www.channel3000.com/news/cdc-…
Influenza-associated mortality in Australia, 2010 through 2019: High modelled estimates in 2017 (Vaccine) | https://www.sciencedirect.com/science…
Weather in Australia (Australia) | https://www.australia.com/en-us/facts…
Debunking the False Claim That COVID Death Counts Are Inflated (Scientific American) | https://www.scientificamerican.com/ar…
Autumn COVID‐19 surge dates in Europe correlated to latitudes, not to temperature‐humidity, pointing to vitamin D as contributing factor (Scientific Reports) | https://www.nature.com/articles/s4159…
Sunlight and Protection Against Influenza (Harvard Kennedy School) | https://www.hks.harvard.edu/publicati…
Cardiopulmonary and hematological effects of infrared LED photobiomodulation in the treatment of SARS-COV2 (Journal of Photochemistry and Photobiology B: Biology) | https://www.sciencedirect.com/science…