Current High Severe Flu Season - Worst Since at least 2017/18
Although I got my flu vaccine in October - given the amount of flu out there right now, my age, and the limits of protection offered by the flu jab - I feel it is only prudent to wear a mask in public. So far, this `layered' protection scheme has kept me without a sniffle for the past 4 years.
While I firmly believe that the seasonal flu vaccine reduces morbidity and mortality, and have gotten the jab every year now for more than two decades, I've written often about the dangers of `overselling' its benefits to the general public (see here, here, and here).Up until about a dozen years ago, the oft repeated mantra from the CDC was: ". . . for healthy adults under the age of 65, in years when the vaccine is a good match to circulating strains, effectiveness ranges from 70%-90%."In 2011 the CDC lowered expectations somewhat, stating in a FAQ: `. . . recent RCTs of inactivated influenza vaccine among adults under 65 years of age have estimated 50-70% vaccine efficacy during seasons in which the vaccines' influenza A components were well matched to circulating influenza A viruses.'
But over the past decade we've seen flu shots struggle to even reach that 50% vaccine effectiveness (VE) mark, particularly when H3N2 influenza was the dominant subtype. A few (of many) blogs on these less-than-stellar results include:
MMWR: Reduced Protection From This Year’s Flu Vaccine (2015)Since many people who got the annual flu shot still got the flu, faith in its ability to protect against the virus has suffered. Add in COVID fatigue and a growing distrust of vaccines - uptake of the seasonal flu shot for those under the age of 18 peaked in 2019 (see chart below) - and has dropped by roughly 10% since.
PLoS Path.: A Structural Explanation For The Low VE Of Recent H3N2 Vaccines (2017)
Eurosurveillance: Early Season Flu Surveillance & Vaccine Effectiveness (VE) - Canada (2018)
Analysis shows last year’s flu vaccine 36% protective against H3N2 strain (2022)
This new message - that even if the flu vaccine doesn't always prevent infection, it can often reduce the severity of one's illness - is a step in the right direction.
Today we've a study - published in the European Respiratory Review - of influenza vaccine effectiveness in preventing both infection - and serious illness - in children, adults, and the elderly which confirms the flu only provides limited protection against infection, but significant protection against serious illness or death.
This meta-analysis draws from studies from 38 countries, involving 6.5 million patients, finds that the flu shot reduces infections in children, adults, and the elderly against H1N1 and influenza B, but is less effective in preventing infection with H3N2 in the elderly.
Despite higher levels of H3N2 infection in the elderly, they still benefited by its reduced severity due to the vaccine.
This is a lengthy, detailed, meta-analysis and there is a lot here to unpack. You'll want to follow the link to read it in its entirety, but the take-away is pretty simple:
Even if the flu vaccine doesn't always fully protect you against a breakthrough infection, it is still highly effective in preventing more serious illness or death.And during a viral storm such as we are seeing right now, any advantage you can get is worth having.
Influenza vaccine outcomes: a meta-analysis revealing morbidity benefits amid low infection prevention
Jesus Presa Javier Arranz-Herrero Laura Alvarez-Losa
European Respiratory Review 2025 34(175): 240144;
Abstract
Background
The morbidity and mortality associated with influenza viruses are a significant public health challenge. Annual vaccination against circulating influenza strains reduces hospitalisations and increases survival rates but requires a yearly redesign of vaccines against prevalent subtypes. The complex genetics of influenza viruses with high antigenic drift create an ongoing challenge in vaccine development to address dynamic influenza epidemiology. Understanding the evolution of influenza viruses and the vaccine's effectiveness against different types and subtypes is pivotal to designing public health measures against influenza.
Methods
We conducted a systematic review and meta-analysis of 192 705 patients, collecting information on the incidence and severity of the disease. The results of this meta-analysis were further validated using data from 6 594 765 patients from TriNetX. We analysed the prevalence of the most common influenza A virus (IAV) subtypes (H1N1 and H3N2) and influenza B virus (IBV), as well as vaccination effectiveness against them in three age groups, given that age is associated with influenza disease severity.
Results
Our analysis reflects that overall vaccination against H1N1 IAV and IBV is effective in reducing infection and influenza-related complications in children aged <5 years old, individuals between 5 and 65 years old and older adults aged >65 years old. By contrast, while vaccination against H3N2 IAV is effective in protecting against infection in infants <5 years old, it provides reduced protection against infection in older individuals.
Conclusions
Despite higher infection rates, vaccination against H3N2 remains as highly effective as vaccination against H1N1 and IBV in reducing influenza-related morbidity and mortality in all age groups. Detailing vaccine effectiveness in terms of infection protection and disease burden across different age groups is necessary for understanding vaccine impacts in terms of other outcomes, e.g. hospitalisations, mortality and disease severity; for improving vaccine formulations and public awareness; and for enhancing vaccination campaigns to improve coverage and public acceptance.
Shareable abstract @ERSpublications
We need to shift the vaccination message to emphasise infection prevention and protection against severe outcomes. The emphasis on flu vaccination should be on preventing severe illness versus infection. https://bit.ly/3ZR6Nl7
(SNIP)
Influenza vaccination offers significant protection against mortality for up to 12 months post-infection (figure 4). This was particularly evident in individuals >65 years old, especially against H1N1 and H3N2 IAV infections, with less pronounced effects observed for IBV. However, the analysis based on the TriNetX dataset demonstrated a decline in vaccine effectiveness in terms of preventing death over time, which was notably more pronounced for H3N2; thus, annual vaccination, with optimal effectiveness observed when administered shortly before the influenza season, is an important current practice for reducing in-hospital influenza-related death.
Additionally, vaccination correlates with a reduction in the incidence of co-infection with secondary pathogens associated with pneumonia, a leading cause of mortality among influenza-infected patients [11]. In the case of IBV, the data presented may not indicate any apparent influenza vaccination protection from death. However, this result has to be interpreted with caution and taking other facts into consideration. IBV infections were associated with a lower mortality risk compared with IAV infections (figure 4b, c) in all the pre-existing conditions analysed using the TriNetX dataset (figure 5a). However, further studies are required to better understand this issue, such as understanding the patient's immune status and the comorbidities of hospitalised IBV-infected patients. In fact, some studies performed in certain countries showed similar or higher mortality rates for IBV compared to IAV [24–27]. Therefore, maintaining vaccination efforts is both necessary and beneficial.
