Many childhood illnesses aren’t fully captured by standard surveillance systems, potentially impacting our understanding of vaccine effectiveness and the true burden of disease. This underreporting isn’t necessarily a failure of data collection, but rather a complex issue stemming from how infections are identified and recorded.
The Challenge of Underreported Infections
Traditional methods of tracking infections, such as those relying on vaccination registries and surveillance data, can underestimate the actual number of cases. This is because not everyone who is infected seeks medical attention, and even when they do, infections aren’t always definitively diagnosed or reported. A study published in in the International Journal of Epidemiology highlights how this underreporting can introduce bias into vaccine effectiveness (VE) estimates.
Chiara Sacco, lead author of the study and part of the ECDC Fellowship Programme, and colleagues investigated how the magnitude and direction of this bias vary under different circumstances. The research emphasizes that under-ascertained and under-notified infections can skew our perception of how well vaccines are working.
Why Infections Go Unreported
Several factors contribute to the underreporting of infections. Mild cases often resolve without medical intervention. Parents may manage symptoms at home, particularly for common respiratory illnesses. Diagnostic testing isn’t always performed, even when a child sees a doctor. Informal clinical exchanges among pediatricians, as noted in research published on ScienceDirect, can sometimes provide early indications of emerging diseases, but these observations don’t always translate into formal reporting.
Recurrent respiratory infections are particularly common in children, and distinguishing between a new infection and a lingering effect of a previous one can be challenging. According to Verywell Health, multiple infections – such as more than three ear infections in six months – should prompt a medical evaluation, but even then, the underlying cause may not always be identified.
Impact on Vaccine Effectiveness Estimates
The study in the International Journal of Epidemiology demonstrates that underreporting can significantly affect VE estimates. If a substantial number of infections go undetected, the apparent effectiveness of a vaccine may be either overestimated or underestimated, depending on the specific circumstances. This is because the denominator – the total number of infections – is inaccurate.
The researchers found that the direction and magnitude of this bias depend on several factors, including the severity of the illness, the likelihood of seeking medical care, and the accuracy of diagnostic testing. Essentially, if mild infections are frequently missed, and the vaccine is more effective at preventing severe disease, the VE will appear higher than it actually is. Conversely, if mild infections are more common and the vaccine offers limited protection against them, the VE may be underestimated.
SARS-CoV-2 and Undocumented Infections
The issue of underreporting became particularly apparent during the COVID-19 pandemic. A study published in in Viruses, focusing on the pediatric population in the Tyrolean district of Schwaz, Austria, revealed a high prevalence of undocumented SARS-CoV-2 infections. Researchers, led by Teresa Harthaller, found that many infections went undetected, highlighting the limitations of relying solely on confirmed cases to assess the true extent of the pandemic and the immune response in children.
This research underscored the importance of considering the broader immunological picture, including humoral responses, to understand the durability of immunity following infection, even in the absence of a confirmed diagnosis.
Beyond Respiratory Infections
While the discussion often centers on respiratory viruses, underreporting affects other infections as well. Urinary tract infections (UTIs) in children, for example, require accurate diagnosis and tracking to monitor prevalence and treatment effectiveness. Comprehensive information on UTIs, including symptoms, diagnosis, and prevention, is available through resources like UpToDate, but even with these resources, not all cases are reported or accurately identified.
Implications for Public Health
Understanding the extent of underreporting is crucial for several reasons. Accurate VE estimates are essential for informing vaccination policies and public health recommendations. If VE is overestimated, it could lead to complacency and reduced vaccination rates. Conversely, if VE is underestimated, it could discourage vaccine uptake. A more accurate picture of the true burden of disease is needed to allocate healthcare resources effectively and to develop targeted interventions.
Addressing this challenge requires a multi-faceted approach, including improved surveillance systems, increased access to diagnostic testing, and greater awareness among healthcare providers and the public about the importance of reporting infections. Continued research, like the work by Sacco and colleagues, is vital to refine our understanding of the biases inherent in current data collection methods and to develop more accurate and reliable estimates of vaccine effectiveness and disease prevalence.
