Seasonal variation in the incidence of diseases has been observed for centuries, dating back at least to ancient Greece, and
yet scientific understanding of its underlying mechanisms remains relatively rudimentary for many diseases.1 Seasonality is not only an important factor in common infectious diseases—such as influenza, chickenpox, and measles—but
also in noninfectious diseases such as seasonal affective disorder (SAD) and rheumatoid arthritis (RA).
Place that next to clinical development, which at the best of times is a complex, long, frustrating process in an ever-changing
regulatory environment, and you have an unenviable task for clinical trial managers. Clinical trial managers must make considerable
logistical decisions and need significant depth of knowledge, including but certainly not limited to: planning timelines and
projecting and managing budgets whilst at the same time ensuring the delivery of a high-quality product. However, management
for seasonal diseases adds to this complexity in regard to fluctuations in the incidence of the disease studied; the recruitment
of patients to coincide with a particular part of the year (dependent on latitude, of course); and the attentiveness to unexpected
changes in the pattern of the disease and their implication on the running of the clinical trial.
Mathematical modelling has provided the advancement necessary to take the hypotheses of seasonality and apply them to the
field. Nevertheless, given the complexity of seasonality, a serious limiting factor to quantitative analyses and predictive
models of disease patterns is the lack of long-term disease records with similar data collected over a network of spatial
There are a multitude of complexities associated with running a clinical trial where a seasonal disease is the target, or
could impact the trial itself. But there are strategies that can allow for the control and quality seen in less complex trial
management to be transferred to the ever variable field of seasonal diseases [see sidebar].
The planning and management of timelines are key to successfully running a seasonal clinical trial. This includes from drafting
the study design through document submissions and patient recruitment, to the trial itself. Teams employed must be focused,
efficient, and resourceful, as well as fully trained in the indication studied and its seasonality.
This section focuses largely on the discussion of infectious diseases. Ultimately, noninfectious diseases such as seasonal
allergies are much more predictable, and the principles discussed here can be easily applied. However, the challenges arise
when dealing with infectious diseases where seasonality can be much more volatile and where trial management must be both
robust and flexible.
Regional profiles also need to be applied when managing the global trial. Standard geography subdivides the earth into regions
by latitude and there are seasonal disease fluctuations between these regions. Data for seasonal influenza, for example, can
be accessed from the World Health Organization's (WHO) FluNet site, which collates global influenza data for the purpose of
disease information and forecasting.
Top 5 Seasonal Diseases in Brief