The added value of adequate immune fitness to the existing approaches to pandemic preparedness

In a recent review published in the Journal of Clinical Medicineresearchers described two studies, the CLOFIT (Corona lockdown: how fit are you?) retrospective study and the COTEST (Corona test street) real-time study, that investigated if maintaining adequate immune fitness could significantly add to the current strategies of preparedness for coronavirus disease 2019 (COVID-19) and other pandemics.

Image Credit: Pandemic Preparedness: The Importance of Adequate Immune Fitness. Image Credit: ImageFlow/Shutterstock


Adequate immune fitness refers to the intrinsic adaptability to challenging external health conditions by increasing the resiliency of the immune system for preventing or combating an infection. It is essential to adopt healthy lifestyle habits such as the consumption of a balanced diet, physical exercise, and refrain from smoking, drugs, or alcohol use to improve the immune fitness for robust protection against infection by pathogenic organisms.

The global strategy for preventing and mitigating COVID-19 has mainly focussed on the early diagnosis and the development of COVID-19 vaccines and drugs. However, COVID-19 therapeutics do not have uniform accessibility globally, especially for the low- and middle-income nations. Lifestyle changes offer a cost-effective, easily adoptable, and directly beneficial solution to upscale individual preparedness toward COVID-19 and future pandemics.

The CLOFIT study

The CLOFIT study was an online survey-based study comprising 1,415 adult Dutch individuals enrolled via Facebook advertisements. The study assessed their pre-pandemic immune fitness (2019) during the first COVID-19 lockdown period between March 15 and May 11, 2020 (during which the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Alpha variant was predominant).

Besides demographics, the individuals reported the following: their perceived immune fitness in the previous year [immune fitness (2019)]; their perceived immune fitness in the initial lockdown [immune fitness (DL)]; and the number and severity of COVID-19 symptomatology in the lockdown.

Nine symptoms associated with the Alpha variant were assessed, which were: runny nose, sneezing, coughing, sore throat, dyspnea, malaise, elevated temperature (up to 38 C), fever (above 38 C), and chest pain.

Based on the step-wise regression analysis, the immune fitness (DL), immune fitness (2019), and the presence of underlying diseases significantly correlated with the number and severity of COVID-19 symptoms. However, immune fitness (2019) was the most important predictor of the number and severity of COVID-19 symptoms.

The immune fitness variables (DL and 2019) were substantially lower among women than men, with a substantially greater number of symptoms and increased COVID-19 severity reported by women. The patient’s age and body mass index (BMI) were weakly correlated with the presence and severity of COVID-19 symptomatology.

The COTEST study

The COTEST study was a real-time study conducted between December 2020 and June 2021 (during which the SARS-CoV-2 Delta variant was predominant) on 925 Dutch adults tested for SARS-CoV-2 by rapid antigen tests. The test results were sent via email, which also contained a survey to be filled out online for participating in the study.

The survey comprised an assessment of the individual’s demographics (sex, age, height, bodyweight) to derive the BMI values. Additionally, underlying medical disorders viz. cardiovascular disorders and hypertension, hepatic disorders, renal disorders, diabetes, neurological disorders (eg, migraine , epilepsy), immunological conditions (eg, Crohn’s disease, rheumatism), respiratory disorders (eg, asthma, chronic obstructive pulmonary disease), psychological disorders (eg, depression, anxiety) and allergic conditions (eg, hay fever) were reported.

Seventeen symptoms observed in Delta infections were assessed, which were: sore throat, runny nose, coughing, dyspnea, fever (≥ 38 C), chest pain, headaches, congestion, shivering, fatigue, ageusia, anosmia, muscle pain, confusion, blueish face or lips, difficulty in waking up or staying awake, diarrhea, nausea, and vomiting.

Immune fitness (2019) was assessed using the seven-item immune status questionnaire (ISQ), which included diarrhea, common cold, sudden elevation in body temperature, headaches, musculoskeletal pain, dermatological problems (eg, eczema and acne), and coughing. The perceived immune fitness at the time of testing [immune fitness (T)] was assessed loss with a one-item scale.

In the COTEST study, the immune fitness variables (T and 2019) significantly correlated with the number and severity of COVID-19 symptoms in SARS-CoV-2-positive and SARS-CoV-2-negative individuals, confirming the findings of the CLOFIT study. However, among SARS-CoV-2-positive individuals, the immune fitness (2019) was the only robust predictor of the number (27%) and severity (33%) of COVID-19 symptoms during the pandemic.


The findings of the CLOFIT study and the COTEST study showed that adequate immune fitness is associated with substantially fewer and less severe COVID-19 symptoms. In addition to early SARS-CoV-2 detection and COVID-19 vaccines and other therapeutics, measures taken to Maintaining adequate immune fitness, such as lifestyle changes supported by increased government healthcare investments, are vital for improving the global preparedness for COVID-19 and future pandemics.


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