The Immune Defence Study
Large-Scale Randomized Trial Provides Proof of Principle--Nasal Sprays Work on Demand but Must be Used Daily to Prevent Viral Upper Respiratory Infections Altogether
By Peter A. McCullough, MD, MPH
Nasal sprays and gargles are the most widely available and safest products we have to help prevent viral upper respiratory tract infections. Viral particles stick in the anterior nose on the hair cells for about five days until they replicate to the point of invading the mucosal cells causing the characteristic symptoms of a cold. Because the lymphatics drain to the back of the throat, oftentimes a sore throat is the first sign of a viral infection in the nasal cavity. Many have said there are no large scale randomized trials of nasal sprays to prove the concept of prevention after sick exposure or in early treatment of a cold. Until now.
Little and colleagues published the Immune Defence Study in Lancet Respiratory Diseases in 2024.
This randomised, controlled, open-label, parallel-group trial was done at 332 general practitioner practices in the UK. Eligible adults (aged ≥18 years) had at least one comorbidity; obesity [BMI ≥30 kg/m2]; or age ≥65 years) or at least three self-reported respiratory tract infections in a normal year (ie, any year before the COVID-19 pandemic). Participants were randomly assigned (1:1:1:1) to: usual care (brief advice about managing illness); Vicks First Defence gel-based spray or a saline nasal spray (two sprays per nostril at the first sign of an infection or after potential exposure to infection, up to 6 times per day); or a brief behavioural intervention in which participants were given access to a website promoting physical activity and stress management. Between Dec 12, 2020, and April 7, 2023, of 19 475 individuals screened for eligibility, 13 799 participants were randomly assigned. Compared with participants in the usual care group, who had a mean of 8·2 (SD 16·1) days of illness, the number of days of illness was significantly lower in the gel-based spray group (mean 6·5 days [SD 12·8]; adjusted incidence rate ratio [IRR] 0·82 [99% CI 0·76-0·90]; p<0·0001) and the saline spray group (6·4 days [12·4]; 0·81 [0·74-0·88]; p<0·0001), but not in the group allocated to the behavioural website (7·4 days [14·7]; 0·97 [0·89-1·06]; p=0·46). Compared with usual care, antibiotic use was lower for all interventions: IRR 0·65 (95% CI 0·50-0·84; p=0·001) for the gel-based spray group; 0·69 (0·45-0·88; p=0·003) for the saline spray group; and 0·74 (0·57-0·94; p=0·02) for the behavioural website group.
This trial found on demand use of pharmacologically inactive nasal sprays (Vicks, saline) had an impact which is very difficult to show in a randomized trial using survey data outcomes. I have found clinically it is hard to determine sick exposures and even the onset of “coming down with a cold.” Thus the rationale for routine twice daily instead of on-demand nasal sprays is very strong. Using xylitol or povidone iodine based sprays and adding a throat spray and/or gargle is a big upgrade from Vicks polymer or saline. I have interviewed multiple individuals who have had zero colds in 2024—the common factor is the daily use of nasal sprays and gargles. I have learned the brand you choose is less important than committing to twice daily use—like flossing and brushing your teeth. Here are the two pairs I most commonly recommend.
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Peter A. McCullough, MD, MPH
President, McCullough Foundation
www.mcculloughfnd.org
Yes I agree, nasal sprays like providone mix or xclear appear to really make a difference. I use when traveling on planes or in large crowds- parties, funerals, church, weddings or at first sign of scratchy throat. That being said, I quickly do a preventive dose of ivermectin, D, C, zinc too. The combination really works. I just do not get sick anymore. I used to get sick after every flight and several colds a year. Not since doing this. Daily spray would be even better, but many days I work alone and outside. My husband refuses the nasal sprays and is on day 7 of a cold now...
Thank you, Dr. McCullough! Very helpful and reassuring.