The emergence of novel pathogens, bacterial or viral, has always posed serious challenges to public health around the globe.
One of these dangerous pathogens is “severe acute respiratory syndrome coronavirus 2” or SARS-CoV-2, more commonly known for causing coronavirus disease 2019 or COVID-19, which was declared a global pandemic by the World Health Organization in early 2020.
Since its discovery in December 2019 in Wuhan, there have been over three million confirmed cases worldwide by April 2020.
With cases increasing exponentially around the world, it has caused significant burden on all aspects of society despite aggressive isolation methods to prevent the spread of the virus. Currently, therapeutic strategies to deal with COVID-19 are only supportive, making prevention aimed at reducing transmission the best method currently available.
One of the many ways implemented to prevent the spread of this virus, as with previous contagious pathogens, is frequent and effective handwashing. In both healthcare and community settings, alcohol-based hand sanitizers have become a popular alternative to the traditional handwashing with soap and water.
Alcohol-based hand sanitizers have been utilized as an effective alternative to handwashing to prevent the spread of bacterial and viral infections, making it one of the essential protocols in decreasing healthcare burden.
Let’s take a look at the efficacy of various types of alcohol-based hand sanitizers in eliminating bacterial and viral pathogens with the focus on the effectiveness against enveloped viruses, such as SARS-CoV-2.
Alcohol-based hand sanitizers
Hand sanitizer preparations containing alcohol on the other hand can include ethanol, isopropyl alcohol, n-propanol, or a combination of these, water, as well as excipients and humectants. Solutions containing alcohols between 60% and 95% in volume are most prevalent and effective.
Alcohol mechanism of action against bacteria
The compound, n-propanol, is the most commonly used alcohol compound in biocides. It is not known with much confidence the exact mechanism of alcohol’s antimicrobial activity, however, it may be related membrane damage, and inhibition or uncoupling of mRNA and protein synthesis through effects on ribosomes and RNA polymerase, or associated with protein denaturation. For activity against bacteria, its optimal bactericidal efficacy is achieved at concentrations between 60% and 90%.
Alcohol mechanism of action against viruses
The viral targets of alcohol-based hand sanitizers are predominantly the viral envelope, if present, which is derived from host lipid envelopes, the protein capsid, which contains and protects the genetic material, and the genetic material itself. Given that all these components are necessary for the viral life cycle (e.g., attachment, penetration, biosynthesis, maturation, lysis), and thus critical for its ability to transmit to another host, it can be presumed that altering the structure or function of any of the aforementioned components will typically render the virus ineffective.
While less is known regarding the specific mechanism of action of alcohols agents against viruses compared to bacteria, it is understood that ethanols have a broader and stronger virucidal activity than propanols.
Efficacy of hand sanitizers
Bacteria and fungi
Traditionally, bacteria on hands can be categorized as resident and transient floras. Common resident floras include Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis, which colonize deep layers of the skin and are resistant to mechanical removal. On the other hand, transient floras such as S. aureus, Escherichia coli, and Pseudomonas aeruginosa, colonize the superficial layers of skin. There are also numerous bacterial strains that can be transmitted to the host from other sources that can potentially develop into a variety of bacterial infections.
Alcohol-based hand sanitizers are very effective for:
Although viruses are more difficult to directly study in vivo compared to bacteria, numerous studies have attempted to validate the effectiveness of hand sanitizers on viruses.
Fig: Effect of Sterillium against infective murine norovirus (MNV1) (1% stool) after 30 s rubbing of the hands (N = 12). The infective virus was detected on five out of 12 finger pads. Different letters in x-axis represent different volunteers. Control is the recovery after 10 min drying on the finger pad. Horizontal line shows detection limit. Ref: https://pubmed.ncbi.nlm.nih.gov/25936671/
In low-resource settings; alternative hygiene options, such as hand sanitizer, could improve handwashing promotion to reduce influenza virus infections. A recent study conducted a cluster randomized control trial in 24 primary schools in Dhaka to assess the effectiveness of hand sanitizer and a respiratory hygiene education intervention in reducing influenza-like illness (ILI) and laboratory-confirmed influenza during June–September 2015. The incidence of laboratory-confirmed influenza was 53% lower in the intervention schools than in the control schools.
Fig: Number of influenza-like illness (ILI) episodes by week and study group in Dhaka, Bangladesh, June–September 2015 (N = 10,855). Note: Schools were on vacation from the 3rd week of June through the 3rd week of July 2015. Ref: https://pubmed.ncbi.nlm.nih.gov/31701861/
A very recent study evaluated a gel and a foam hand sanitizer that are commercially available in U.S. healthcare settings against SARS-CoV-2. To our knowledge, this is the first study to demonstrate inactivation of the SARS-CoV-2 by commercial formulated alcohol-based hand sanitizers marketed in the U.S.
These results are not surprising based on previous studies demonstrating the activity of ethanol against strains of coronavirus and formulated hand sanitizers against other enveloped viruses. These data support CDC recommendations to use alcohol-based hand sanitizer during the COVID-19 pandemic as the primary means for hand hygiene in healthcare settings; and as an option for the general public when soap and water are not convenient.
To summarize all the available evidence; it seems that soap and water is superior to sanitizer.
When handwashing is unavailable or inconvenient, a sufficient volume of sanitizer is important to ensure complete hand coverage, and compliance is critical for appropriate hand hygiene. Following the extrapolation of the virucidal data on viruses of similar structure to SARS-CoV-2, this virus can be effectively inactivated with current hand sanitizer products, though future research should attempt to determine this directly.
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