WHO-guided hand rub formulations effective against coronavirus
Both alcohol-based hand rub formulations recommended by the WHO* are effective against SARS-Cov-2 when used correctly, a new study shows — supporting their use in healthcare settings and viral outbreaks.
“To limit virus spread, effective hand hygiene is crucial,” the researchers stated. “The WHO’s recommendations are based on fast-acting, broad-spectrum microbicidal activity, along with accessibility and safety.”
The two formulations originally recommended by the WHO contain either 80% (vol/vol) ethanol (formulation I) or 75% (vol/vol) isopropanol (formulation II), in addition to 1.45% (vol/vol) glycerol and 0.125% (vol/vol) hydrogen peroxide for both. [Emerg Infect Dis 2020;doi:10.3201/eid2607.200915]
Both formulations I and II effectively inactivated SARS-Cov-2 by a reduction factor (RF) of ≥3.8.
The researchers found similar results when the content of the alcohol was modified to weight-based rather than volume-based formulation. For the modified versions, formulation I contained 80% (weight/weight) ethanol (which is equivalent to 85.5% [vol/vol]), while formulation II contained 75% (weight/weight) isopropanol. Glycerol content was adjusted accordingly to 0.725% (vol/vol) for both.
Again, both the modified formulations resulted in viral inactivation by an RF of ≥5.9.
“Of note, both the original and modified formulations were able to reduce viral titres to background level within 30 seconds,” said the researchers.
Also, regression analyses of both the modified formulations showed similar inactivation profiles for other types of coronaviruses, including MERS-CoV, SARS-CoV, and BCoV.
30 seconds rule
For the study, the researchers conducted virucidal activity test by exposing SARS-Cov-2 to the disinfectant formulations for 30 seconds in vitro. The samples were then serially diluted and tested for cytotoxic effects using crystal violet staining.
“This time frame [30 seconds] was chosen based on recommendations for hand disinfectants,” explained principal investigator Dr Stephanie Pfänder of Ruhr University Bochum in Bochum, Germany.
“Alcohol constitutes the basis for many hand rubs routinely used in healthcare settings,” the researchers pointed out. As such, they also tested the active ingredients — ethanol and isopropanol — against SARS-Cov-2 at full strength and multiple dilutions.
The researchers found that both ethanol and isopropanol completely inactivated the virus in 30 seconds, and that a concentration of ≥30% (vol/vol) alcohol was sufficient.
“We showed that both WHO-recommended formulations sufficiently inactivate the virus after 30 seconds,” Pfänder concluded.
“[However,] one caveat of this study is the defined inactivation time of exactly 30 seconds, which is the time recommended but not routinely performed in practice,” cautioned Pfänder and co-authors.
*WHO: World Health Organization