Modified ISO 21702 Measurement of Antiviral Activity

Summary of Microchem’s Modified ISO 21702 Method-Measurement of Antiviral Activity on Plastics and Other Non-porous Surfaces

• The test virus is propagated, titrated, and stored under ultra-low conditions. The method suggests testing against two viruses: Influenza virus, a large enveloped virus; and Feline calicivirus, a small non-enveloped virus. Microchem Laboratory offers a wide range of Influenza sub-types and strains in our library.
• On the day of testing, virus is removed from its ultra-low freeze, diluted if required, and supplemented with soil if the Study Sponsor requested a soil load. If no soil load is requested, the virus is tested as propagated (i.e., Feline calicivirus in 2% Fetal Bovine Serum [FBS] and Influenza Virus in 0% FBS).
• Test and control substances are inoculated with virus, overlayed with cover film and allowed to dwell for the contact time at the Study Sponsor’s requested temperature and humidity.
• Time zero controls are prepared, inoculated, and immediately harvested. Harvesting consists of removing the cover slip, washing the cover slip and sample surfaces with neutralizer. The suspension is collected and transferred to a sterile vessel or passed through a neutralization column, if needed.
  • All other controls (e.g., Verification of Cytotoxic Effect, Verification of Cell Sensitivity to Virus and the Inactivation of Antiviral Activity (Neutralization Verification)) are run in parallel with the test.
• At the end of the contact time, test and control substances are harvested as described above. Serial 10-fold dilutions are prepared from each suspension collected, and each dilution is inoculated in quadruplicate into indicator cells.
• At the end of incubation, viral titer is calculated for each parameter, and a log reduction is calculated for each sample tested. Log reductions are calculated by taking the viral titer recovered from parallel untreated control substances and subtracting it from the viral titer recovered from treated test substances. If multiple substances were tested, an average reduction is calculated.

Strengths of the ISO 21702 Test

• This method is quantitative and typically conducted in triplicate for each parameter of the study, easily demonstrating reproducibility.
• Specific success criteria, making determination of efficacy easy.

Weakness of the ISO 21702 Test

• The method suggests a 24-hour contact time with test and parallel control substances held at 25±1°C and ≥90% relative humidity, however a meaningful log reduction may be difficult due to natural virus inactivation over long periods of time.