This a case of one filter. This MERV Practical Pleat filter is 77% efficient airborne pathogens below 1.0 micron. The typical virus ranges from 0.01-0.2 micron in size, although they may cluster or attach to larger particles. Plus the Practical Pleat uses a self sealing gasket to maximize air filtration. The Practical Pleat used with a germicidal uv light is a great combination to improve your indoor air quality.