Should I Be Wearing an N95 or KN95? Understanding the Evolving Advice on Masks

(Bloomberg) -- Advice from U.S. authorities on the need for face masks has flipped back and forth since Covid-19 took hold in 2020. In May, the Centers for Disease Control and Prevention said immunized Americans could ditch their masks in most settings. It reversed course in July amid a rise in cases caused by the more transmissible delta variant. Now, with the quickly spreading omicron variant causing a surge in infections, the agency is urging wider use of medical-grade masks in the general public. It revised earlier guidelines that had discouraged the use of gold-standard N95 masks in order to reserve them for medical workers. 

1. What’s the current advice?

The CDC’s recommendations on when to mask, last updated in October before the omicron variant emerged, say that people age 2 and older who are not fully vaccinated should mask in indoor public places. Those who are fully vaccinated, the agency says, should mask indoors in public where rates of transmission of the virus are substantial or high. Masking is mandatory on public transportation in the U.S. and in transportation hubs such as airports and train stations. The CDC advised Jan. 14 that “you wear the most protective mask you can that fits well and that you will wear consistently” and said that properly fitted masks of the N95 variety provide the highest level of protection.

2. What are N95 masks?

Medical masks, which are regulated devices, come in two types. Surgical masks are the loose-fitting, one-size-fits-all kind that are rectangular when flat. A more sophisticated medical mask is called a respirator. In the U.S., the most commonly available versions are called N95s and KN95s; in Europe, these are called FFP2s. Respirators are meant to form a tight seal against the face. That forces the user to pull air through the device’s filter rather than through gaps on the sides. They are designed to keep out not only respiratory droplets, but also smaller aerosol particles that can carry infectious agents and float for a time through the air. Apart from medical professionals, respirators are also often worn by tradespeople such as painters to protect them from airborne toxins.

3. What’s the difference between an N95 and a KN95?

The biggest difference between N95 and KN95 masks, which both filter out at least 95% of particles in the air, is where they are certified. KN95s are manufactured in China and thus are subject to different certification requirements than U.S.-made N95s. In China, KN95 manufacturers must run a “fit test” on real humans to ensure the masks allow little to no leakage. Makers of N95s aren’t required to run that test but must still meet standards set by the National Institute for Occupational Safety and Health. The CDC estimates that about 60% of KN95s in the U.S. are fakes, that is, counterfeits made to look as if they came from legitimate manufacturers in China, and don’t meet NIOSH requirements. 

4. What’s the evidence for using respirators?

Cloth masks only block 10% to 30% of aerosol-sized particles, according to Ashley Styczynski, an infectious disease fellow at Stanford University. The U.S. Food and Drug Administration has said surgical masks are effective at protecting against splashes and large-particle droplets but not the small particles that may be transmitted through a cough or sneeze. A study from Germany’s Max Planck Institute found that tight-fitting FFP2s provide 75 times better protection against a coronavirus infection than a surgical mask. False claims that coronavirus particles are too small for N95 masks to be effective were addressed by the U.S. Occupational Safety and Health Administration, which said that when virus particles are expelled through a cough or sneeze, they are attached to water and mucus, slightly increasing their size. Those particles are easily trapped and filtered by respirators. All masks are most effective when tight-fitting and worn properly around the nose and mouth. 

5. Are there any downsides?

Respirators are uncomfortable to wear for a long period of time. They retain heat and exert pressure on the face, and some people find they make it difficult to breathe, which can make them unsuitable for those with cardiac and respiratory conditions. The cost of respirators, which generally sell for $1 to $2 more per mask than a surgical one, can make them inaccessible to some people. Some local governments, in Chicago for example, have begun to distribute respirators to residents at no cost. But there’s often a restriction on how many each person can get, making it a limited solution. 

6. What weight does CDC guidance carry?

The CDC guidance is exactly that: guidance. Adoption and enforcement of its advice is up to state and local governments, employers and local businesses.

The Reference Shelf

• Related QuickTakes on the omicron variant, coronavirus plus flu, vaccine mandates, how omicron is affecting the performance of coronavirus tests and Covid treatments, and flying amid the omicron surge.
• The CDC’s mask guidance.
• Bloomberg Opinion sorts through the evidence on masking.

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