It pays to have a medical mask on hand during flu season.

New research reports finding “no significant difference in the effectiveness” of medical masks vs. N95 respirators for prevention of influenza or other viral respiratory illness.

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“This study showed there is no difference in incidence of viral respiratory transmission among health care workers wearing the two types of protection,” said Dr. Trish Perl, Chief of UT Southwestern’s Division of Infectious Diseases and Geographic Medicine and the report’s senior author.

“This finding is important from a public policy standpoint because it informs about what should be recommended and what kind of protective apparel should be kept available for outbreaks.”

Nurses, doctors, and other medical personnel who come into direct contact with patients are frequently exposed to contagious diseases such as influenza (flu). During large outbreaks (such as the H1N1 pandemic of 2009) as many as one in three healthcare workers could contract the disease they’re fighting against, says Dr. Perl.

During that pandemic, the U.S. Centers for Disease Control and Prevention (CDC) recommended the use of N95 respirators, designed to fit closely over the nose and mouth and filter at least 95% of airborne particles. The looser-fitting surgical masks routinely worn by healthcare workers were considered insufficient, Dr. Perl said, but there weren’t enough of N95 filters for every facility.

The new study came to follow-up on previous research comparing the masks and respirators, which yielded mixed results. The team used data from several Department of Veterans Affairs hospitals and multiple medical institutions in seven cities including Houston, Denver, Washington, and New York, collected with the help of multiple universities throughout the USA. The figures pertained to the four flu seasons between 2011 and 2015, examining the incidence of flu and acute respiratory illnesses in the almost 2,400 health care workers who completed the study.

The team reports that 207 laboratory-confirmed influenza infections occurred in the N95 groups versus 193 among medical mask wearers. In addition, they found 2,734 cases of influenza-like symptoms, laboratory-confirmed respiratory illnesses, and acute or laboratory-detected respiratory infections (where the worker may not have felt ill) in the N95 groups, compared with 3,039 such events among medical mask wearers.

“It was a huge and important study — the largest ever done on this issue in North America,” says Dr. Perl.

“The takeaway is that […] one type of protective equipment is not superior to the other,” she adds. “Facilities have several options to provide protection to their staff — which include surgical masks — and can feel that staff are protected from seasonal influenza. Our study supports that in the outpatient setting there was no difference between the tested protections.”

The team plans to investigate the dynamics of virus transmission in the future, in order to better understand how to protect medical personnel from them.

The paper “N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel” has been published in the journal JAMA.