Social media posts mislead on filtration efficiency labels of face masks

"New knowledge! Masks without VFE cannot protect against virus," reads a Thai-language Facebook post from July 27 shared more than 3,000 times before it was deleted.

"No wonder some people still get infected even if they wear masks. When you buy a mask, check the side of the box."

The post -- which shows various photos of boxes of face masks -- claims that only masks with "VFE 99" printed on the box "can protect against the virus". 

"VFE" refers to virus filtration efficiency calculates the percentage of viral material that is blocked by a mask. 

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Screenshot of the misleading Facebook post, taken on August 4, 2021

A similar claim was also shared in Facebook posts here, here and here.

However, the posts are misleading.

Masks filter particles

"The claim that the filtration efficiency label needs to be 99 is unnecessary," Dr. Surachoke Tangwiwat, Deputy Secretary of Thailand's Food and Drug Administration, told AFP.

"Masks approved by the FDA, including medical masks and surgical masks, contain three layers of filtration to prevent particles from seeping through," he said.

"These masks are designed for medical use in preventing infections. Although they are not designed specifically for the virus, they filter out droplets and particles, and the virus bound in these particles."

The Thai public health ministry said in this report from July 2020 that "the COVID-19 virus looks like a spherical particle with a size of 0.06-0.14 microns that can pass through the holes of sanitary masks. But normally, this tiny virus will reside in droplets of patients which has the size of approximately 3.5-10.0 microns, so it can be filtered by with the surgical mask."

Proper fit important

Dr. Kajornsak Kaewcharat, Deputy Director-General of the Thai health ministry's Department of Disease Control said medical and surgical masks are effective against Covid-19 when worn properly.

"What’s generally overlooked is the correct use," he told AFP. "You need to wear the face mask properly."

The World Health Organization stressed the importance of wearing a mask correctly in this video.

"No matter how good your mask is at filtering the virus, if it doesn't fit, it doesn't work," the WHO said. "Look for masks that come in different sizes and find the one that fits your face."