The author of a recent New England Journal of Medicine study on the virus, Alimuddin I. Zumla, said he didn’t know the reason behind the gender difference, but then he offered the New York Times a guess:

“I don’t think the virus prefers any gender,” Dr. Zumla said, adding that he suspected that Saudi women might be protected by their veils, which cover their mouths and noses and might help keep the virus out.

Over at Discover, infectious disease specialist Rebecca Kreston pokes holes in that theory. The niqab, or face veil, doesn’t reduce the likelihood of catching respiratory infections, it seems:

In a 2001 study on the effect of the niqab veil on incidence of respiratory disease in Saudi women, researchers unexpectedly found that bronchial asthma and the common cold “were significantly more common in veils users;” wearing the veil may have contributed to dense, wet spots close to the mouth and nose which could faciliate the growth of organisms that lead to infection.

Indeed, in a 2006 study of respiratory infections during the Hajj, researchers did find that pilgrims were more likely to contract a virus when they stayed at the Hajj longer or when they prayed at particularly crowded mosques. They also found that while men at the Hajj could reduce the likelihood of infection by wearing a protective face mask, that didn’t hold true for women and their niqabs. (However, the authors note that women sometimes take off their veils when inside and in the presence of other women, so it’s not a perfect proxy for a facemask, which is worn more consistently.)

The NEJM study on MERS found that 50 percent of female cases in hospitals were infected by other women within their gender-segregated wards. But there’s still a lot we don’t know about the patients and what they did before they died. Kreston raises a few questions:

Were infected woman convalescing in hospital wards wearing their niqabs and the abaya robe that cover the length of their body, which may have reduced their exposure to MERS within the hospital environment? Was it the case that the niqab protected women from infection or because they have inflexible, highly structured and segregated relations with men which negated any possibility of exposure?

It could be that purdah, the system in which men and women in conservative Muslim countries like Saudi Arabia live separate lives, somehow prevented women from coming into contact with infected men. Describing a Riyadh household where four men fell ill with the virus but none of their female care-takers did, researchers previously noted that the men interacted with society far more than their spouses and daughters did:

“All adult and adolescent male family members shared meals together and ate separately from female relations and their young children. The men also socialized and visited the local mosque together.” 

Or it could also be that women are less likely, for either cultural or economic reasons, to access health care, or to work as health care providers.

So far, the CDC hasn’t advocated calling off plans to travel to the Middle East or to Saudi Arabia, and the agency advises travelers to simply wash their hands and avoid sick people. But it will be interesting to see if the particular customs of Saudi Arabia somehow either hastens or slows the spread of what could be the new global pandemic. Or maybe the WHO will advise female pilgrims to pull face-masks over their niqabs.

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