Disease doesn’t distinguish between friend and stranger. Just because you like someone doesn’t mean they can’t infect you with COVID-19 or the flu or any other contagion nature can conjure. A virus is ruthlessly indifferent about your social circle.

That isn’t, however, what the human brain believes.

A recent study by Spanish researchers shows that people often lapse into a false sense that they are less likely to be infected by friends during the coronavirus pandemic. And because we feel less vulnerable, we take fewer precautions.

The irony, of course, is that increases the chances of contracting COVID-19.

Researchers tested the phenomena known as the “friend-shield effect” in a number of online experiments. In one, nearly 500 participants were split into two groups. All were asked to write a few observations about either a friend or an acquaintance. Afterward, they read a statement suggesting junk food increased the odds of getting a severe case of COVID-19. Subjects were then given an offer in an online store where they could buy either chocolate and chips or face masks, disinfecting wipes and sanitizer.

Investigators found folks were more likely to buy junk food after writing about  friends, compared with the group that wrote about acquaintances.

Scientists note the friend-shield effect can also be seen in like-minded groups. For example, fans of the same baseball team might implicitly trust other supporters as being virus-free as they gather in a sports bar to watch a game.

So, keep your guard up. A hitchhiking virus isn’t checking your Facebook account. Anyone can transmit the coronavirus, friend and foe alike.