And even that particular strain of coronavirus which leads to COVID-19 has continuously mutated itself over the course of the past year and a half. What that means for the public is that, depending on which version of the coronavirus you may catch, the tell-tale symptoms may diverge. But it’s not always clear exactly how. Classic COVID may start off with loss of smell or taste; catching the COVID Delta strain may not lead to those symptoms but could cause others such as a runny nose and headache.

COVID is a strange puzzle of a disease which public health officials are still trying to piece together. The most common, and some of the weirder, symptoms have been on the radar for a while now: A sudden loss of taste or smell, sore throat, runny nose and congestion, nausea, diarrhea, difficulty breathing, fever, muscle aches. The typical trappings of something like the flu crossed with the cold and then multiplied by unexpected symptoms such as sensory dilution and the dire prospect of having to live with them if you have a case of “long COVID.”

The multiple COVID variants now circulating the globe, include the Delta variant which now makes up a majority of new COVID-19 cases in the U.S., complicate the matter further since different variants may manifest in different ways. And all of these mutations, whether they be the Alpha, Delta, or Lambda variants or something else entirely, are still so new that it’s difficult to assess the precise nature of each individual threat.

Of the major mutation groups that the Centers for Disease Control (CDC) and the World Health Organization (WHO) list as “variants of concern,” the Delta variant is by far doing the most damage globally due to its transmissibility and high levels “viral load” that can spread the pathogen faster and at an earlier stage of illness.

For now, it appears that the Delta variant (even in some who are fully vaccinated for COVID) can cause symptoms such as a headache, sore throat, and runny nose, and also potentially a fever and a cough, based on recent data from the U.K., which is grappling with Delta variant breakouts. Those are all typical COVID symptoms generally but don’t include the tell-tale sign of taste or smell loss.

That means that as we head into the flu and cold season in several months, it might become more difficult to distinguish between a highly contagious COVID Delta variant patient and someone with a mild flu.

The coming years will reveal the breadth and depth of COVID-19 symptoms across its variants. For now, the good news is that while available vaccines from the likes of Pfizer and AstraZeneca may not entirely prevent coronavirus mutations from spreading, and these kinds of symptoms occurring, they are quite effective in preventing serious illness that can lead to hospitalization or death.