Up until 2003, the world had only ever seen four human coronaviruses (HCoVs). In just 20 years, three new HCoVs emerged: SARS, MERS, & SARS2.

The original four HCoVs were mild. They cause "the common cold" (along with some other viruses). The new HCoVs are killers. Mortality rate of SARS 9.4%. Mortality rate of MERS 34.4%. Mortality rate of SARS2 is evolving & age-dependent. ~30 million ppl have died already.

The original four HCoVs cause symptoms for 1 to 2 weeks. The new HCoVs often cause significant post-infection sequelae. Long SARS, Long MERS, & Long CoVID can last months, years or even a lifetime.

The original four HCoVs are seasonal. They typically infect ppl in winter months. The new HCoVs are NOT seasonal. They can infect in any season.

The original four HCoVs have a low rate of transmission, R0 ~ 1 to 2. The new HCoVs have a high rate of transmission. SARS2 in particular started higher, ~2.3 to 3.4, & has been rapidly increasing transmissibility. By 2022 it was already estimated to have an R0 ~ 18.6.

Explosive human growth & encroachment on animal habitats as well as proliferation of BSL3 & 4 labs & GoF research are two plausible reasons for the eruption of new & deadly HCoVs. Both are likely to continue. And so is emergence of new HCoVs.

One new HCoV? Hmm, OK. Two new HCoVs? That's more than coincidence. Three new HCoVs? That's a trend. A very disturbing trend.

When will the 4th new HCoV emerge? Some ppl suggest it already has because SARS2 has mutated so far from Wild Type it could be called SARS3. If not now, it soon will emerge as there are over 1,000 variants being tracked now and the pace of evolution is quickening.

When will the next HCoV make the jump from nature or leak from a lab? That's also likely not too far behind. This isn't over. In fact it's just beginning. #DavosSafe #WearARespirator

PS - The original four HCoVs could be stopped with surgical masks. The new HCoVs, especially SARS2, can't be. Higher level of transmission requires a higher level of respiratory protection. #WearARespirator