Pandemics, such as COVID-19, are probably more likely than before. We are with more, we increasingly live in megacities, and we travel vastly more. We also have large quantities of animals for feeding us, where diseases can be created and transferred to us. On the other hand, we have better hygiene, medicine, information, and coordination. But the balance could be negative. Even for diseases originating in nature, the threat level we currently face is largely man-made.
Pandemics such as COVID-19 have a relatively low mortality rate. And even though there are natural pandemics with much higher mortalities, the most prominent existential risk does not come from natural diseases.
Pandemics which are engineered on purpose pose a higher existential risk than natural ones. From the first creation of genetically modified bacteria in 1973, we have steadily increased our ability to create transmissible deadly diseases. The main candidate for existential risk for the next hundred years stems from our technology.