“Worn as designed, both commercial surgical masks and cloth masks had widely varying effectiveness (53 – 75 percent and 28 – 91 percent particle removal efficiency, respectively)”. Different brand, different results and only when they applied “nylon layers” did the “efficiency” improve. Synthetic fibres do not breathe, so this will inevitably effect your breathing.
Study article: https://pubmed.ncbi.nlm.nih.gov/32838296/ Lifesite
"As the number of infected cases has just become too big, this allowed the novel coronavirus more opportunities to mutate and select. New variants will continue to emerge," said Shi, whose lab was working with a US-Funded nonprofit to make bat coronaviruses more infectious to humans.....she doesn't discuss how much more or less deadly new strains could be.
For example, there's no evidence that the Delta strain - while much more virulent than the original Alpha strain of Covid-19, is any deadlier.
"There's no evidence that it's more deadly," said Dr. Larry Corey, who is coordinating all of the COVID-19 vaccine research in the U.S (via King5). "There is evidence that it's more infectious and more infectious to others, i.e., more transmissible. But [is it] actually more severe? There's really not good hard evidence of that."
"Becoming more transmissible and less lethal are absolutely what’s best for the pathogen," said Troy Day, a professor of mathematics and biology at Queen's University in Canada, who has studied how infectious diseases - including coronaviruses - evolve (via AP).
That said, sometimes viruses become more deadly.
"...in many instances is never possible, to be more transmissible and also less lethal," Day added - noting that there are documented cases of animal viruses which have evolved to become more lethal over time.
Some examples of viruses that became more deadly over time include those that developed drug resistant variants, and animal viruses such as bird flu, which were harmless to humans initially but then mutated to become capable of killing people, according to Dr. Amesh Adalja, a senior scholar at Johns Hopkins University’s Center for Health Security.
"Flu viruses have developed resistance to certain antivirals that make them more difficult to treat, and therefore make them more deadly," said Adalja, noting that this has happened with HIV and certain strains of Hepatitis C." ZeroHedge