We've spent some time researching the impact of yoga on the immune system (very good by the way), and one key point is that there are several research papers that show that the use of nasal irrigation (through a special plastic pot from the pharmacy, or a neti pot, and a saline solution) can make a big difference to how many symptoms people get, and how long those symptoms stay. Some of the research involved Corona viruses (not Covid-19 as it is too new) and the results were promising.
For example, this very recent research from Edinburgh academics shows that nasal irrigation and gargling produced less severe Corona virus symptoms and shorter symptom times. For now New Zealand is in the clear with Covid-19, but this research may also be useful for dealing with colds and flu:
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