Neem is the most powerful anti-viral medicine practiced in India in the history of all epidemics. In cholera/plague, malaria, measles, small pox, chickenpox, flues etc. Neem is used as preventive and curative drug.
Arka is the most powerful form of Ayurvedic medicine in which the real active ingredient of medicine is collected as distillate. Nimbarka is indicated for jwara (fever) with kasa (cough & breath difficulties), srama (tiredness) along with krimi (attack of microbes).
It is noted that Neem is heated more its anti-microbe activity will decrease, hence kwatha (decoction), Arishta, extracts, tablets & capsules won’t give much result in anti-microbe action. Hence Arka is the most potent form in which direct medicinal vapors are condensed, so anti-viral potency is more in the form.