HONG KONG—A new generation of Covid-19 vaccines that can be inhaled or sprayed up the nose—instead of taken by injection—will begin rolling out in Asia, though just how effective they are remains to be seen. Regulators in China and India have greenlighted distribution of vaccines delivered through the mouth or nose, a delivery that scientists say holds the promise of more potent protection against Covid-19 by better reducing infections and preventing the disease’s spread among vaccinated people because they work in the nose and lungs where transmission first happens.

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