For immunity, consuming a variety of fresh produce in different colors is very important. Also, I would recommend a probiotic supplement, as healthy gut is associated with stronger immunity.
If you have access to practitioners who do moxa (a heat therapy by burning dried mugwort wool near certain acupressure points to build stronger immunity or treat other conditions), it is a great time to do that. In Chinese is called 艾灸 .
Alternatively you can also purchase good quality dried mugwort leaves, and do a foot soak in the evenings. For that, take 60 grams of the dried leaves, add 1 – 1.5 litres of water and boil for 20 minutes to get a tea. Let it cool and use that ‘tea’ as your foot soak.