The only thing that can come to mind is maybe have the new one co sleep in a separate area if possible if not maybe you could stay with a family? with the newborn
It happened to me, I slept with the newborn in a different room, or living area. I washed my toddler hands constantly, I used an air purifier and disinfectant spray and wipes. My newborn ended up being just fine. And of course I didn’t let my toddler to be around him. It was sad but he understood..
If you are nursing, make sure you get the germs yourself so you can pass antibodies to your newborn ❤️
Air purifier, open the windows just a crack for fresh air circulation every hour for about 10 mins, cool most humidifier and keep them separated the best you can. Good luck! 🍀