Neither of these things are guaranteed to happen if you get the flu vaccine when you are sick, but they are possibilities. If you have just a mild illness, there is no reason to wait to get vaccinated.
Early in the day, let roast stand at room temperature at least 1 hour before cooking. Preheat oven to 375 degrees. Rub meat ... the outside and rare in the middle. Meat will be very brown ... stand at room temperature for at least one hour.
Cover the clay pot with the lid and place the pot into a cold oven. Turn the oven to 475 degrees F and bake the roast for 90 minutes, or until a meat thermometer inserted into the center of the roast reads 170 degrees F.