An itchy rash may be a side effect of receiving the Moderna vaccine, doctors said. About 12 recipients in a 30,000-person trial have seen their arms turn red, sore, itchy or swollen about a week after receiving the first dose, according to a letter from doctors published Wednesday in the New England Journal of Medicine. Five of the patients had large skin lesions more than 10 centimeters (4 inches) in diameter at the injection site, the letter said. Two experienced the rash in other places, such as near the elbow and on the palm of the hand.