They mean that because children aren't contracting HSV-1 from ordinary contamination and contact at early ages, as they typically do in developing countries, th

They mean that because children aren't contracting HSV-1 from ordinary contamination and contact at early ages, as they typically do in developing countries, they are more likely to contract it from oral sex later in life. My guess is that if you contract the virus in childhood, there is less risk of a genital infection later in life because the antibodies would already be present.