Vercelli studies the interaction of genetic and environmental factors in the development of allergic diseases, and her investigations have had a profound impact on the public's understanding of the development of asthma and allergic diseases.

In a highly acclaimed and influential experiment, the results of which were published in the New England Journal of Medicine, Vercelli and colleagues used a natural setting to demonstrate that the more children and their mothers played with and were exposed to farm animals, the fewer asthmatic symptoms the children displayed in later life. Comparing the allergy history of children raised in the Amish tradition in Indiana – where children and their mothers were exposed to horses and domestic animals on a daily basis – with families of Hutterites in South Dakota – whose farming practices were more structured and for whom daily contact with animals was much less – the researchers demonstrated that even though both populations had similar genetic backgrounds and lifestyles, the asthma and allergy symptoms of those in the former group were significantly lower than those of the latter.

Her research has led to several major prizes, grant funding totaling more than $40 million and national and international accolades. In 2010, she was elected to the Association of American Physicians. In 2018, she was elected secretary general of the Collegium Internationale Allergologicom – an international group that examines the scientific and clinical problems in allergy and related branches of medicine and immunology.