Acute allergic reactions occurred in 2.10% but anaphylaxis in only 0.025% of employees of two Boston hospitals who received their first dose of the Pfizer-BioNTech or Moderna COVID-19 vaccine, according to a research letter published yesterday in JAMA. Scientists from Massachusetts General Hospital and Brigham and Women’s Hospital administered email, text, phone, and smartphone app survey links to 64,900 employees who received a dose of one of the two mRNA coronavirus vaccines from Dec 16, 2020, to Feb 12, 2021. mRNA vaccines “teach” human cells to make a harmless part of the SARS-CoV-2 spike protein to trigger an immune response to the virus. The authors noted that people with a history of life-threatening reactions, or anaphylaxis, to allergens such as those in a vaccine are often hesitant to receive vaccines, which may complicate efforts to end the pandemic.