The study is looking at systemic allergic reactions - which occur in one or more parts of the body beyond the injection site – and whether these are more frequent in the above groups than the general population.
It will also seek to understand the biological mechanism behind the reactions, and whether other factors (such as genetics) can predict who is at most risk.
Current FDA advice says that people who have had a severe allergic reaction to any of the ingredients of the Pfizer or Moderna vaccines should not receive them (neither should people have a second dose if they had a severe allergic reaction to the first dose).
It also advises people to talk to their vaccination provider if they have any allergies.
Weighing up risks and benefits
Moderna and Pfizer’s COVID-19 vaccines have both been authorized for emergency use in the US since December. Around 171 million doses of COVID-19 vaccines have been administered in the country to date (the vast majority from these two vaccines).
Most of the rare occurrences of severe allergic reactions has been limited to people with a history of allergies. These reactions have included anaphylaxis.
“The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech COVID-19 vaccines,” said Anthony S. Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
“The information gathered during this trial will help doctors advise people who are highly allergic or have a mast cell disorder about the risks and benefits of receiving these two vaccines.
“However, for most people, the benefits of COVID-19 vaccination far outweigh the risks.”
The Phase 2 trial, called Systemic Allergic Reactions to SARS-CoV-2 Vaccination, is sponsored and funded by NIAID. The study team will enroll 3,400 adults aged 18 - 69 at 35 academic allergy-research centers across the US.
Mast cell disorder is caused by abnormal or overly active mast cells (a type of white blood cell): predisposing a person to life-threatening reactions that look like allergic reactions.
Around 60% of study participants will have either a history of severe allergic reactions (such as to food, insects stings or vaccines/drugs) or a diagnosis of a mast cell disorder, while the remainder will not.
Approximately two-thirds of participants in each group will be female, because severe allergic reactions to vaccines in general ― and to the Moderna and Pfizer-BioNTech COVID-19 vaccines in particular ― have occurred mainly in women.
The site investigators are allergists trained to recognize and treat anaphylaxis. Emergency medications, oxygen and medical equipment will be on hand to treat allergic reactions as needed. Participants will be observed for at least 90 minutes after each injection in case any type of reaction occurs.
Results from the study are expected in late summer 2021.
