The US National Institutes of Health (NIH) has begun a Phase II clinical trial to analyse whether highly allergic individuals or those with mast cell disorder are at greater risk for an immediate, systemic allergic reaction to the Moderna or Pfizer-BioNTech Covid-19 vaccines.

The vaccines of these companies are currently authorised by the Food and Drug Administration for emergency use.

Named ‘Systemic Allergic Reactions to SARS-CoV-2 Vaccination’, the trial is sponsored and funded by the NIH unit National Institute of Allergy and Infectious Diseases (NIAID).

The study will enrol 3,400 adult subjects aged 18 to 69 at up to 35 academic allergy-research centres in the country.

Trial subjects will be randomised to receive either the Pfizer-BioNTech vaccine (one-third of them), the Moderna vaccine (one third), a placebo followed by the Pfizer-BioNTech vaccine (one-sixth), or a placebo followed by the Moderna vaccine (one-sixth).

The proportion of subjects in each group with a systemic allergic reaction 90 minutes after receiving either of the vaccines will be evaluated by the investigators, with results anticipated in September this year.

NIAID director Anthony Fauci said: “The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech Covid-19 vaccines.

“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.”

Meanwhile, Moderna has reported antibody persistence data at six months following the second dose of its Covid-19 vaccine.

The study assessed 33 healthy adults in the NIH-led Phase I study of the Moderna COVID-19 Vaccine at six months following the second 100μg dose.

Data showed that antibodies elicited by the vaccine persisted until six months after the second dose.

Moderna noted that the studies analysing immune responses over six months are progressing.

Last week, the NIH initiated dosing in a new Phase I clinical trial of Moderna’s investigational vaccine candidate, mRNA-1273.351, in adult subjects.