Second Covid shot safe after allergic reactions to first dose: Study

An allergic reaction after the first mRNA Covid-19 vaccine dose scares people from taking the next shot. However, a new study has shown that the second shot is safe and does not present any complications.

A team of researchers, led by allergists at Massachusetts General Hospital (MGH) in the US, stressed that a first dose reaction to Covid-19 vaccination should not keep people from getting a second dose.

Allergic reactions after mRNA Covid-19 vaccinations have reported to be as high as 2 per cent. Anaphylaxis--a life-threatening whole-body allergic reaction--occurs in up to 2.5 per 10,000 people.

In the study, published in JAMA Internal Medicine, 32 patients(17 per cent) among 189, experienced anaphylaxis after their first dose of mRNA Covid-19 vaccine. A total of 159 patients (84 per cent) went on to receive a second dose.

All 159 patients, including 19 individuals who had experienced anaphylaxis following the first dose, tolerated the second dose.

Thirty two patients (20 per cent) reported immediate and potentially allergic symptoms associated with the second dose that were self-limited, mild, and/or resolved with antihistamines alone.

"These reactions could include symptoms such as itching or hives or flushing. The patients included were all advised by allergy specialists after their dose one reaction," said Matthew S Krantz, MD, of Vanderbilt University Medical Centre.

These immediate onset mRNA vaccine reactions may not be mechanistically caused by classic allergy, called immediate hypersensitivity or Ig-E-mediated hypersensitivity, the researchers explained.

For classic allergy, re-exposure to the allergen causes the same or even worse symptoms, they added.

The findings suggest that it's safe for most individuals to receive a second dose of the mRNA Covid-19 vaccine, said Aleena Banerji, MD, clinical director of the Allergy and Clinical Immunology Unit at MGH.

"After first dose reactions, allergy specialists may be useful to help guide risk/benefit assessments and assist with completion of safe vaccination," she said.