Second mRNA vaccine shot safe for people who had allergic reactions to first shot: US study

Of the 189 patients who participated in the study, 130 received the Moderna vaccine, while 59 got the Pfizer-BioNTech vaccine. Second dose was administered to 159 subjects.

Representative Image | A vial of Moderna Covid vaccine | ANI

New Delhi: People who experience a moderate allergic reaction from the first shot of Covid mRNA vaccines can safely take the second shot as well, according to researchers in the US, who conducted a small multi-centre trial between 1 January and 31 March this year.

Allergic reactions such as skin redness, dizziness or lightheadedness, tingling, throat tightness, hives and shortness of breath have been reported to be as high as two per cent in the US, with anaphylaxis — a severe, potentially life-threatening allergic reaction — occurring in up to 2.5 per 10,000 individuals who took the vaccine.

Researchers — including those from Massachusetts General Hospital, Brigham and Women’s Hospital and Yale School of Medicine — looked at patients who had had an immediate allergic reaction to the Pfizer-BioNTech or Moderna vaccine.

Both are Messenger RNA or mRNA vaccines, that work by introducing a fragment of a messenger RNA (ribonucleic acid) that codes for and teaches the body to make a protein that is characteristic of the pathogen — using the body’s own translation machinery — and then teaches the immune system to respond to it.

The study was conducted on 189 people who had had an allergic reaction to the vaccine within four hours of receiving the first dose, and were referred for an allergy or immunology consultation.

Of these, 159 patients received a second dose.

Forty-seven of these 159 patients were given antihistamine (anti-allergic) medicines before the second dose was administered. All 159 patients, including 19 people who had experienced anaphylaxis after the first dose, showed tolerance to the second dose, the team wrote in the study.

The study, published in the journal JAMA Internal Medicine Monday, is important because it shows that recipients may safely complete their vaccination process, without having to switch vaccines to avoid allergic reactions suffered after being administered the first dose.

The effect of mixing vaccines has still not been studied extensively.

What study of second dose revealed

Researchers looked at whether patients who had had allergic reactions after the first dose, developed immediate symptoms after the administration of the second dose and whether such symptoms were mild.

Of the 189 patients who participated in this study, 130 (69 per cent) had received the Moderna vaccine, while 59 got the Pfizer-BioNTech vaccine.

The most frequently reported first-dose reactions were flushing or erythema, which occurred in 53 people who received an mRNA vaccine. As many as 49 people reported dizziness or lightheadedness, 46 reported experiencing tingling, 41 experienced throat tightness, 39 got hives on their skin, and 39 reported wheezing or shortness of breath.

Thirty-two patients met the anaphylaxis criteria.

But all 159 patients who received the second dose, including 19 people who had experienced anaphylaxis after the first dose, showed tolerance to the second dose, the team wrote in the study.

While 32 people reported immediate and potentially allergic symptoms after the second dose as well, these were mild and the prior antihistamine medication was enough to treat them.

“Although mild symptoms were reported in 20 per cent of patients with second dose administration, all patients who received a second dose safely completed their vaccination series and could use mRNA Covid-19 vaccines in the future when indicated,” the researchers wrote in their study.

The US Centers for Disease Control and Prevention had recommended that individuals with an immediate and potentially allergic reaction to the first dose of mRNA vaccines can complete their vaccination by taking a single dose of the Janssen Ad26.CoV2.S vaccine developed by Johnson & Johnson. Janssen is an adenovirus vaccine, the technology behind which has been in use for a long time now.

However, the researchers who conducted this study now suggest that most patients with immediate and potentially allergic reactions to mRNA Covid-19 vaccines can tolerate a second dose.

Since the effect of mixing vaccines is still not studied, it may not be necessary to switch vaccines, the researchers concluded.

(Edited by Poulomi Banerjee)