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For people with peanut allergies, undergoing immunotherapy may actually increase their risk of having allergic or anaphylactic reactions.

Immunotherapy is an experimental treatment for allergies that involves repeated exposure to the allergen in gradually increasing doses, aiming to desensitise the patient鈥檚 immune system.

To get a better understanding of how safe and effective it is, Derek Chu of McMaster University, Canada, and colleagues compiled data from 12 trials involving 1041 patients in total, most of them children aged five to 12. Some of the trials compared immunotherapy with a placebo, while in others, the comparison group were simply told to avoid peanut exposure.

Patients who received immunotherapy had a 22 per cent risk of anaphylaxis 鈥� a life-threatening allergic reaction 鈥� during the follow-up period, which lasted around a year in most studies. That鈥檚 around three times higher than the risk for patients who did not have the therapy.

Despite this, many trials have reported that immunotherapy is successful because participants passed a test in the clinic in which they eat some peanut without having a reaction.

Unpredictable reactions

Chu says these tests are not the most important outcome measure for patients. Even if patients don鈥檛 show a reaction in the clinic, they may not be fully protected, and can go on to have severe reactions.

鈥淐ommon situations patients face can break their protection, often in an unpredictable manner,鈥� says Chu. 鈥淢aybe they鈥檙e sick that day or tired or have an empty stomach; even having a hot shower 鈥� that can break their protection.鈥�

Immunotherapy usually involves daily doses of allergen, often taken by the patient at home. If doses are missed, this can also result in a loss of protection and an allergic reaction to the next dose.

In all the trials, patients were told to avoid exposure to peanuts except for the therapeutic doses, so it鈥檚 likely that the therapy itself caused the increase in reactions.

Food allergies affect up to 8 per cent of children in Europe and North America, and the incidence is rising. Unlike milk and egg allergies, peanut allergy is lifelong in around 80 per cent of cases.

Chu says these results provide patients with the best summary of immunotherapy鈥檚 benefits and risks based on current evidence, and more carefully designed trials are needed to improve outcomes for patients.

鈥淲e need new, safer approaches to this treatment, whether it鈥檚 using immunotherapy or completely different approaches,鈥� he says.