Allergy shots are effective and safe for reducing symptoms of hay fever, according to a new review. The injection series caused no deaths and few serious adverse reactions in 51 controlled studies.

Dr. Moises Calderon, of Royal Brompton Hospital in London, and colleagues evaluated the results from randomized, double-blind, placebo-controlled studies in patients with seasonal allergic rhinitis due to tree, grass or weed pollens. The studies involved 2,871 participants.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Hay fever, or allergic rhinitis, is an immune reaction to allergens such as dust, pollen, pet dander or mold. It usually results in sneezing, watery eyes and an itchy, drippy nose when sufferers come into contact with their allergy triggers.

The incidence of hay fever has been on the rise worldwide over the last two decades, especially in developed countries. Some allergy patients can control their symptoms by avoiding their allergy triggers or by taking antihistamines or other drugs, including nasal steroids. Other patients need stronger measures.

In allergy shot regimens, also known as immunotherapy, tiny amounts of an allergen, such as pollen, are injected under the skin, with the dosages gradually increased over the course of the treatment. Injections can contain one or more allergens.

After the initial treatment, the patient usually undergoes a series of maintenance injections over the next several years. This essentially desensitizes the patient to the allergen.

But deaths or serious adverse reactions to immunotherapy have been reported, causing its use to be limited in some parts of the world.

However, the Cochrane reviewers determined that the injections resulted in significant reductions in symptoms and less need for allergy medications when used in suitably selected patients with hay fever. Overall, quality of life was better for people who had undergone the treatment. The studies showed no long-term consequences from adverse events and no fatalities.

"We conclude that injection immunotherapy is a safe and valid treatment option in patients with seasonal allergic rhinitis," the reviewers said.

The studies covered in the review used treatments ranging in length from three days to three years. Patients were shown to have allergies by a blood test or a skin-prick test.

The use of this treatment is extremely well accepted by allergists, but has been met with some skepticism by the rest of the medical community, said allergist Linda Cox, M.D. "I think it has always been a given that immunotherapy is effective for hay fever. There is very little debate on that," said Cox, who is chair of the Immunotherapy and Allergy Diagnostics Committee of the American Academy of Allergy, Asthma and Immunology.

Immunotherapy is especially safe when done by an allergist, who is trained to deal with the rare instances of adverse reactions to the injections, Cox said. The leading risk factor for an adverse reaction to the shots is symptomatic asthma.

Adverse reactions to injections include itching of the nose and eyes, redness of the face, itching of the throat with cough, moderate wheezing and hives. The review reported two cases of anaphylaxis, a serious allergic reaction, among patients receiving injections.

For the most part, adverse reactions that occurred were generally mild, and those that were not responded to injections of adrenaline, the review noted.

Between 13 percent and 38 percent of people with hay fever also suffer from asthma, making them poor candidates for allergy shot regimens, according to the Cochrane authors.

The reviewers did not analyze cost-effectiveness, as few studies of the costs of the treatment have been performed.

More important is that the treatment has been shown to alter the progression of the allergic response, said Cox, who has a practice in Fort Lauderdale, Fla. Patients who undergo immunotherapy are less likely to go on to develop asthma, she said. "There is a significant difference in the development of asthma."