A handful of companies also are looking at possible new ways to administer immunotherapy, including drops under the tongue, capsules and skin patches, said Fort Lauderdale, Florida, allergist Dr. Linda Cox, former president of the American Academy of Allergy, Asthma and Immunology.
The new tablets are not right for everyone, particularly patients with allergies to multiple substances, Szekely cautioned.
That was the case with one of her patients, 10-year-old Samantha Marshall of Mentor, Ohio, who has been getting allergy shots since last fall.
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"She's not loving them," said her mother, Rachel, who recently asked Szekely about switching to the tablets. Szekely explained that shots are more effective because Rachel is also allergic to weeds and dust mites, and the shots she receives are a customized mix of extracts to all those substances.
The tablets are also pricey: Merck, based in Whitehouse Station, New Jersey, is charging about $8.25 per daily tablet and Stallergenes about $10. Insurers are expected to cover most of the cost, as they usually do with allergy shots. Those generally cost only $15 to $25 per visit without insurance, because they're given by a nurse.
Allergy tablets are less likely to trigger a dangerous allergic reaction than shots, which have been used for a century, Cox said.
In Merck's testing, about 5 percent of patients experienced tingling, itching or swelling in the mouth or tongue, said Dr. Sean Curtis, Merck's head of respiratory and immunology research. Less than 1 percent had serious reactions, nearly all after the first dose.
Longtime hay fever sufferer Kim Steen of Sidman, Pennsylvania, participated in one of Merck's studies last year.
"After the second, maybe third week, I started noticing a difference in the symptoms," said the 41-year-old contracts administrator. "It was pretty significant, not feeling like you have a cold all the time."
Prevalence of hay fever in the U.S. has declined slightly since 2000, according to National Center for Health Statistics data. In 2012, about 17.6 million adults, or 7.5 percent, reported having hay fever, as did about 6.6 million children, or 9 percent. Millions more don't see a doctor and get by with nonprescription medicines like Benadryl or Claritin.
Treatment can be tricky because of body chemistry differences and the complexity of the immune system, which is still poorly understood.
"You can't just have one size fits all," Szekely said.
For people with mild hay fever, inexpensive pills that suppress immune chemicals called histamines work well. Allegra, Benadryl, Claritin and Zyrtec are available without prescription, often competing with store brands.
Other patients fare better on prescription pills or nasal sprays. But for patients with severe allergies, those aren't enough. They suffer—though hardly in silence—or try allergy shots.
Rarely, the shots cause systemic allergic reactions, from hives and itching to dangerous airway narrowing, because small amounts of allergen circulate in the bloodstream. That's why patients must be observed by a nurse for a half-hour after each shot.