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Advantages of SLIT

SLIT has two well recognized advantages: it is very safe and at the same time it is very efficacious.


The first and perhaps most important feature of SLIT is that it is a very safe treatment modality. Administration of injectable allergy vaccines carries the risk of eliciting a severe reaction even with the occasional risk of death.12,13

In the extensive European literature about SLIT, including large series reviewing more than 20 years of experience, no deaths have ever been reported as a consequence of administration of SLIT for the treatment of inhalant immunotherapy. 11,16

A review of Pub Med was done at the time of writing this information and no reference to mortality after SLIT could be found.


Reported reactions to SLIT administration include -amongst other complaints- itching of the tongue or the lips, nausea, stomach ache, skin rash usually in the lip area or face, more rarely, headaches. There are sporadic reports of severe reactions like urticaria, or asthma, but these reports do not appear in studies involving a large number of patients that include a control group. Because the reactions related to SLIT administration are usually minor, they are known as adverse events (AE’s) in the world’s literature. For more on Adverse Events click here.

There are only a handful of cases published in the world’s literature of a severe reaction occurring after SLIT administration 17-21 and again, to this date there is no single case of mortality after SLIT administration. This was true in 2003 11 and continued to be true in 201122.

Severe reactions after SLIT administration

All the reports on isolated cases of severe reactions after SLIT administration 17-21 were reviewed. In my opinion these cases were not well managed: In one of the cases, the treatment was not interrupted when an adverse event developed rather treatment continued (with the same dose that elicited an initial minor reaction) and eventually an asthma attack ensued. In other cases asthmatic patients (that are the most sensitive patients and the most difficult patients to treat) were treated either with a rush technique (where the dose is progressed extremely quickly) or were treated with a single dose (“one-size-fits-all” kind of treatment) that obviously will not be appropriate for some individual patients.

We strongly feel that the management of the allergic patient especially when the patient is asthmatic, should be done carefully, advancing the dose slowly while attempting to attain a safe and persistent change in the patient’s immunological system so that the patient will stop being reactive to the involved allergens.

In our experience, using the protocol above mentioned 1 no case of severe reaction to the administration of SLIT was ever encountered on any patient, pediatric or adult, with or without asthma.

Asthmatic patients are the most difficult patients to treat and usually this type of patient is not offered immunotherapy for the fear of eliciting a severe reaction from the treatment. In our office asthmatic patients are routinely evaluated and successfully treated. 

Asthma is a condition that carries the risk of mortality. Even to this day several thousand people die from asthma in the US 23,24  We have successfully treated asthmatic patients without ever encountering any problems 25  Not only they get better but when medication use is considered in the response to treatment, and if the medication can be loosely classified as “asthma pumps” and “allergy medications” we consistently find that the asthma pumps are the first group of medications that the patient does not need any more after a few months of immunotherapy treatment.

Still caution is required for the administration of immunotherapy even if the administration route is sublingual rather than shots. For this reason

    1. We always prescribe an Epi-Pen® for patients to have at home in case of an unexpected severe reaction (To the best of our knowledge to this date, none of our patients have needed to use it).
    2. We routinely decrease the dose or even stop the treatment until situation is reassessed as part of the management of a patient on SLIT who presents with any adverse reaction.


The second advantage of SLIT is its efficacy. Safety would be of no practical significance if at the same time it did not make the patient better.

There is an overwhelming amount of evidence mainly in the European literature attesting to SLIT’s efficacy.27-31 Many well done clinical studies demonstrate that SLIT works and works very well. The references here posted are only a minute sample of that body of literature but include some meta-analyses. Meta-analyses are studies done through an in-depth analysis of many already published studies with strict criteria for inclusion in such study. The power of a meta-analysis “to prove a point” is therefore much stronger than the power of a regular study.

There are also studies that suggest that SLIT is as efficacious as SCIT, in other words, that the results obtained by oral vaccines are as good as the results obtained by injectable vaccines (allergy shots). 32-36

In our experience we always observed that patients treated by SLIT fared very well. In our first study1 the majority of the patients that had over time both treatment modalities (drops and shots) reported that both were equally effective but some suggested that drops worked even better than shots. We decided to address this issue scientifically and therefore collected data in 2 large groups of patients, 50 treated with shots versus 47 treated with drops. Results were submitted to a statistician and after statistical analysis it was found that there was no difference in the results of both groups. These results were presented at an Annual Meeting of the American Academy of Otolaryngic Allergy and were later on published in the Journal of Environmental Public Health.37 Our experience then is in agreement with the widespread European literature, which should be no surprise, as the allergic condition is the same all over the world, and the concept of vaccines is similar wherever they are used. (Note that we used the word “similar” rather than “the same” as there are some differences in the way patients are treated according to the training of the allergy-practitioner. This is addressed under the heading “Are all allergy vaccines equal?”)

This is why we feel comfortable stating that while allergic conditions respond to immunotherapy administration either by injectable vaccines (SCIT) or oral vaccines (SLIT) the treatment by SLIT is unquestionably safer. We strongly think that SLIT should be considered the first line of treatment when managing a young patient or an asthmatic patient. While we always stress this point in our publications25,37,38,39 the reality of the US is that SLIT is still a non-FDA approved treatment therefore insurance carriers elect (erroneously in our view) not to reimburse for this treatment modality. There are countless patients with allergic conditions that do not receive specific treatment (immunotherapy). If sublingual immunotherapy was covered by insurance carriers it is likely that many of these patients could get their allergic conditions including asthma under control.


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