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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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In general, all medications, including intramuscular, intradermal, and nasal-spray vaccines, have side effects and the potential for allergic reactions. For most medicines and vaccines, the side effects or reactions are infrequent and are minimal if they do occur. The seasonal and pandemic vaccines (including nasal sprays and intradermal vaccine) are no different. What is different about the side effects of flu vaccines is that the occasional side effects seen with all flu vaccines usually resemble the flu disease; about 5%-10% of people experience mild side effects, such as headache, nasal congestion, low-grade fever, sore throat, or muscle cramps, for about a day after vaccination. Although these are short-lived, some people think they contracted the flu from the vaccine. This is a myth. The intramuscular and intradermal vaccines contain no live virus, so the vaccine cannot transmit the disease. Although the nasal-spray vaccines contain live virus, the vast majority of viruses that are attenuated (altered so they will not replicate or do so poorly) will not be able to cause influenza in people with normal immune systems and good health because the attenuated viruses replicate poorly or not at all in these people. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past, but they can occur in some adults. About one-third or fewer of those vaccinated develop soreness and occasional redness at the injection site. Allergic reactions are rare; however, people allergic to eggs should not get the intramuscular or nasal-spray vaccine (both seasonal and H1N1). Intramuscular vaccine shots are usually mildly painful when injected into muscle tissue, the new intradermal shots use a very small needle and require 40% less viral antigen, and most people find them to be far less painful than the intramuscular shots.

The CDC published new safety data on the H1N1 vaccine. They concluded the vaccine showed a good safety profile. For example, after about 50 million doses, 204 serious events were recorded (defined as life-threatening or resulting in death, major disability, and abnormal conditions at birth, hospitalization, or extension of an existing hospitalization). Included in this number are 13 deaths, 10 cases of Guillain-Barré syndrome, and 19 cases of anaphylaxis. The report does not indicate if vaccination with H1N1 vaccine caused these problems, but investigations by the CDC of each case are ongoing to further determine if these events are simply concurrent and not related to the vaccine or if vaccine played any significant role in the serious events. These studies are ongoing since H1N1 strains have become part of the trivalent seasonal vaccine for the last two years. Currently, the CDC concludes that the seasonal trivalent vaccines are safe, but are still monitoring the vaccines for any problems, as with all vaccines.

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