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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 1933, researchers discovered that viruses (influenza virus types A, B, and rarely C) cause influenza (flu). Prior to 1933, a bacterium named Haemophilus was thought to cause the flu. In 1938, Jonas Salk and Thomas Francis developed the first vaccine against flu viruses. This first flu vaccine was used to protect the U.S. military forces against the flu during World War II. Dr. Salk used his experience with influenza vaccine to develop an effective polio vaccine in 1952. Vaccines produced from the 1940s to the 1960s were not as purified as more modern vaccines, and the impurities in vaccines were thought to contribute to side effects such as fever, aches, and fatigue. Since these symptoms were similar to those that accompanied the flu (flu symptoms usually were more severe and lasted longer), people mistakenly thought they got the flu from the vaccination. However, they did not get the flu from the vaccines since the vaccines used killed virus.

In a public vaccination program designed to prevent a pandemic swine flu outbreak in 1979, about 25% of people in the United States were vaccinated. Unfortunately, the 1979 vaccine was associated with a small increased risk of Guillain-Barré syndrome, a serious neurological condition, with the risk estimated to be one to nine excess cases per million doses of vaccine, but no cause for this increase in risk was ever discovered. Fortunately, no pandemic developed, and the vaccination program for that flu virus was cancelled. Since that time, vaccine purification has been improved, and millions of people have continued to be vaccinated every year. Currently, influenza viruses are inoculated into eggs, where they multiply; afterward, they are harvested and separated from most egg particles and egg antigens. Attenuated viruses (for nasal spray) are grown similarly, but strains are selected that only replicate under cool or cold temperatures so they can survive in the cool nasal passages long enough to stimulate an immune response but do not easily replicate and spread to warmer body regions like the lungs.

Because of the potential for widespread infection and deaths that the H1N1 pandemic virus strain seemed to possess, the H1N1 tests were accelerated so that vaccine could be provided before the usual six-month timeline. However, all of the steps (cultivation, safety, efficacy, approval, and distribution) were done in the same way as for seasonal vaccines but over a shorter time period with fewer people involved in the initial trials. Tested and approved H1N1 vaccine started to become available in late September of 2009 (in Europe) and in October 2009 in the Americas and Asia. However, suppliers could not produce enough vaccine because of a low yield of virus from eggs, so there were worldwide shortages. Because of these shortages, the WHO, the CDC, and other organizations recommended first vaccinating the people known to be at high risk for complications or death (described below) if they became infected with H1N1. Changes in vaccine synthesis, testing, and distribution are being considered by the CDC to improve the vaccine response to pandemic flu in the future due to these problems.

Must Read Articles Related to Flu Vaccine

Fever in Adults A fever is a body temperature of 100.4 F or greater. A fever may be caused by a virus, bacteria, fungus, blood clot, tumor, drug, or the environment. Treatment ...learn more >>

Fever in Children Fever is defined as a rectal temperature over 100.4 F or 38.0 C. Fever isn't life-threatening unless it is persistently high -- greater than 107 F rectal temper...learn more >>

Flu in Adults Flu (influenza) is an acute infection of the nose and throat airways. This infection may spread to the lungs. Flu is the most frequent cause of acute respirator...learn more >>

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