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.
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.
Influenza (flu) vaccines are nasal sprays or injections currently composed
either of live flu viruses that have been attenuated (rendered much less able to
cause infection) or killed viruses (unable to replicate) that, when administered
to individuals, generate an immune response that will be strong enough to
protect that individual from developing influenza disease. The design of the
vaccine depends on how it is usually administered; the live attenuated vaccine
is usually administered by a nasal spray, while the killed virus is usually
administered by an intramuscular injection (shot), usually into the deltoid
(arm) muscle; there is a vaccine also available for intradermal injection. People cannot get the flu from the injected vaccine because the vaccine contains no live virus. However, nasal sprays use attenuated viruses (meaning that the viruses are live but cannot effectively cause disease) that, in some people (immunodepressed) may cause mild flu-like symptoms.
Flu vaccines can be quite different based on the viral type(s) used to make
the vaccine. For example, seasonal vaccines usually are made up of a combination
of three different influenza viruses (flu strains that differ in some of
their surface antigens) that experts choose because the strains represent the
most likely viruses to emerge in an upcoming flu season. Pandemic vaccines
differ from seasonal vaccines in several ways. First, the vaccines are usually
made from new flu virus, not detected in previous flu seasons by flu experts and
not included in the seasonal flu vaccines. These flu viruses are usually so new that
they are not easily recognized by most human immune systems and quickly spread
globally. Pandemic flu vaccines contain only a single strain of the
pandemic virus (for example, H1N1 virus) instead of the usual three (trivalent)
flu types used in a seasonal vaccine mixture.
Seasonal vaccines are synthesized and distributed before the start of flu
season (designated as Oct. 4, each year) while pandemic vaccines, unfortunately, have to be
synthesized and distributed only after the pandemic virus has been identified
and started its global spread.
Currently, all commercially available flu vaccines are made from viruses cultivated in chicken eggs and then collected, purified, tested for safety and efficacy, and once approved, distributed to care providers. This process usually takes about six months to accomplish, which gives a pandemic flu virus a long time to circulate and infect populations before a vaccine can be developed. However, future vaccines may be synthesized differently as current techniques are time-consuming, expensive, and yield vaccines that usually protect against only those viral strains present in the vaccine; the protection does not extend to the wide spectrum of flu virus strains. This limited protection is the reason that new flu vaccines are developed each year.