Flu vaccines in multi-dose vials contain thimerosal to safeguard against contamination of the vial. Most single-dose vials and pre-filled syringes of flu shot and the nasal spray flu vaccine do not contain a preservative because they are intended to be used once.
A list of available flu vaccines and their thimerosal content is available. Preservatives are used to protect vaccines packaged in multi-dose vials.
Each time a vaccine dose is drawn from a multi-dose vial, bacteria or fungi can enter the vial. Receiving a vaccine contaminated with bacteria or fungi can be dangerous. Preservatives are needed to prevent contamination of multi-dose vials each time individual doses are drawn. Phase 1 studies typically enroll less than 20 participants and are designed to look for very common adverse events.
Phase 2 studies may include up to several hundred individuals and are designed to look at the overall safety profile of the vaccine for local reactions such as redness and swelling at the injection site as well as general side effects that may occur with some vaccines such as fever.
For phase 3 studies, the sample size is often determined by the number required to establish efficacy of the new vaccine, which may be in the thousands or tens of thousands of subjects. Phase 3 studies are usually of sufficient size to detect less common adverse events, such as those occurring at rates of 1 in to 1 in For vaccines given concomitantly with other vaccines under the routine immunization schedules, the safety of new vaccines typically is studied with concurrent administration of these other vaccines.
In addition, FDA carefully reviews information on the manufacturing process of new vaccines, and testing is performed on individual lots for safety and potency. If product development is successful, the completion of all three phases of clinical development can be followed by submission of a Biologics License Application BLA. Following FDA's review of a license application for a new indication, the sponsor and FDA usually present their findings to an expert advisory committee in an open public meeting for comment and advice.
The advisory committee provides advice to FDA on approval or disapproval. Vaccine approval also requires the provision of adequate information labeling to health care providers and the public on the vaccine's proper use, including its potential benefits and risks, and its indications and contraindications.
The safety of new vaccines continues to be monitored following licensure in several ways. As a spontaneous reporting system, VAERS has several limitations including under-reporting, incompleteness of reports, lack of consistent diagnostic criteria, and the inability in most cases to establish a cause and effect relationship. VAERS is useful, however, for raising "red-flags" and subsequently generating hypotheses that can be tested further in controlled clinical trials or epidemiological studies.
As part of a post-licensure commitment, FDA often asks the manufacturer to conduct additional clinical studies sometimes called phase 4 studies , to further evaluate safety, and to provide this information to FDA in a timely manner.
In addition, controlled epidemiological studies may be conducted using pre-established large-linked databases, which have improved ability to evaluate whether rare adverse events are caused by vaccination. Preservatives are compounds that kill or prevent the growth of microorganisms, such as bacteria or fungi. They are used in vaccines to prevent bacterial or fungal growth in the event that the vaccine is accidentally contaminated, as might occur with repeated puncture of multi-dose vials.
Vaccines, both in the United States and throughout other parts of the world, are commonly packaged in multi-dose vials. In some cases, preservatives are added during manufacture to prevent microbial growth; with changes in manufacturing technology, however, the need to add preservatives during the manufacturing process has decreased markedly.
Preservatives have been used in vaccines for over 70 years. The requirement for a preservative in multi-dose, multi-entry vials was placed into the Code of Federal Regulations 21 CFR There are exceptions to this requirement for preservative, primarily involving the live-attenuated viral vaccines. The general need for preservatives in multi-dose vials has been underscored by cases in which multi-dose vials that did not contain preservatives become contaminated during use and caused fatal infections in vaccine recipients; cf.
Thimerosal is a preservative that has been used in some vaccines since the 's, when it was first introduced by Eli Lilly Company. It is At concentrations found in vaccines, it meets the requirements for a preservative as set forth by the United States Pharmacopeia ; that is, it kills the specified challenge organisms and is able to prevent the growth of the challenge fungi. Prior to its introduction in the 's, data were available in several animal species and humans providing evidence for its safety and effectiveness as a preservative.
Since then, thimerosal has a long record of safe and effective use preventing bacterial and fungal contamination of vaccines, with no ill effects established other than minor local reactions at the site of injection.
As a vaccine preservative, thimerosal is used in concentrations of 0. A vaccine containing 0. The use of mercury-containing preservatives in vaccines has declined markedly since FDA is continuing its efforts toward reducing or removing thimerosal from all existing vaccines.
Much progress has been made to date. FDA has been actively working with manufacturers, particularly those that manufacture childhood vaccines, to reach the goal of eliminating thimerosal from vaccines, and has been collaborating with other PHS agencies to further evaluate the potential health effects of thimerosal.
In this regard, all vaccines routinely recommended for children 6 years of age or younger and marketed in the U. What has FDA done to address the issue of mercury containing preservatives in vaccines? Conducted in , this review found no evidence of harm from the use of thimerosal as a vaccine preservative, other than local hypersensitivity reactions. However, depending on the vaccine formulations used and the weight of the infant, some infants could have been exposed to cumulative levels of mercury during the first six months of life that exceeded EPA recommended guidelines for safe intake of methylmercury.
The U. Public Health Service agencies have collaborated with various investigators to initiate further studies to better understand any possible health effects from exposure to thimerosal in vaccines. Data reviewed did not demonstrate convincing evidence of toxicity from doses of thimerosal used in vaccines. In case reports of accidental high-dose exposures in humans to thimerosal or ethyl mercury toxicity was demonstrated only at exposures that were or times that found in vaccines.
In its report of October 1, , the IOM's Immunization Safety Review Committee concluded that the evidence is inadequate to either accept or reject a causal relationship between thimerosal exposure from childhood vaccines and the neurodevelopmental disorders of autism, attention deficit hyperactivity disorder ADHD , and speech or language delay.
At that time the committee's conclusion was based on the fact that there were no published epidemiological studies examining the potential association between thimerosal-containing vaccines and neurodevelopmental disorders.
The Committee did conclude that the hypothesis that exposure to thimerosal-containing vaccines could be associated with neurodevelopmental disorders was biologically plausible. However, additional studies were needed to establish or reject a causal relationship. The Committee stated that the effort to remove thimerosal from vaccines was "a prudent measure in support of the public health goal to reduce mercury exposure of infants and children as much as possible.
In , the IOM's Immunization Safety Review Committee again examined the hypothesis that vaccines, specifically the MMR vaccines and thimerosal containing vaccines, are causally associated with autism. In this report, the committee incorporated new epidemiological evidence from the U. The committee concluded that this body of evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism, and that hypotheses generated to date concerning a biological mechanism for such causality are theoretical only.
Further, the committee stated that the benefits of vaccination are proven and the hypothesis of susceptible populations is presently speculative, and that widespread rejection of vaccines would lead to increases in incidences of serious infectious diseases like measles, whooping cough and Hib bacterial meningitis.
Since , all vaccines recommended for children 6 years of age and younger have contained either no thimerosal or only trace amounts, with the exception of inactivated influenza vaccines, which are marketed in both the preservative-free and thimerosal-preservative-containing formulations. Thimerosal-preservative free influenza vaccine licensed for use in children six to 59 months of age is available in limited supply.
Nevertheless, FDA is in discussions with manufacturers of influenza vaccine regarding their capacity to increase the supply of vaccine without thimerosal as a preservative. Additionally, new pediatric vaccines that have received licensure do not contain thimerosal. Oberg, MD, a pediatrician at Hennepin County Medical Center in Minneapolis and a pediatrics professor at the University of Minnesota, said most studies have not shown any clear link between thimerosal and neurodevelopmental problems.
But he said he would prefer to use a thimerosal-free flu vaccine for young children if it's available. If a parent was reluctant to use the vaccine because of thimerosal, I'd defer to their wishes. He added that, given the limited supply of thimerosal-free vaccine, "I might be a little more proactive about making sure that option is available to my patients and their parents as soon as possible.
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