First of all, we need to define some terms. Researchers do not use the phrase, "vaccine injury" -- that's a phrase from the anti-vaccination movement.
Let's say you choose to get yourself an influenza vaccine. Within hours or days of receiving the vaccine, you have an episode of ill-health (bear with me, here). The ill-health can be one of two things:
- An Adverse Event: A new medical or physical adverse state, associated in time with the receipt of the vaccine. This state may or may not have anything to do with the receipt of the vaccine -- it just follows the receipt of the vaccine.
- An Adverse Reaction: A new medical or physical adverse state (or more rarely, the worsening of a previous adverse state) that can be reliably said to be caused by receipt of the vaccine.
In the research literature, the phrase adverse events following immunization (AEFI) is used.
Most physicians and vaccine researchers would say that yes, serious or persistent adverse reactions to vaccines happen, but they are very, very rare. The United States has two formal, funded ways of tracking adverse events: The Vaccine Adverse Events Reporting System, or VAERS, and the Vaccine Safety Datalink (more on VSD in a later post).
VAERS, by its structure, is noisy: that is, there are a lot of reports of adverse events that have nothing to do with vaccines. Loughlin et al., in Causality assessment of adverse events reported to the Vaccine Adverse Event Reporting System (VAERS), found that only 3% of the reports were "classified as definitely causally related to vaccine received."
How else can we estimate the risk posed by a particular vaccine? Well, the US also has the National Vaccine Injury Compensation Program (NVICP), established in 1986, which compensates individuals who may have been injured by vaccines. (A more complete description is available at History of Vaccines.) NVICP, from time to time, publishes statistical reports. Lately, they have taken to publishing a table of compensated injuries, sorted by vaccine, "National Vaccine Injury Compensation Program (VICP) Adjudication Categories by Vaccine for Claims Filed Calendar Year 2006 to Present". I decided to look at the rate of compensable awards per 1,00,000 doses distributed, for each vaccine in the talbe.
First I looked at those for which there was a concession or court decision . I sorted the vaccines from the highest percentage of awards to the lowest (you can click to enlarge.) The single-antigen rubella vaccine (which is no longer available in the US) has the highest rate of award at 2.37 per million doses, followed by the Diphtheria + Tetanus vaccine, at 1.53/million. The rate drops off precipitously thereafter. The first vaccine on the pediatric schedule to be listed is the MMR +Varicella, with 0.73 awards per million doses.
Then I looked at just the settlement  cases. This time, the single-antigen measles vaccine (which is no longer available in the US) had the highest rate of awards, but this may well be a function of small numbers. The first vaccine on the pediatric schedule to be listed is the DTaP, with 0.99 awards per million doses.
Finally, I looked at the total compensated cases. Again, the single-antigen measles vaccine (again no longer available in the US) was at the top. The first vaccine on the current pediatric schedule to be listed is the MMR +Varicella, with 1.45 awards per million doses.
What can we say about these tables? Bad things happen after vaccination -- to a very, very few people. Influenza vaccines are now, by an order of magnitude, the most-often claimed, and compensated, vaccine.
Definitions, from http://www.hrsa.gov/vaccinecompensation/statisticsreport.pdf
[1} Concession: HHS concludes that a petition should be compensated based on a thorough review and analysis of the evidence, including medical records and the scientific and medical literature. The HHS review concludes that the petitioner is entitled to compensation, including a determination either that it is more likely than not that the vaccine caused the injury or the evidence supports fulfillment of the criteria of the Vaccine Injury Table. The Court also determines that the petition should be compensated.
 Court Decision: A special master or the court, within the United States Court of Federal Claims, issues a legal decision after weighing the evidence presented by both sides. HHS abides by the ultimate Court decision even if it maintains its position that the petitioner was not entitled to compensation (e.g., that the injury was not caused by the vaccine).
- For injury claims, compensable court decisions are based in part on one of the following determinations by the court:
- The evidence is legally sufficient to show that the vaccine more likely than not caused (or significantly aggravated) the injury; or
- The injury is listed on, and meets all of the requirements of, the Vaccine Injury Table, and HHS has not proven that a factor unrelated to the vaccine more likely than not caused or significantly aggravated the injury. An injury listed on the Table and meeting all Table requirements is given the legal presumption of causation. It should be noted that conditions are placed on the Table for both scientific and policy reasons.
 Settlement: The petition is resolved via a negotiated settlement between the parties. This settlement is not an admission by the United States or the Secretary of Health and Human Services that the vaccine caused the petitioner’s alleged injuries, and, in settled cases, the Court does not determine that the vaccine caused the injury. A settlement therefore cannot be characterized as a decision by HHS or by the Court that the vaccine caused an injury. Claims may be resolved by settlement for many reasons, including consideration of prior court decisions; a recognition by both parties that there is a risk of loss in proceeding to a decision by the Court making the certainty of settlement more desirable; a desire by both parties to minimize the time and expense associated with litigating a case to conclusion; and a desire by both parties to resolve a case quickly and efficiently.