One pervasive myth about vaccines is the belief that vaccines are not proven to be safe, or are not sufficiently tested before arriving in your doctor’s office. This claim couldn’t be further from the truth. Vaccines are rigorously tested and monitored to ensure their safety and effectiveness.
But being the vaccinerds we are, we wouldn't make such a bold claim without supplying evidence to back it up. So here it goes …
In 1998, the first vaccine to prevent rotavirus, RotaShield, emerged onto the market in the U.S. It was a big deal. Public health nerds rejoiced; medical professionals breathed a sigh of relief. Rotavirus, after all, is responsible for an estimated 500,000 deaths from diarrhea worldwide — mostly in small children. The vaccine was yet another major victory in the fight against child mortality.
Less than a year later, however, the vaccine was discontinued.
What happened? Why would a much-awaited vaccine — something we desperately needed — be removed from the shelves?
It’s a good story actually. And one that demonstrates the intense process by which we monitor vaccine safety in the United States.
Before a vaccine is ever approved for use in the U.S., a substantial amount of research has to be done. It’s starts with an exploratory stage, where researches look at pathogens (disease-causing agents) or pieces of pathogens in the laboratory. When they think they have a good candidate, they move on to tissue- or cell-culture systems and animal testing. These stages combined can take an average of 3 to 6 years to complete.
If vaccine candidates are successful after this stage (few are), an application for an Investigational New Drug (IND) is submitted to the Food and Drug Administration. If approved, researchers can start the meat and potatoes of pre-licensure testing: Clinical trials with human subjects.
The trials start out small (20- 80 people) and grow to include tens of thousands of people as the vaccine candidate advances through three phases of testing. If the vaccine candidate is meant for kids, researchers start with adults and then gradually lower the age of participants until they get to the target age. Researchers are also fine-tuning the number of doses, schedule and how the vaccine should be delivered.
The three phases of clinical trials serve to answer two important questions: Is the vaccine candidate safe? And is it effective?
If the answer to both is yes, another request is made to the FDA for the vaccine to be licensed for use in the United States. Once licensed, yet another panel, the Advisory Committee on Immunization Practices (ACIP), reviews all the research, and in some cases investigates serious side effects, in order to decide whether the vaccine should be recommended for general use.
In the case of RotaShield, that whole process — which involved more than 10,000 infants participating in 27 clinical trials done in 9 different countries — took more than 15 years and cost hundreds of millions of dollars.
But safety testing for RotaShield didn’t stop there.
After a vaccine is released into the market, there are a few ways its safety continues to be monitored. The first is a self-reporting system known as the Vaccine Adverse Events Reporting System (VAERS). As we’ve mentioned in previous posts, anyone can report anything to VAERS — even if they aren’t sure the vaccine caused the particular event or condition. The open system has its drawbacks (both underreporting and overreporting can be a problem), but it helps researchers identify rare side effects that didn’t show up during pre-licensure clinical trials.
… Which is what happened with RotaShield.
Ten months after the vaccine was on the market, reports started trickling in of a rare, but serious, event known as intussusception (a cause of intestinal blockage) occurring in small infants who received the vaccine.
A mere 15 VAERS reports out of about a million doses raised alarm. The Centers for Disease Control and Prevention (CDC) temporarily suspended the use of the vaccine and launched an investigation using a system known as the Vaccine Safety Datalink. Within months, the CDC concluded that the risk of intussusception from using RotaSheild was 1 in 10,000. Even with the potentially life-saving attributes of the vaccine, that extremely low level of side effects was too high. The benefits no longer outweighed the risks. The ACIP recommendation was withdrawn, and the vaccine was pulled from the market by the manufacturer. It was the first time in nearly 50 years a vaccine was discontinued because of concerns regarding safety.
An improved, safer Rotavirus vaccine was released seven years later, and yet another became available two years after that. Both are still in regular use today.
Drug regulators are exceptionally cautious with vaccines because they are one of the few medical interventions given to people before they get sick. The bar for safety must be very high. Testing is more extensive with vaccines than other pharmaceutical products — and, surprisingly, much more rigorous than the testing of other products given to healthy people like multi-vitamins or supplements.
Fortunately, examples of “unsafe” vaccines are few and far between. The vaccine monitoring and reporting system is extremely effective and was proven to work when RotaShield was pulled off the market. You can be sure that any vaccine in regular use today ran the gauntlet of clinical trials and safety testing and continues to be rigorously monitored.
Jane manages the Vaccine Finder project at Health Map, the host site of the Disease Daily. Robyn is a contributing writer for the Disease Daily and works as a project manager for a non-profit focused on vaccine education. Both are fully up-to-date on their immunizations.