One of the most important considerations of the safety and effectiveness of a vaccine is determining whether an adverse reaction is related to the vaccine. Obviously, this isn’t as easy as the anti-vaccine activists pretend it is.

Millions of people receive vaccines every year, and by chance, some will experience health events within a few days or weeks after vaccination. Scientists need to determine whether the vaccine caused it or whether it was just a random coincidence.

There are logical and scientific processes that determine whether any adverse reaction is related to a vaccine. These steps basically follow the Bradford Hill criteria, which provide a set of objective criteria that could provide epidemiological evidence of causality between a cause and effect. This article will review this process for vaccines.

Step 1 — compare expected and observed adverse reaction

Scientists calculate the expected number of adverse events in a group over a given time period, regardless of vaccination status. For example, if you were to try to show that autism is an adverse event for a vaccine, you would first determine what the background rate of autism is in a large group.

Then, researchers determine how many adverse events occur after vaccination. They compare this data to the background rate, and if it is statistically significantly higher in the vaccinated group, researchers would have preliminary evidence.

So, using our example of autism, if the expected rate was 50 in a particular group but 100 were observed, that would be some evidence of a correlation between vaccination and autism. However, we must remember that correlation does not imply causation — we need more evidence to show a link between the adverse events.

This data must be strong (statistically significant) and specific.

Step 2 — determine if there is a pattern

Researchers need to determine whether the same adverse events are observed in different demographic groups and in different, unrelated studies. The data must be consistent between different studies — if one study shows a link between adverse events and a vaccine, but ten others don’t, the data is not only inconsistent; it probably shows there is no link.

In addition, the researchers will examine the temporal relationships — does the adverse event occur in a specific time window? This is important because the biological effect of vaccines is usually short-term, so if there’s a pattern to the timing, it could indicate a link.

Step 3 — biological plausibility

This is the most important step, because it is necessary to determine whether a correlation has a biological explanation.

When someone says that vaccines cause autism, is it even biologically plausible? Is there some biological mechanism between the vaccine, its ingredients, or the vaccination itself that can be plausibly linked to an adverse event, like autism? After nearly three decades of being involved with vaccine research, I have yet to read a legitimate explanation of a potential biologically plausible link between any vaccine and autism.

One cannot state that there is a biologically plausible relationship — it must be based on the science of vaccines. This requires an understanding of that science, including immunology, physiology, and other fields that may provide a scientifically valid link between the vaccine and adverse events.

Summary

This logical stepwise process provides scientists with the data that can determine if a rare adverse event is linked to a vaccine. Or not.

It is a rigorous, worldwide process that combines the fields of epidemiology, statistics, medicine, and biology. It is not one person drawing a conclusion from data from one study.

So that’s why using data in VAERS is not a replacement for large, high-quality case-control studies that rarely show a statistically significant correlation between vaccines and some claimed adverse events.

By the way, science has affirmative evidence that there is no link between vaccines and autism. Anti-vaccine claims about autism provide no evidence of a correlation between vaccines and autism, let alone causation.

Help the Skeptical Raptor keep writing about vaccines

There are four ways you can help contribute to keeping this website running at full speed:

1. GoFundMe.
2. Subscribing via Patreon.
3. Buying your favorite stuff on Amazon.
4. Sharing this article on Social Media.