Did RSV vaccine clinical trials end abruptly for safety concerns?

This tweet is an excellent example of a tactic common among anti-vaxxers: they conflate multiple study results with complex data, withholding and distorting information to blur important distinctions and amp up a single scary claim about perceived danger. The tweet in question makes multiple distinct claims. Our first task is to address each claim on its merits.

Before we jump into the details, note that our tweeter lumps all the trials together, implying that all the different trial concerns are focused on “the RSV vaccine,” as if there is only one. In fact, there are many different RSV vaccine candidates from various manufacturers using different formulations that cover different populations.

There are five distinct claims in this tweet; we’ll address each one in turn.

We’ll begin with the claim that GSK shut down all RSV trials in response to a safety concern. This is not true. Currently, GSK has more than two dozen trials that are ongoing, recently completed, recruiting, or about to start. It’s true that a maternal vaccine trial was stopped for a safety signal that has not been disclosed because study investigators are doing additional analysis. The trial halt demonstrates that safety protocols are working as intended. One purpose of clinical trials is to identify safety concerns before a vaccine is considered by the FDA. In this case, it appears the study investigators are following proper safety procedures.

The second claim concerns one person who died in an RSV study of about 600 adults. Although it is true that one person in the study died, the vaccine did not cause their death. The investigators disclose the reason: toxicity from quetiapine and amlodipine. Quetiapine is an antipsychotic used to treat mood disorders. Amlodipine is a beta blocker, commonly prescribed to treat blood pressure. Quetiapine and amlodipine can sometimes interact with serious consequences, especially if someone accidentally takes too much. Neither of these medications is in the vaccine.

Then, our tweeter claims that Pfizer’s RSV vaccine causes Guillain-Barre Syndrome. Although two Pfizer trial participants (out of roughly 20,000) were diagnosed with Guillain-Barre, these cases are very rare. The two trial patients’ Guillain-Barre syndrome symptoms resolved within three to six months,
and Pfizer is conducting a safety study.

The fourth claim suggests that the RSV vaccine was fast-tracked by the FDA despite an early halt of Pfizer’s safety trials. In fact, Pfizer did not stop “safety trials” early. Instead, Pfizer stopped enrollment for the trial — they stopped accepting new patients as the trial continued because they already had the data they needed to show that the vaccine was safe and effective. This is a reasonable resource-saving measure. If you have the data you need to submit a vaccine to the FDA, there’s no reason to enroll additional people. Meanwhile “pre-planned safety reviews” throughout the trial showed “no safety concerns for both the vaccinated individuals and their newborns.” When the FDA reviews the safety data, it will be publicly available on the FDA website. It is true that the FDA fast-tracked Pfizer’s maternal RSV vaccine—back in 2018. It doesn’t appear the FDA is rushing the vaccine to market.

Only the final claim (that GSK and Pfizer vaccines use the “exact same technology”) contains more truth than fiction. Pfizer and GSK vaccines are both mRNA vaccines, so they do use the same technology. But there are still proprietary differences between them, so it is not correct to claim these vaccines are “exactly” the same.