Lyme Vaccine Shows Efficacy In Human Trials, But Fails Key Statistical Benchmark

A Lyme disease vaccine has shown over 70 percent efficacy in human trials, but high uncertainty means that the studies failed to pass a key statistical benchmark.

The vaccine, developed by Pfizer and the biotech company Valneva, reduced Lyme disease cases by around 73 percent compared to a placebo, a strong result for what would be the only human vaccine for Lyme disease.

“The efficacy was exactly what I expected it to be,” said Tufts University epidemiologist Sam Telford. “It was safe. It will be useful.”

Telford, who has extensive experience studying tick-borne illnesses, has worked on Nantucket for decades and has long been an advocate for a Lyme vaccine.

While the vaccine showed high levels of efficacy, and Pfizer reported no safety concerns, high levels of uncertainty in the results could be an obstacle.

Along with the topline numbers, Pfizer reported a 95 percent confidence interval, a common statistical tool used to account for random variation in results. No two groups of people are identical, and chance will always shape the results of any scientific study, meaning that two identical studies of the same vaccine will likely find at least slightly different results. The 95 percent confidence interval helps to account for this by providing a range of possible results that minimizes the role of randomness.

In this case, the 95 percent confidence interval ranged from around 16 percent efficacy to over 93 percent efficacy, a strikingly wide spread. Often, vaccines need to show 20 percent efficacy to gain approval.

The large spread was due to fewer study participants than expected contracting Lyme disease. Half of the study participants received a placebo, and half received the vaccine. The efficacy of the vaccine was determined by comparing the proportion of participants who contracted Lyme disease in the placebo group with the proportion of participants who contracted Lyme disease after receiving the vaccine. Since fewer participants than expected contracted Lyme disease in both groups, the role of random chance became larger, as one participant coincidentally contracting Lyme disease affects the results more if there are fewer cases overall.

“The results that were posted were not fabulous, but a lot of that is because the last few tick seasons were pretty low,” Telford said, pointing to the drought that gripped much of the world last year and reduced tick numbers.

Telford maintained that this reduction in ticks is true for Nantucket as well, though some conservation professionals who spoke with the Current disagreed. Either way, Nantucket was not ultimately included in Pfizer’s study: the Nantucket location was shut down when Pfizer discontinued half of its participants because of concerns that clinical practice guidelines were violated at certain sites. Ultimately, no misconduct was found, and the shutdown cost Pfizer a large chunk of its sample—perhaps enough to prevent them from clearing the 20 percent statistical threshold.

“That was, to me, unfathomable,” Telford said. “I couldn't believe they did that.”

Still, the efficacy numbers are strong, and Pfizer hopes to gain federal approval for the vaccine.

“Lyme disease can cause potentially serious consequences – where individuals and families face symptoms that can disrupt daily life, work, and long-term health – and there is currently no vaccine available,” said Annaliesa Anderson, Pfizer Senior Vice President and Chief Vaccines Officer, in a statement. “The efficacy shown in the VALOR study of more than 70% is highly encouraging and creates confidence in the vaccine’s potential to protect against this disease that can be debilitating.”

Another obstacle to approval could be Health Secretary Robert F. Kennedy Jr., who has expressed strong skepticism of vaccines and believes a disproven theory that Lyme disease was developed by the United States military as a bioweapon. But Kennedy has also pushed hard for stronger efforts to combat Lyme disease, and Telford expects he will not oppose the vaccine’s approval.

“He makes a lot of noise, but there has been a lot of funding for Lyme disease research coming out of Congress,” Telford said.

Telford said he worried more that the presence of a vaccine could lead to people thinking they didn’t need to take precautions to prevent tick-borne illnesses, even though there would still be a substantial chance of a breakthrough Lyme disease infection for vaccinated individuals, and the vaccine wouldn’t do anything to prevent other tick-borne illnesses, such as babesiosis.