People who receive Pfizer's respiratory syncytial virus (RSV) vaccine should be monitored for Guillain-Barré syndrome, according to the authors of a Pfizer-funded study published this week in the New England Journal of Medicine (NEJM).

The paper — one of several published Wednesday reporting interim analyses for Pfizer's phase 3 clinical trials for the RSV vaccine — concluded the vaccine was effective in preventing RSV in adults age 60 and over "without evident safety concerns."

But that same article also flagged Guillain-Barré syndrome as a safety concern moving forward with the vaccine.

"If RSVpreF vaccine [Pfizer's RSV vaccine] is approved and recommended, these adverse events warrant close monitoring in future studies and with real-world data and post-marketing surveillance," the authors of the NEJM study said.

The U.S. Food and Drug Administration (FDA) is expected to approve Pfizer's RSV vaccine for older adults in May.