Study Shows Pfizer’s Updated mRNA COVID-19 Vaccine Elicits Strong Immune Response

Pfizer and BioNTech updated mRNA COVID-19 vaccine for the 2025-2026 season produced strong immune responses, boosting neutralizing antibody levels by at least fourfold in older people and those with underlying medical conditions. This year’s Pfizer-BioNTech vaccine targets the SARS-CoV-2 strain LP.8.1, a variant in the JN.1 family.

The Phase III trial included 100 people, 50 of whom were age 65 or older and 50 people age 18 to 64 with an underlying condition. Those conditions included asthma, diabetes, heart conditions, HIV, mental health conditions, Parkinson’s disease, obesity or smoking. All participants had gotten last season’s COVID shot at least six months prior to the trial and had not gotten any other COVID-19 vaccines or a COVID-19 infection since then. In both age groups in the trial, the LP.8.1 vaccines boosted LP.8.1-neutralizing antibody levels by at least fourfold, on average. There were no new safety concerns relative to previous versions of the shot.

While LP.8.1 was the leading variant at the time, regulators had to make a call on the target strain for this year’s vaccine, the current leading strain is XFG, another JN.1 family member. Pfizer did testing in mice previously to show that an LP.8.1-targeting vaccine would remain effective against XFG (and other emerging variants) and beat out last year’s vaccine at providing protection.