A next-generation yellow fever vaccine called vYF produced immune responses that were noninferior to the standard shot in a phase 2 trial of 568 healthy adults, raising the prospect of a more scalable option for a disease that still drives deadly outbreaks in Africa and South America. By day 29, 328 of 329 participants, or 99.7%, in the vYF group had seroconverted, compared with 155 of 156, or 99.4%, in the YF-VAX group.
The observer-blinded randomized study enrolled adults ages 18 to 60 at 11 centers in the United States and assigned them in a 2:1 ratio to receive a single dose of vYF or YF-VAX. The between-group difference in seroconversion was 0.3 percentage points, with a 95% confidence interval of -1.2 to 3.2, and neutralizing antibody titers peaked at about 1:2654 for vYF and 1:3147 for YF-VAX in participants without prior exposure.
At 1 year, more than 97% of people in both groups remained above the protective threshold of at least 1:10, suggesting the newer vaccine held onto its immune response over time. In a day 11 subgroup, protective titers were seen in 38% of vYF recipients and 61% of YF-VAX recipients, but the study was not powered to judge noninferiority that early.
Read Also: Supreme Court Of The United States birthright fight draws on gun rights logic
Safety findings were broadly similar between the two groups. Solicited adverse events were reported in 56.7% of vYF recipients and 61.1% of YF-VAX recipients, while headache occurred in 36.5% and 37.8%, respectively. No vaccine-related serious adverse events were reported during one year of follow-up.
Read Also: United States Midterm Election: Democrats Trail Republicans in New CNN Poll
The result matters because existing yellow fever vaccines are highly effective, yet outbreaks continue to strain supply chains and leave health systems vulnerable when demand surges. This trial was done in healthy adults in a non-endemic setting, so it does not settle how vYF will perform in children, older adults or immunocompromised people, and the study was not designed to detect rare safety problems. What it does show is that the candidate met its main goal: it matched the standard vaccine on the key immune measure after a single dose.
