The prediction was that mRNA COVID‑19 vaccine effectiveness against infection would decline to roughly two‑thirds (about 60–70%) around six months after the initial 2‑dose series.

Real‑world data show substantially lower effectiveness against infection by about 5–6 months, especially once Delta became dominant:

• A large Kaiser Permanente / Pfizer cohort study of BNT162b2 found effectiveness against any SARS‑CoV‑2 infection fell from 88% in the first month after full vaccination to 47% at six months overall, with Delta-specific effectiveness around 53% by four months and non‑Delta effectiveness about 67% at 4–5 months – already below or barely at the lower edge of the predicted 60–70% band and still declining. (pubmed.ncbi.nlm.nih.gov)
• A nationwide Qatar study found BNT162b2 effectiveness against infection peaked early then dropped rapidly, reaching roughly 20% in months 5–7 after the second dose, far below two‑thirds. (pubmed.ncbi.nlm.nih.gov)
• In England’s OpenSAFELY cohort, by weeks 23–26 (about six months) after the second dose, rates of positive SARS‑CoV‑2 tests in vaccinated people were similar to or higher than in unvaccinated people, implying vaccine effectiveness against infection near zero or even negative at that time. (pubmed.ncbi.nlm.nih.gov)

Earlier phase 3 trial follow‑up for BNT162b2 reported high efficacy (around 84–91%) against symptomatic COVID‑19 through six months, but those data were mostly pre‑Delta and not focused specifically on the six‑month point in a real‑world, variant‑mixed setting. (pubmed.ncbi.nlm.nih.gov) Subsequent observational studies across multiple countries consistently show that by roughly six months post‑series, protection against infection had typically fallen below 60%, often much lower, although protection against severe disease remained high.

Because the actual effectiveness against infection at about six months was generally well under the predicted 60–70% (two‑thirds) level, the prediction overestimated how much protection would remain and is best classified as wrong.