Summary of the prediction
On 31 July 2020, Friedberg asserted that effective COVID-19 vaccines would indeed exist as real, deployable products, and that the remaining uncertainty was about how many doses could be produced and when they would be available.

What actually happened

• In December 2020, the Pfizer–BioNTech COVID‑19 vaccine became the first to receive emergency authorization and be deployed to the public (UK emergency authorization on 2 Dec 2020; US FDA Emergency Use Authorization on 11 Dec 2020).(en.wikipedia.org)
• The Moderna mRNA‑1273 vaccine received US FDA Emergency Use Authorization on 18 Dec 2020, and began deployment shortly thereafter.(en.wikipedia.org)
• By late 2020 and through 2021, multiple vaccines (mRNA and others) were being manufactured and administered globally at scale, not just in clinical trials.
• As of August 2024, about 13.5–13.7 billion COVID‑19 vaccine doses had been administered worldwide, with over 70% of the global population receiving at least one dose, demonstrating massive real‑world deployment and large‑scale manufacturing.(en.wikipedia.org)

Assessment

• Friedberg’s key claim was existence and deployability of effective vaccines ("we're going to have a vaccine"), not just ongoing trials. Multiple such vaccines were indeed developed, authorized, and widely deployed within months of his statement.(en.wikipedia.org)
• The issues that followed were in fact manufacturing volume, distribution, and timing of rollouts across countries, exactly the dimensions he highlighted as the remaining uncertainties.(en.wikipedia.org)

Because effective, widely deployed COVID‑19 vaccines did materialize and the main challenges proved to be production and timing, Friedberg’s prediction is substantively correct.