Ad26COV2S

Ad26.COV2.S, also known as the Janssen COVID-19 vaccine, is a viral vector vaccine developed by Janssen Biotech, a subsidiary of Johnson & Johnson. It uses a replication-incompetent adenovirus serotype 26 (Ad26) vector to deliver DNA encoding the SARS-CoV-2 spike protein, prompting an immune response. The vaccine is administered by intramuscular injection and was initially studied as a single-dose regimen, with later research evaluating booster dosing to enhance and prolong protection.

In clinical trials, Ad26.COV2.S showed protection against symptomatic COVID-19 after a single dose, with higher protection against severe disease and hospitalization. Efficacy varied by region and across viral variants, and real-world data indicated the vaccine could reduce hospitalizations and severe outcomes in various settings. Booster-dose studies and evolving guidance have influenced recommendations on additional doses and scheduling.

Safety data identified common short-term adverse events such as injection-site pain, fatigue, headache, muscle aches, fever, and chills. Rare but notable adverse events include thrombosis with thrombocytopenia syndrome (TTS) and, more rarely, Guillain-Barré syndrome; regulatory agencies have closely monitored these signals and updated labeling and guidance accordingly. As with all vaccines, risk-benefit judgments consider the rarity of these events relative to protection against severe disease.

Regulatory status and use vary by country. In the United States, the vaccine received Emergency Use Authorization from the FDA in 2021 for adults, with use expanding or contracting over time as safety monitoring and supply evolved. In some regions, uptake declined as other vaccines became more widely available, though Ad26.COV2.S has continued to be used in certain populations or settings where appropriate.

Storage and handling typically allow refrigeration (2–8°C), facilitating distribution in areas with limited cold-chain infrastructure. The vaccine is packaged for intramuscular administration and is designed for use within standard vaccination programs.