It’s long been established that the single-shot vaccine produced by J&J is nowhere near as effective as two doses of the mRNA vaccine — initially viewed as a tradeoff between accessibility and efficacy.
But as scientists revealed in their final analysis of J&J’s Phase III study, the vaccine may be even less effective in the longer term.
After tracking about 39,000 participants for a median of four months (8,940 of whom had at least six months of follow-up), researchers concluded in a paper published on the New England Journal of Medicine:
A single dose of Ad26.COV2.S provided 52.9% protection against moderate to severe–critical Covid-19. Protection varied according to variant; higher protection was observed against severe Covid-19, medical intervention, and death than against other end points and lasted for 6 months or longer.
Looking at least 28 days after administration, 3 Covid-19–related deaths occurred in the vaccine group (all in participants who were ≥60 years of age), as compared with 17 in the placebo group.
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They noted that the original strain of SARS-CoV-2 and variants like Alpha, Beta and Lambda were responsible for many of the infections and severe cases, whereas Delta and Omicron were not prevalent during the double-blind.
The study was conducted across multiple countries including the US, South Africa, Brazil and Peru.
The relatively low efficacy would come as little surprise. Given their superior profiles, Pfizer/BioNTech and Moderna’s vaccines have emerged as the preferred choice in places that can afford options, and a rare side effect — risks of blood clot — has pushed the CDC to recommend the two mRNA shots over J&J’s jab. The FDA made a similar recommendation about boosters.
Still, the underwhelming data follow a streak of setbacks for J&J, including a chaotic episode with its contract manufacturer, Emergent, as it tried to ramp up production early in the pandemic. And a recent pause in production at a key Dutch plant, as reported by the New York Times, raised new questions.
For those who are allergic to ingredients of the mRNA vaccine, though, it remains the only option — and the same might be true for countries that find it hard to distribute or store other shots. In its NEJM publication, J&J signaled it will continue to focus on delivering its vaccine to the developing world.
Overall, our findings indicate that a single dose of Ad26.COV2.S provided protection against severe disease and hospitalization, which could be important in regions requiring mass vaccination or in populations with poor adherence to two-dose prime regimens, and support the use of Ad26.COV2.S in the ongoing effort against the global Covid-19 pandemic.
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