Six months ago, the news of a 72% effective vaccine against COVID-19 would have gotten hosannas. Today, however, Johnson & Johnson’s announcement about the clinical success of its one-dose vaccine could get muted by more effective competitors from Pfizer, Moderna, and now Novavax. Plus, their data already shows a larger gap against a new and spreading variant:

Johnson & Johnson announced on Friday that its one-dose coronavirus vaccine provided strong protection against Covid-19, potentially offering the United States a third powerful tool in a desperate race against a worldwide rise in virus mutations.

But the results came with a significant cautionary note: The vaccine’s efficacy rate dropped from 72 percent in the United States to 57 percent in South Africa, where a highly contagious variant is driving most cases. Studies suggest that this variant also blunts the effectiveness of Covid vaccines made by Pfizer-BioNTech, Moderna and Novavax. The variant has spread to at least 31 countries, including the United States, where two cases were documented this week.

Johnson & Johnson said that it planned to apply for emergency authorization of the vaccine from the Food and Drug Administration as soon as next week, putting it on track to receive clearance later in February.

“This is the pandemic vaccine that can make a difference with a single dose,” said Dr. Paul Stoffels, the chief scientific officer of Johnson & Johnson.

Either level of effective response would allow the FDA to issue an emergency-use authorization, as ABC News notes. The question might be whether people would choose to take it, or wait for the two-dose regimen from Pfizer or Moderna with its significantly higher effectiveness:

The Food and Drug Administration (FDA) has said it will consider a vaccine that’s more than 50% effective, and the Johnson & Johnson vaccine exceeds this threshold. An emergency use authorization could be given and people could start receiving shots before the end of February.

With its single-shot administration and more convenient transportation and storage requirements, Mammen calls it a “workhorse vaccine.” …

Although existing FDA-authorized vaccines from Pfizer/BioNTech and Moderna boast roughly 95% efficacy rates against symptomatic disease, and near-perfect protection against severe illness, they also have drawbacks, as they both must be administered in two shots and have more complex storage requirements.

A vaccine with 72% effectiveness would still drive community transmission rates downward significantly, if adopted widely and quickly. The single-shot regimen might make that option more attractive, especially now when supplies are so limited on Pfizer and Moderna and the question of timely access to the second dose still seems potentially troublesome. But there will be some who will refuse the J&J shot in order to aim for the more complete protection from Pfizer or Moderna, and some who will refuse over the ethical issues arising from J&J’s use of embryonic stem cells in production of the vaccine.

Perhaps the issue will get decided on the readiness of the supply. The US already has 100 million doses purchased from J&J as part of Operation Warp Speed, with an option for another 200 million. Unlike Pfizer or Moderna, this vaccine doesn’t require freezing for storage — only refrigeration, which makes distribution much less complicated. If J&J has that ready to ship now or very soon, the lack of logistical complications for this vaccine could allow it to eclipse Pfizer and Moderna and utilize private-sector distribution channels for the fastest and widest vaccination efforts.

The same could be said for Novavax’s two-dose regimen, however. It also only requires refrigerated storage, and its effectiveness is far higher overall and better against the South African variant. J&J’s manufacturing capabilities gives it a presumable edge in production and distribution, but one has to wonder if J&J might be a day late and about 15 points effectiveness short in competing for access to arms in the US.