WASHINGTON (BLOOMBERG) - Johnson & Johnson's one-shot Covid-19 vaccine may not immediately ease the widespread supply constraints slowing the US immunisation campaign. Yet it appears poised to aid difficult-to-reach populations that need protection from the virus.

That's the message from federal officials who are grappling with how best to distribute Johnson & Johnson's shot once it gets regulatory clearance expected in coming weeks. The Johnson & Johnson vaccine, which can be stored in a refrigerator, offers a logistical advantage over the Pfizer and Moderna two-shot vaccines currently in use that must be kept frozen. Still, it could take some time to shift the pace of the campaign, a top official said Monday (Feb 1).

Johnson & Johnson has clinched a deal to supply the US with 100 million doses of the single-shot vaccine by the end of June. Andy Slavitt, the Biden administration's deputy coordinator for pandemic response, said he wouldn't be "overly confident that those doses would come evenly." Instead, Slavitt said he expects the bulk of supply to be available toward the end of that period.

In a late-stage study of more than 43,000 people, Johnson & Johnson's vaccine prevented 66 per cent of moderate to severe cases of Covid-19, the company announced on Friday, demonstrating lower levels of efficacy than those developed by Pfizer and Moderna. But Johnson & Johnson's shot was particularly effective at stopping severe disease, preventing 85 per cent of severe infections and 100 per cent of hospitalisations and deaths.

Faced with the three vaccines' safety and efficacy profiles, dosing regimens and other requirements, US officials will determine a distribution pattern for them. Deliberating over the optimal use of each vaccine before adding another to the mix will be crucial, said Matthew Hepburn, the US government's Covid-19 response lead.

Johnson & Johnson's vaccine is poised to provide faster protection than its counterparts to people in communities where the virus is spreading quickly, given that immunity ramps up immediately after a single shot, Hepburn said. That also bodes well for places that appear vulnerable to new virus variants, he said.

The logistical ease of Johnson & Johnson's vaccine serves as a crucial public-health tool, Hepburn said. "Frankly, simple is beautiful." Best Shot Anthony Fauci, the top US infectious-disease official, said Friday that federal authorities will talk with governors, mayors and others involved in planning the immunisation campaign to determine which vaccine should go where.

For instance, in rural communities where authorities have been challenged by the freezer requirements, Johnson & Johnson's single dose may be better suited, Fauci said. If communities are seeing fewer people return for a second dose, a one-shot vaccine could alleviate that issue, he added.

"There will be somewhat of a choice at the local level, depending on your needs," Fauci said. "That's a very nice problem to have." Public-health experts want federal authorities to provide clear-cut recommendations to states on which communities will benefit more from the Johnson & Johnson shot compared with the other vaccines.

"States and localities should be given flexibility, but local decisions are better when they're made in light of uniform national guidelines," said David Fleming, the chief medical and public-health officer of Path, a nonprofit global health organisation.

Fleming, a public-health expert and epidemiologist who has held roles at the Centres for Disease Control and Prevention and the Bill & Melinda Gates Foundation, agreed that Johnson & Johnson's vaccine will be particularly useful in rural communities. He also suggested it would be a good choice for people who are unable to travel to health-care facilities and pharmacies.

Submission process

Johnson & Johnson received results from its large, late-stage clinical trial early last week. While the company has yet to provide details to show how the vaccine performed in sub-populations, it said protection was consistent across ages, races, and regions.

Now Johnson & Johnson is preparing documents for regulators in the US and elsewhere to seek an emergency-use authorisation. Chief Scientific Officer Paul Stoffels said in an interview that he expects Johnson & Johnson to approach the US Food and Drug Administration by the end of the week, and obtain a clearance in March.

Once the FDA receives Johnson & Johnson's submission, it must convene a panel of outside experts to review the data and make an independent recommendation. The CDC will organise its own meeting of outside experts, known as the Advisory Committee on Immunisation Practices, or ACIP, to provide guidance on how to best allocate the vaccine and prioritise certain populations.

Together, these processes can take weeks. Pfizer and its partner BioNTech, for example, submitted an application for its vaccine regimen on Nov 20 and three weeks later was authorised for emergency use. Days later, the vaccine was first distributed.

Supply boost

To date, the US has administered 31.8 million doses of the Pfizer-BioNTech and Moderna vaccines, according to Bloomberg's Vaccine Tracker, with an average of 1.35 million doses a day administered last week. Slavitt said there likely won't be an "immediate dramatic shift" when Johnson & Johnson's vaccine gets a green-light from regulators.

Rather, the US will see supply ramp up toward the end of summer, he said. The government has clinched deals with Pfizer and Moderna for a total of 400 million doses by the end of the second quarter. With Johnson & Johnson's added supply, there should be enough shots to inoculate 300 million people by the end of June.

The former leader of Operation Warp Speed, the Trump administration-led effort to develop and distribute vaccines, said he expects Johnson & Johnson's vaccine to have broader reach than the other two vaccines have so far.

"The fact that people will be vaccinated with just one shot, that is transformational," Moncef Slaoui, former chief scientific adviser to Warp Speed, said in an interview.