Covid-19 coronavirus: One-dose Johnson & Johnson shot offers good protection, new hope against virus

A clinician preparing to administer the Janssen Covid-19 vaccine which only requires on dosage. Photo / via AP

Johnson & Johnson's long-awaited vaccine appears to protect against Covid-19 with just one shot – not as strong as some two-shot rivals but still potentially helpful for a world in dire need of more doses.

J&J said Friday that in the US and seven other countries, the single-shot vaccine was 66 per cent effective overall at preventing moderate to severe illness, and much more protective — 85 per cent — against the most serious symptoms.

There was some geographic variation. The vaccine worked better in the US — 72 per cent effective against moderate to severe Covid-19 – compared to 57 per cent in South Africa, where it was up against an easier-to-spread mutated virus.

Johnson & Johnson's long-awaited Covid-19 vaccine appears to protect against symptomatic illness with just one shot. Photo / AP

"Gambling on one dose was certainly worthwhile," Dr. Mathai Mammen, global research chief for J&J's Janssen Pharmaceutical unit, told the Associated Press.

With vaccinations off to a rocky start globally, experts had been counting on a one-dose vaccine that would stretch scarce supplies and avoid the logistics nightmare of getting people to return for boosters.

But with some other competing vaccines shown to be 95 per cent effective after two doses, at question is whether somewhat less protection is an acceptable tradeoff to get more shots in arms quickly.

"Frankly, simple is beautiful," said Dr Matt Hepburn of Operation Warp Speed, the US government's vaccine initiative.

The company said within a week, it will file an application for emergency use in the US, and then abroad. It expects to supply 100 million doses to the US by June — and a billion doses globally by the end of the year. J&J wouldn't say exactly how much could be ready to ship as soon as US authorities give the green light.

These are preliminary findings from a study of 44,000 volunteers that isn't completed yet. Researchers tracked illnesses starting 28 days after vaccination – about the time when, if participants were getting a two-dose variety instead, they would have needed another shot.

After day 28, no one who got vaccinated needed hospitalisation or died regardless of whether they were exposed to "regular Covid or these particularly nasty variants," Mammen said. When the vaccinated did become infected, they had a milder illness.

Defeating the scourge that has killed more than two million people worldwide will require vaccinating billions, and the shots being rolled out in different countries so far all require two doses a few weeks apart for full protection. Early data is mixed on exactly how well all the different kinds work, but shots made by Pfizer and Moderna appear to be about 95 per cent protective after the second dose.

That makes for a dilemma: Wouldn't people given a choice want a vaccine found to offer much more protection?

Despite news of the one dose Covid vaccines, Johnson & Johnson's stock price dipped. Photo / AP

J&J's Mammen said direct comparisons are difficult because the Pfizer and Moderna vaccines weren't tested when the pandemic was so severe, with record levels of hospitalisations and deaths plus mutant versions of the virus sweeping some countries.

Dr Anthony Fauci, the top US infectious disease official, called that a messaging challenge — because the priority is to protect people from hospitalsation and death, which J&J's vaccine appears to do. Especially in places where it's hard to get people to return for their second dose, the one-dose version could play a key role.

Maybe more important is "a wake-up call" from the study that mutating viruses can challenge vaccines. And the best way to prevent more mutations is "by vaccinating as many people as you possibly can," Fauci said.

All Covid-19 vaccines train the body to recognise the new coronavirus, usually by spotting the spikey protein that coats it. But they're made in very different ways.

J&J's shot uses a cold virus like a Trojan horse to carry the spike gene into the body, where cells make harmless copies of the protein to prime the immune system in case the real virus comes along. It's the same technology the company used in making a successful Ebola vaccine.

Rival AstraZeneca makes a similar cold virus vaccine that requires two doses. Both the AstraZeneca and J&J vaccines can be stored in a refrigerator, making them easier to ship and to use in developing countries than the frozen kind made by Pfizer and Moderna.

It's not clear exactly how well the AstraZeneca version, being used in Britain and several other countries, works. Tests in Britain, South Africa and Brazil suggested two doses are about 70 per cent effective although there are questions about how much protection older adults get. An ongoing US study may provide more information.

J&J said its vaccine works consistently in a broad range of people: A third of participants were over age 60, and more than 40 per ce had other illnesses putting them at risk of severe Covid-19, including obesity, diabetes and HIV.

J&J said the vaccine is safe, with reactions similar to other Covid-19 shots such as fever that occur when the immune system is revved up.

While it released few details, the company said there were no serious allergic reactions. But occasionally other Covid-19 vaccines trigger such reactions, which can be reversed if promptly treated – and authorities have warned people to be on the lookout regardless of which type of vaccine is used.

J&J had hedged its bets with a study of a two-dose version of its vaccine, which is still underway.

Friday's interim results come on the heels of another vaccine in final testing. Novavax reported this week that its vaccine appears 89 per cent effective in a UK study and that it also seems to work — though not as well — against new mutated versions of the virus circulating in Britain and South Africa. A larger study in the US and Mexico is still enrolling volunteers.

Wall Street appeared dissatisfied with J&J's results, with shares dropping 4.2 per cent in early trading, a rare big drop for the world's biggest maker of health care products. Shares were down $4.07, or 2.4 per cent, at $165.09 in mid-morning trading.

In contrast, tiny Novavax saw shares skyrocket, jumping 71 per cent to $229.72 in mid-morning trading.

- AP