By LAURAN NEERGAARD and LINDA A. JOHNSON

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 U.S. and seven other countries, the single-shot vaccine was 66% effective overall at preventing moderate to severe illness, and much more protective — 85% — against the most serious symptoms.

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

“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% 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 U.S. government’s vaccine initiative.

The company said within a week, it will file an application for emergency use in the U.S., and then abroad. It expects to supply 100 million doses to the U.S. 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 U.S. 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 hospitalization 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 2 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% 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?

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 hospitalizations and deaths plus mutant versions of the virus sweeping some countries.

Dr. Anthony Fauci, the top U.S. infectious disease official, called that a messaging challenge — because the priority is to protect people from hospitalization 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 recognize 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% effective although there are questions about how much protection older adults get. An ongoing U.S. 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% 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% effective in a U.K. 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 U.S. and Mexico is still enrolling volunteers.

Wall Street appeared dissatisfied with J&J’s results, with shares dropping 4.2% 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%, at $165.09 in mid-morning trading.

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

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

By EMILY WANG FUJIYAMA

WUHAN, China (AP) — A World Health Organization team emerged from quarantine in the Chinese city of Wuhan on Thursday to start field work in a fact-finding mission on the origins of the virus that caused the COVID-19 pandemic.

The researchers, who were required to isolate for 14 days after arriving in China, left their quarantine hotel with their luggage — including at least four yoga mats — in the midafternoon and headed to another hotel.

The mission has become politically charged, as China seeks to avoid blame for alleged missteps in its early response to the outbreak. A major question is where the Chinese side will allow the researchers to go and whom they will be able to talk to.

Yellow barriers blocked the entrance to the hotel, keeping the media at a distance. Before the researchers boarded their bus, workers wearing protective outfits and face shields could be seen loading their luggage, including two musical instruments and a dumbbell.

Hotel staff waved goodbye to the researchers, who were wearing face masks. The bus driver wore a full-body white protective suit. They drove about 30 minutes to a lakeside Hilton resort-like hotel.

Former WHO official Keiji Fukuda, who is not part of the team in Wuhan, has cautioned against expecting any breakthroughs, saying it may take years before any firm conclusions can be made about the virus’s origin.

“This is now well over a year past when it all started,” he said earlier this month. “So much of the physical evidence is going to be gone. The memories of people are imprecise and probably the physical layouts of many places are going to be different than they were.”

Among the places they might visit are the Huanan Seafood Market, which was linked to many of the first cases, as well as research institutes and hospitals that treated patients at the height of the outbreak.

It hasn’t been disclosed whether they will leave Wuhan. One possible source of the virus is bats in caves in rural Yunnan province, about 1,600 kilometers (1,000 miles) southwest of Wuhan.

Foreign Ministry spokesperson Zhao Lijian said the experts would have talks, visits and inspections in China to carry out virus-tracing exchanges and cooperation. He did not provide any details.

The mission only came about after considerable wrangling between the two sides that led to a rare complaint from the WHO that China was taking too long to make the final arrangements.

China, which has strongly opposed an independent investigation it could not fully control, said the matter was complicated and that Chinese medical staff were preoccupied with new virus clusters in Beijing, Shanghai and other cities.

While the WHO was criticized early on, especially by the U.S., for not being critical enough of the Chinese response, it recently accused China and other countries of moving too slowly at the start of the outbreak, drawing a rare admission from the Chinese side that it could have done better.

Overall, though, China has staunchly defended its response, possibly out of concern over the reputational or even financial costs if it were found lacking.

Chinese officials and state media have also tried to cast doubt on whether the virus even started in China. Most experts believe it came from bats, possibly in southwest China or neighboring areas of Southeast Asia, before being passed to another animal and then to humans.

The origins search will try to determine where and exactly how that happened.

White House Press Secretary Jen Psaki expressed concern Wednesday about what she called “misinformation” coming out of China, adding that the U.S. supports a robust international investigation.

“It’s imperative that we get to the bottom of the early days of the pandemic in China,” she said.

Zhao responded that any negative speculation and politicized interpretation of the mission is inappropriate.

“We hope the U.S. can work with the Chinese side in a responsible manner, respect facts and science, and respect the hard work of the international expert team in tracing the origin of the virus,” he said, “so that they can conduct scientific research on the virus tracing without any political interference.”

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Associated Press photographer Ng Han Guan contributed to this report.