By Arthur Allen and Liz Szabo, Kaiser Health News

When getting vaccinated against Covid-19, there’s no sense being picky. You should take the first authorized vaccine that’s offered, experts say.

The newest Covid vaccine on the horizon, from Johnson & Johnson, is probably a little less effective at preventing sickness than the two shots already being administered around the U.S., from Pfizer-BioNTech and Moderna.

The Food and Drug Administration authorized the Johnson & Johnson vaccine after reporting it showed about 66% effectiveness at preventing Covid illness in a 45,000-person trial. No one who received the vaccine was hospitalized with or died of the disease, according to the data released by the company and FDA. As many as 4 million doses could be shipped out of J&J’s warehouses beginning this week.

The J&J vaccine is similar to the shots from Moderna and Pfizer-BioNTech, but uses a different strategy for transporting genetic code into human cells to stimulate immunity to the disease. The Moderna and Pfizer-BioNTech vaccines were found in trials last fall to be 94% effective in preventing illness caused by Covid. They also prevented nearly all severe cases.

But the difference in those efficacy numbers may be deceptive. The vaccines were tested in different locations and at different phases of the pandemic. And J&J gave subjects in its trial only one dose of the vaccine, while Moderna and Pfizer have two-dose schedules, separated by 28 and 21 days, respectively. The bottom line, however, is that all three do a good job at preventing serious Covid.

“It’s a bit like, do you want a Lamborghini or a Chevy to get to work?” said Dr. Gregory Poland, director of the Mayo Clinic’s Vaccine Research Group, who was a paid consultant in the J&J study. “Ultimately, I just need to get to work. If a Chevy is available, sign me up.”

“From a personal and public health perspective, the best advice for now is to get whatever you can as soon as you can get it, because the sooner we all get vaccinated the better off we all are,” said Dr. Norman Hearst, a family doctor and epidemiologist at the University of California-San Francisco.

Of the 10 people who got severe disease in the Pfizer trial, nine had received a placebo, or fake vaccine; none of the 30 severe cases in the Moderna trial occurred in people who got the true vaccine. A month after receiving the Johnson & Johnson shot there were no deaths or hospitalizations in those who had been vaccinated.

“The real goal is to keep people out of the hospital and the ICU and the morgue,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia. “This vaccine will do that well.”

J&J Vaccine Tested Against Variants

The data that Moderna and Pfizer-BioNTech presented to the FDA for their vaccines came from large clinical trials that took place over the summer and early fall in the United States. At the time, none of the new variants of Covid — some of which may be better at evading the immune responses produced by vaccines — were circulating here.

In contrast, the J&J trial began in September and was put into the arms of people in South America, South Africa and the United States. The J&J vaccine was 72% effective against moderate to severe Covid in the U.S. part of the trial, compared with 57% in South Africa, where a more contagious mutant virus is the dominant strain.

The Moderna and Pfizer-BioNTech vaccines might not have gotten the same sparkling results had they been tested more recently — or in South Africa.

“This vaccine was tested in the pandemic here and now,” said Dr. Dan Barouch, a Harvard Medical School professor whose lab at the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston developed the J&J vaccine. “The pandemic is a much more complex pandemic than it was several months ago.”

The J&J vaccine appears to have some other advantages. First, it seems to cause fewer serious side effects like the fever and malaise suffered by some Pfizer-BioNTech and Moderna vaccine recipients. High fever and dehydration are particular concerns in fragile elderly people who “have one foot on the banana peel,” said Dr. Kathryn Edwards, scientific director of the Vanderbilt Vaccine Research Program. The J&J vaccine “may be a better vaccine for the infirm.”

Many people may prefer the J&J shot because “it’s one and done.” It’s easier for administrators too: just one appointment to schedule.

The J&J vaccine can also be stored in regular refrigerators, while the Pfizer and Moderna vaccines have to be stored in freezers and must be used or discarded within six hours after the vial is opened. Vials of the J&J vaccine can be restored in a refrigerator for later use if doses remain.

“Right now we have mass immunization clinics that are open but have no vaccine,” said Offit. “Here you have a single-dose regime with easy storage and handling.”

Ultimately, a person’s address — not their personal preference — may determine which vaccine they receive, said E. John Wherry, director of the Institute for Immunology at the University of Pennsylvania’s Perelman School of Medicine. He pointed out that the Johnson & Johnson vaccine is a simpler choice for rural areas.

“A vaccine doesn’t have to be 95% effective to be an incredible leap forward,” said Wherry. “When we get to the point where we have choices about which vaccine to give, it will be a luxury to have to struggle with that question.”

Kaiser Health News is a nonprofit news service covering health issues. It is not affiliated with Kaiser Permanente.