Johnson & Johnson's Covid-19 vaccine could protect millions more Americans from contracting the coronavirus. The key will be assuring people that the single-shot vaccine is worth taking, as its overall efficacy appears lower than the two-dose ones already on the market in the U.S. J&J's shot, which U.S. regulators authorized Saturday, is more convenient than the vaccines cleared by the Food and Drug Administration last year. It requires one injection and can be stored for months in a refrigerator. State health officials and the Biden administration see it as a way to quickly host mass clinics as more transmissible virus variants continue to spread. Yet the ease of distributing the vaccine will need to be balanced with the risk of creating the perception that J&J's shot is an inferior option. At first blush, J&J's formula looks less effective than the vaccines from Pfizer Inc.-BioNTech SE and Moderna Inc. It was found to be 72% effective in preventing moderate-to-severe Covid-19 cases in the U.S., and 66% effective globally. Pfizer-BioNTech and Moderna respectively touted 95% and 94% efficacy in preventing symptoms of the disease. Yet it's impossible to directly compare results. J&J conducted the largest Covid-19 vaccine trial to date, including at dozens of sites in South Africa and Brazil, pitting its vaccine against mutant strains of the virus that the earlier vaccines weren't tested against. The 43,000-plus participant study began enrollment in September and reported results in late January. Cases were accrued at the pandemic's peak globally. "This is not the time to be quibbling over decimal places or the levels of efficacy that we're seeing," said Michelle Williams, an epidemiologist and dean of the Harvard T.H. Chan School of Public Health. Her message is clear: Vaccines are a public health tool meant to keep people from getting sick, becoming hospitalized, and overwhelming the health-care system. Simple Messaging That's precisely what J&J's vaccine does. Across all regions, including places where more transmissible variants have spread, the single shot was 85% effective in preventing severe disease after 28 days. Further, it demonstrated complete protection against all Covid-related hospitalizations and deaths. H. Cody Meissner, a pediatric infectious disease specialist at the Tufts Medical Center in Boston and an independent adviser to the FDA, said public health authorities shouldn't prefer one vaccine over another. "It's important that people do not think that one vaccine is better than others," he said Friday during a public meeting after which the panel unanimously recommended that the FDA authorize the J&J shot. "All vaccines work with what appears to be equal efficacy and equal safety as of this time." Simplicity in messaging will be essential, said Glen Nowak, director of the Center for Health and Risk Communication at the University of Georgia. Health officials should stick to the main talking point: All three vaccines protect people against the strains of the virus currently circulating and causing illness and death in the U.S. "When you start to communicate complexity and nuance, you lose people," Nowak said. The Biden administration already is trying to boost confidence in the J&J vaccine, acknowledging concerns that some people may skip it and instead try to get the Pfizer-BioNTech or Moderna vaccines. "The vaccine that's available to you -- get that vaccine," Anthony Fauci, the U.S.'s top infectious-disease official, said during a briefing on Friday. "It is important to get as many people vaccinated as quickly and as expeditiously as possible." A February survey found only 7% of people wanted a single-dose vaccine, compared with 58% who said they prefer a two-dose series, according to a presentation Sunday to the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices. About one in five said they would take either. Of those who said they want a two-dose shot, 28% said they would take a single-shot option rather than wait a month to get another one. The survey was conducted before all of the data on J&J's vaccine became available, which could affect attitudes. Complicating matters, J&J is testing a two-shot version of the vaccine, suggesting that it thinks adding a second shot could improve protection. At the advisory panel hearing on Friday, the company's researchers faced questions from experts on whether people who received the one-shot version would need to get a second dose several months later, should the two-shot version perform better in trials. Easier Shot The Biden administration will start shipping 3.9 million J&J doses to the states this week, immediately accelerating the immunization campaign. A total of 20 million are promised by the end of March, and 100 million by the end of June. With J&J's vaccine, the nation's immunization campaign will move swiftly. "A one-dose vaccine decreases the burden on the health-care system," while simultaneously lowering the cost of administering the vaccine, Gregory Poland, a virologist and director of the Mayo Clinic's Vaccine Research Group, said Friday during the FDA advisory meeting. The vials, which each hold five doses, don't need to be diluted with another substance before being administered like the Pfizer-BioNTech vaccine. Also, they can be stored at temperatures the average refrigerator or cooler can handle, so providers won't need to wait as they thaw. These attributes lend themselves to better serving communities that may not have the ultra-cold freezers needed to store Pfizer's formula. Plus, a one-shot vaccine opens up possibilities for more easily immunizing people who may be hard to reach or face barriers like transportation. Fauci has pointed to rural areas or those where it has been difficult to get people to return for a second dose as good places for J&J's shot. Doctors' offices could end up administering the vaccine as it doesn't have special freezer requirements, a CDC reviewer said Sunday during an emergency meeting of the agency's immunization advisory panel. Utah envisions immunizing people with the J&J vaccine at mobile clinics and inoculating the homeless, those without insurance and agricultural workers, among other groups. North Carolina anticipates J&J's vaccine could be used to immunize people who can't take two days off work for two doses. Currently, the shot is authorized for those ages 18 and older. J&J will soon be launching a adolescent trial, in hopes of expanding its use to children. Balanced Approach The benefits also carry risk. Targeting any one group, especially vulnerable populations, could inadvertently create the impression of a nefarious agenda, said Williams of Harvard. This will be an especially delicate balance among Black communities that are wary of any experiments that could recall the infamous Tuskegee study where government scientists withheld syphilis treatment to Black men for research purposes. Virginia officials are concerned about this possibility, said Danny Avula, the state's vaccine coordinator. The state plans to funnel most of the 68,000 doses of J&J's vaccine it's set to receive this week to mass vaccination sites, with the idea that the shots will be available to people from all backgrounds in all parts of the state. "We don't ever want there to be something that the public questions, especially given over the last year how much distrust of government has grown," he said, even if that means sacrificing ease in rural parts of the state. Some people might actually prefer the J&J vaccine. North Carolina officials have heard from residents who are holding out for one dose and one vaccine appointment, said Mandy Cohen, secretary of the state's Department of Health and Human Services, in an interview. The vaccine uses more familiar technology, possibly winning over people who are concerned about mRNA vaccines, Avula said. It's based on a common cold virus that doesn't replicate in the body, but prepares it for infection. North Carolina is trying to avoid brand names, Cohen said. Utah plans to stress the protection that all of the Covid-19 vaccines provide, said Rich Lakin, the state's immunization manager, in an interview. "Maybe we've become used to the 95% efficacy of Pfizer and Moderna and that's the new norm," Lakin said. "When in reality, J&J is still very effective in keeping people from becoming severely ill and hospitalized from Covid."