Vaccine makers AstraZeneca and Johnson & Johnson are poised to release safety and efficacy data from late-stage trials as early as January, federal health officials say. Yet there are already signs that AstraZeneca’s shot could fall well short of existing vaccines from Moderna and Pfizer. Early data released in November showed the AstraZeneca vaccine was just 62 percent effective at the intended dose.

Scientists and public health experts worry that consumers, faced with one option that is markedly different from others, could refuse a less-effective vaccine — even if that is the only one available to them. Polls show that nearly 40 percent of U.S. adults are hesitant to take any Covid-19 vaccine. Anything that reinforces that hesitancy could threaten the country’s ability to reach herd immunity and bring the pandemic to an end.

“Nobody is going to want [the AstraZeneca] vaccine compared to the Pfizer and Moderna vaccines” if its efficacy stays at the 62 percent mark in final trial data, said Angela Rasmussen, a virologist at the Georgetown Center for Global Health Science and Security.