The panel voted 12 for the vaccine and none against, with one rejection.

The committee acted with little debate after presentations showed that at all clinical trial sites, the vaccine provides 85 percent protection against severe Covid-19 disease and complete protection against hospitalizations and deaths.

Late Sunday, Rochelle P. Walensky, the CDC director, signed the committee’s recommendation calling the new vaccine “another milestone towards an end to the pandemic.”

Experts pointed out that the Johnson & Johnson vaccine will be easier to sell than the other two vaccines that Moderna and Pfizer make with their German partner BioNTech. It only requires one shot instead of two and can be stored in standard refrigerators instead of freezers. Healthcare professionals have found it to be particularly good for remote areas and clinics, as well as for mass vaccination sites.

The committee weighed these benefits against the shot’s slightly lower rate of effectiveness in clinical trials. Pfizer and Moderna images were shown to each protect 95 percent against symptomatic Covid disease, while Johnson & Johnson’s at US trial sites were 72 percent effective against moderate to severe illness.

However, direct comparisons between the vaccines are problematic because the trials were carried out at different times in different locations. For example, Pfizer and Moderna vaccines were tested before new variants of the virus emerged in the UK, South Africa and elsewhere.

The panel, the Advisory Committee on Immunization Practices, reviewed a recent survey that found that choosing between a two-dose vaccine that is as effective as that of Pfizer or Moderna, or a single-dose vaccine that does so is as effective as that of Johnson & Johnson; only 7 percent of respondents selected Johnson & Johnson’s. Twenty-one percent said they would take both.

Importantly, of the 58 percent of respondents who said they preferred a vaccine like Pfizer or Moderna, nearly half said they took a vaccine like Johnson & Johnson instead of waiting a month for either of the other two.

The committee met almost exactly a year after the first death related to Covid-19 in the United States. The committee is expected to meet again on Monday and discuss all three vaccines, including how best to use them in different populations.