Q&A: Johnson & Johnson COVID-19 vaccine

Only a single shot, compared to the other vaccines, by Moderna and Pfizer-BioNTech, which each require two shots.

Unlike the two other approved vaccines, the J&J vaccine doesn’t require ultracold storage: for at least three months, the vaccine can be stored at temperatures of 36°F to 46°F.

Not needing to store the vaccine in ultra cold or to schedule a booster shot expands the speed at which the population can be vaccinated as well as shortens how long it will take for the population to achieve herd immunity. Adding a third approved vaccine — and a third manufacturer — means more people can be vaccinated, too. New York City plans to use the vaccine to inoculate homebound seniors and others who can’t make it to a vaccine site, the de Blasio administration has said.

On Friday, an expert panel unanimously recommended that the U.S. Food and Drug Administration approve the shot, a step that is all but certain, according to The Washington Post.

Yes, such as one by the firm Novavax, a two-shot regimen that injects a synthesized and slightly modified version of the spike protein — spikes, or "coronas," are how the virus attacks the human body — using a commonplace insect virus; in it are DNA instructions to make the spike protein, according to The Wall Street Journal. The Novavax vaccine is advancing toward authorization, the Journal said.

The other vaccines work by injecting messenger RNA, a molecular road map, to prompt the body to produce coronas — spiked proteins — the kind the virus itself would use to attach to human cells. There is no virus in those vaccines. The J&J vaccine adds the gene for the coronavirus' spiked proteins to another virus, called adenovirus, which typically causes flu-like symptoms or colds, according to The New York Times. The adenovirus is modified so it enters cells but doesn't replicate inside them or cause disease.

The efficacy rate is up to 72% in the United States. The vaccine is 66% effective overall in preventing moderate to severe COVID-19 after 28 days, 85% overall in preventing severe disease, and completely effective in preventing COVID-19-related hospitalization, the company said in a Jan. 29 news release. Although the other vaccines are as much as 95% effective in preventing COVID-19, Dr. Mitch Katz, head of the New York City public hospital system, said Thursday that it’s not worth foregoing a J&J vaccine for Moderna’s or Pfizer’s: "Absolutely, what we, as doctors, as New Yorkers care about is preventing serious hospitalization and deaths, and the Johnson & Johnson vaccine is every bit as good as the Pfizer and Moderna at preventing those serious outcomes. And the fact that it's a single dose and that it does not need special refrigeration will make it so easy."

The most common side effect — pain in the injection site, in about half of all recipients, was followed by headache (38.9%), fatigue (38.2%) and muscle pain (33.2%), according to an FDA briefing document dated Friday.