If regulators give the go-ahead as expected in the next few days, there will be three vaccines available in the United States to prevent COVID-19.
A fourth is in widespread use in 50 countries around the world.
So, which shot should you get?
"Get the first vaccine you can," said Kathleen Neuzil, director of the University of Maryland Center for Vaccine Development and Global Health. "That's what I tell my family. They're all good."
The numbers vary somewhat on how well they all work, and new variants of the coronavirus that causes COVID-19 complicate the picture.
But for what matters most — keeping people from dying or going to the hospital — experts say they all do the trick.
Newcomer
Advisers to the U.S. Food and Drug Administration (FDA) will meet Friday to discuss the vaccine from health care giant Johnson & Johnson. The FDA is not required to follow their recommendation, but nearly always does.
Two other vaccines are already in widespread use in the U.S. from drug companies Moderna and Pfizer-BioNTech. A shot from AstraZeneca and the University of Oxford is in use in Britain, Europe, South Asia, Brazil, Mexico and elsewhere.
Johnson & Johnson's clinical trial data does not look quite as impressive on paper as the others available in the United States. It was about 66% effective against infections that caused from moderate to severe illness.
The Moderna and Pfizer-BioNTech vaccines both reported about 95% overall efficacy. But experts caution that the studies are not measuring quite the same thing and should not be directly compared.
The most important thing, Neuzil said, is how well all of the shots work against the most serious cases and death.
"That is what's keeping us in lockdown. That's what's filling up our hospitals," she said. "If we can prevent severe disease, or change severe disease to mild disease, we will be much closer to normalcy."
On that score, all of the vaccines excel. No one who received any of the four vaccines in any of the clinical trials died of COVID-19. There were no severe cases in the Moderna or AstraZeneca trials, and just one in the Pfizer study.
Variants
There were a handful of severe cases in the Johnson & Johnson trial. The shot was 85% effective against them.
However, unlike the Moderna and Pfizer-BioNTech vaccines that came out in December, the Johnson & Johnson shot had to contend with a more contagious variant that first appeared in South Africa.
It is not clear how well the Moderna and Pfizer-BioNTech vaccines work against the new variant. They do not work as well in test tube studies, but scientists are not sure whether that translates into lower protection for people.
More spreadable variants have also popped up in Brazil, Britain, the United States and elsewhere, worrying scientists worldwide. But experts do not think the mutations have rendered the vaccines useless.
One small study in South Africa raised concerns. It found that the AstraZeneca shot failed to prevent most infections with the new strain. The South African government scaled back plans to roll out the vaccine as a result.
But the study did not look at severe illness or death. Many scientists say the vaccine probably does still prevent the worst forms of the disease. Researchers are studying that now.
The World Health Organization still backs the AstraZeneca shot. It makes up the vast majority of doses delivered through COVAX, the WHO-backed program, to distribute vaccines equitably.
Real world
Elsewhere, real-world results are starting to come in from countries that have been using the vaccines for several weeks, and they all look promising.
A study in Israel found that protection from the Pfizer-BioNTech shot started to kick in about two weeks after the first shot. The vaccine was already 62% effective in preventing severe illness. After the second shot, it rose to 92% effective.
Hospitalizations fell by half among patients in a four-state study in the United States who received either the Pfizer-BioNTech or the Moderna shot. But those figures probably understate how well the vaccine works, because most of the vaccinated patients who were hospitalized had only received their first shot. The study has not yet been reviewed by other experts.
"It's a pleasant surprise" how well the vaccines are working, said study co-author Venky Soundararajan, co-founder and chief scientific officer of the data analysis firm nference.
The AstraZeneca-Oxford vaccine, which struggled in South Africa, excelled in Scotland. It was 94% effective at keeping people out of the hospital after just one dose in a study that has not yet been reviewed by outside experts.
The bottom line?
"Get the vaccine you can," Neuzil said, and not just to protect yourself. "The more people that are vaccinated, the more we are all protected, because we're protected by each other, as well."
