This Dec. 2, 2020 photo provided by Johnson & Johnson shows vials of the COVID-19 vaccine in the United States. The nation is poised to get a third vaccine against COVID-19, but health officials are concerned that at first glance the Johnson & Johnson shot may not be seen as equal to other options from Pfizer and Moderna. (Johnson & Johnson via AP)
New single-dose vaccine cleared for national rollout
02:21 - Source: CNN
CNN  — 

And then there were three.

There are now three Covid-19 vaccines authorized for emergency use by the US Food and Drug Administration, manufactured by Pfizer/BioNTech, Moderna and Johnson & Johnson. All three will be distributed across the United States.

Many people are wondering which Covid-19 vaccine they should get: Is one better for certain groups of people? Given how many people still can’t get any vaccine, will people have a choice? If so, which vaccine should they choose?

We asked CNN Medical Analyst Dr. Leana Wen for her advice. Wen is an emergency physician and visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health.

Wen is also a volunteer participant in the Johnson & Johnson clinical trial, though she doesn’t know yet whether she received the vaccine or placebo.

CNN: Can you explain the differences between the three FDA-authorized vaccines? What do we know about their safety and efficacy?

Dr. Leana Wen: The vaccines from Pfizer and Moderna were authorized first, back in December. They are similar to one another in that they are both developed using the mRNA platform. The Johnson & Johnson vaccine has just been authorized. It uses a different way of stimulating an immune response, with an inactivated cold virus. The Pfizer and Moderna vaccines both require two shots. Johnson & Johnson has just been authorized as a one-dose vaccine.

All three vaccines have very favorable safety profiles, meaning that they are all very safe, when tested in tens of thousands of people. All three are virtually 100% in clinical trials at preventing hospitalizations and deaths, which is the endpoint that we really care about.

A health care worker administers the Moderna Covid-19 vaccine at the Bible-Based Fellowship Church on February 13 in Tampa, Florida.

The Pfizer and Moderna vaccines appear to be more effective at preventing mild to moderate disease, about 95%. The Johnson & Johnson vaccine is about 72% effective, based on US trials. However, these results should not be compared directly, because the trials were not done as head-to-head comparisons.

CNN: Why not? You can see why people would look at those numbers and say, 95% versus 72%? I’ll take the one that’s 95%.

Wen: This is an understandable concern. Here are three reasons why this is not the right comparison.

First, the vaccines were studied at different time periods. The Pfizer and Moderna studies were done before these more concerning variants became a major factor. Also, there wasn’t as widespread disease at the time those trials were run. We don’t know what their efficacy would be if they were studied under the same conditions as the Johnson & Johnson vaccine, or vice versa. That’s why we say that these are not head-to-head comparisons and can’t be weighed one directly against another.

Second, one the main locations where the Johnson & Johnson vaccine was studied was South Africa, where the predominant variant at the time of the study was the B.1.351 variant. There is substantial concern that none of the vaccines we have may work as well against this variant.