Two months after it first reached the arms of people in the United States, Johnson & Johnson’s COVID-19 vaccine is once again being administered following a 10-day pause over blood-clotting concerns. At the time of publication, over 8.7 million doses of the single-shot vaccine have been delivered so far, per the Centers for Disease Control and Prevention (CDC).
At the recommendation of the CDC and the Food and Drug Administration (FDA), the Johnson & Johnson COVID-19 vaccine was temporarily unavailable last month as the agencies investigated sporadic reports of a rare, potentially deadly blood-clotting disorder in six patients—all women between the ages of 18 and 48. Vaccinations resumed on April 23.
Unlike its mRNA, two-dose vaccine competitors from Pfizer-BioNTech and Moderna, this option uses a modified adenovirus to spur antibody production in its recipients. The Johnson & Johnson vaccine is about 66% effective at preventing symptomatic COVID-19, and 85% effective at preventing a severe or critical form of COVID-19 that can lead to hospitalization or death at least 28 days after vaccination, according to data released by the company, which was confirmed in an FDA analysis.
Because it requires just one dose and has manageable temperature storage requirements, Johnson & Johnson’s vaccine was providing a helpful boost to the U.S. immunization effort. President Biden confirmed that Johnson & Johnson worked with one of its competitors, pharmaceutical giant Merck, in a “historic partnership” to increase production of its vaccine, The Washington Post reported.
Here’s everything experts know about Johnson & Johnson’s vaccine, including how it works, its efficacy, and its side effects—plus how it compares to the other vaccines available in the U.S. so far.
How effective is the Johnson & Johnson COVID-19 vaccine?
The FDA’s approval is based on data from Johnson & Johnson’s global phase 3 clinical trial, which enrolled 43,783 people who were randomly given either a placebo or the Johnson & Johnson COVID-19 vaccine. The FDA’s analysis, which used data from 39,321 participants, found the Johnson & Johnson vaccine is about 66% effective at preventing moderate-to-severe COVID-19 at least 28 days after vaccination. When looking at data in the U.S. specifically, that number increases to about 74%.
What’s more, the vaccine is about 77% effective at preventing severe or critical forms of COVID-19 at least 14 days after vaccination, and 85% effective 28 days after vaccination. Its efficacy excels where it matters most: The company’s phase 3 trial reported no COVID-19-related deaths and no COVID-19 cases requiring medical intervention after 28 days in vaccinated participants.
The vaccine’s efficacy against moderate-to-severe COVID-19 did drop in South Africa—64% effective after 28 days—which is likely due to the highly infectious variant (B.1.351) dominating the region, says Richard Watkins, M.D., an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University.
Although Pfizer-BioNTech and Moderna both offer COVID-19 vaccines with 95% efficacy, all of the available vaccines offer strong, worthwhile protection, as all of them have been shown to protect against severe illness and death, the two worst outcomes, says Dr. Watkins. He says it is worth noting that “the flu vaccine is usually up to 60% effective,” and that annual shot plays an integral role in decreasing flu-related hospitalizations and deaths every year.
What’s really important with the vaccine is “not how well it protects against symptomatic disease, but how well it protects against severe disease,” says infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. These vaccines have been approved because they’re proven to work; once one becomes available to you, getting vaccinated will help protect you, your loved ones, and those who are most vulnerable.
How does the Johnson & Johnson COVID-19 vaccine work?
The Johnson & Johnson vaccine modifies an existing adenovirus, which usually causes colds, with the novel coronavirus’ spike protein, or the piece that latches onto human cells. The resulting adenovirus doesn’t have the ability to reproduce in the human body, meaning it can’t cause COVID-19 or any other illnesses.
When you get the Johnson & Johnson vaccine, the modified adenovirus is pulled inside your cells, where it travels to the cell nucleus, home to its DNA. The adenovirus then puts its DNA into the nucleus, the spike protein gene is read by the cell, and it’s then copied into messenger RNA, or mRNA. Your cells begin making spike proteins, which are then recognized by your immune system, causing your body to produce antibodies to the perceived threat.
Translation: It’s like a meet-and-greet between your immune system and COVID-19. Your body now knows how to produce antibodies for the illness, but without having to experience all of the side effects that come with a true coronavirus infection. The immune system remembers how to respond to the spike protein, and if you come into contact with it in the future, your body will have the capability to fight it more efficiently. However, it’s not yet clear how long this protection lasts or whether the vaccine prevents person-to-person transmission of the virus, per the FDA.
This technology is unique, but Johnson & Johnson has a lot of experience with it, as it’s already been used for its Ebola vaccine. “They’ve given hundreds of thousands of doses of this similar vaccine,” which has had no major safety issues, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. Other COVID-19 vaccines, like Oxford and AstraZeneca’s vaccine, use similar adenovirus technology.
Johnson & Johnson’s vaccine works differently than the mRNA vaccines available from Pfizer and Moderna, which both introduce a piece of genetic code that essentially tricks the body into producing COVID-19 antibodies, no actual virus required. In a way, these vaccines skip some of the steps that adenovirus-vectored vaccines take. Like Johnson & Johnson’s vaccine, Pfizer’s and Moderna’s options are the first of their kind.
What are the side effects of the Johnson & Johnson COVID-19 vaccine?
The vaccine was “generally well-tolerated” in study participants, Johnson & Johnson said in a press release. According to the data so far, the vaccine may cause “mild-to-moderate side effects typically associated with vaccinations,” similar to those expected from the Pfizer and Moderna vaccines. This includes cold-like symptoms, like a headache, body aches, pain at the injection site, and a fever—a normal sign that the body’s immune response is being primed.
But the CDC and the FDA investigated six reported cases of cerebral venous sinus thrombosis (CVST), a rare but severe blood clot that could cause potentially deadly brain hemorrhages in otherwise healthy patients. There is insufficient evidence to link CVST to the Johnson & Johnson vaccine, but experts paused the vaccine rollout to be safe and to ensure a thorough investigation.
Each of the six affected patients were women between 18 and 48, and all developed the condition within one to three weeks after receiving the Johnson & Johnson vaccine. One of the six women died from the disorder.
“Right now, these adverse events appear to be extremely rare,” the CDC and the FDA explained in a joint statement following the pause. “We are recommending a pause in the use of this vaccine out of an abundance of caution. This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot.”
Now that the main investigation has closed, both agencies once again recommend receiving the Johnson & Johnson vaccine—but with a clearer picture. “Women younger than 50 years old especially should be aware of the rare but increased risk of thrombosis,” the CDC explains. “There are other COVID-19 vaccine options available for which this risk has not been seen.”
The health agencies recommend that anyone who received the Johnson & Johnson vaccine monitor for severe headache, abdominal pain, leg pain, and shortness of breath within three weeks of vaccination. If these symptoms develop, contact your healthcare provider for proper diagnosis and treatment.
How is the Johnson & Johnson COVID-19 vaccine stored?
One of the biggest perks of the Johnson & Johnson vaccine is its durability. Because it doesn’t harbor delicate mRNA like the Pfizer and Moderna vaccines (which need to stay frozen), it’s much less fragile and can stay stable in a normal refrigerator between 36°F and 46°F for up to three months.
“That’s a big advantage,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. Safely storing the other available vaccines, particularly the Pfizer vaccine, which needs to be kept at a frigid -94°F, presents challenges for the average doctor’s office or pharmacy, as most locations don’t have specialty freezers that reach those temperatures.
The bottom line
Now that use of the Johnson & Johnson COVID-19 vaccine has resumed, it will only continue to bolster the U.S. immunization effort, getting us all closer to some sense of normalcy—and this time, both patients and doctors are more aware of the slight risks involved.
This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.
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