The Johnson & Johnson one-dose vaccine received FDA authorization on Feb. 27. Photo through Maurice Ramirez

Editor"s Note: This story was updated might 7 to include new information top top the risk of blood clots.

With the FDA’s emergency usage authorization the the Johnson & Johnson vaccine on Feb. 27, the U.S. Now has three highly efficient vaccines versus COVID-19.

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All 3 vaccines – Johnson & Johnson, Pfizer, and Moderna – totally prevented hospitalizations and deaths in clinical trials, i beg your pardon is why public health experts are recommending that world get the first vaccine the is available to them. However the vaccines differ in a number of details of just how they work and also how they to be studied, resulting in questions and also some confusion.

We request UC san Francisco infectious disease expert Monica Gandhi, MD, MPH, to unpack several of the big questions around vaccine science, such as how the Johnson & Johnson vaccine differs, just how well the works against the brand-new variants, and whether you must be worried about transmitting the virus after ~ vaccination.

Use that the Johnson & Johnson (J&J) vaccine has actually resumed ~ a pause recommended by the FDA and also CDC in bespeak to examine reports of severe blood clots. What room the threats of this rare side effect?

As of may 6, 2021, 16 situations of this blood clots have actually been reported amongst a complete of around 8 million human being who got the J&J vaccine. The unusual problem is known as thrombosis (blood clot) v thrombocytopenia (low platelet count), or TTS, which usually occurs in ~ a rate of around one in a million per year in the general population. Amongst those who have received the J&J vaccine, the price is around two in a million. The is top top par with the price of anaphylaxis, a major allergic reaction, that has been reported for the mRNA vaccines, about 2.5 per million.

The risk appears to be higher in younger women: 15 that the confirmed instances have remained in women, and 13 of this in women ages 18 come 49. Amongst women periods 18 come 49, the hazard of TTS after ~ the J&J vaccine is about seven in a million.

“So that does placed the hazard in context, in the feeling that that is still exceptionally low,” claimed Gandhi.

TTS likewise has been reported after ~ the AstraZeneca vaccine in Europe, but it’s no yet clean in either situation how the vaccines may be bring about these blood clots. Similarities with an autoimmune problem known together heparin-induced thrombocytopenia (HIT) suggests the human body is creating antibodies against its own platelets.

Are there civilization who should avoid acquisition the J&J vaccine?

The FDA has included a warning around TTS in that is emergency usage authorization of the J&J vaccine however has not minimal its use. “I think the prudent to put a warning brand on it,” said Gandhi. “The warning label helps patient to speak through their doctor around the blood clot risk and also helps medical professionals to be alert to such occurrences.”

The reported cases of TTS have developed one to two weeks ~ the J&J vaccine and also most often have associated blood clots in the veins that the brain, but additionally elsewhere in the body. The symptoms to watch out for incorporate severe headache, earlier pain, abdominal pain, blurry vision and also other neurological symptoms. The condition can it is in monitored and also treated, stated Gandhi.

Gandhi claimed she has not advised her very own patients against taking the J&J vaccine, other than a few younger females who space on oral contraceptives, which currently increases the hazard for blood clots. For those patients, she proposal the mRNA vaccines.

Overall, Gandhi stated the pause has actually not decreased her enthusiasm because that the J&J vaccine. “It’s a very effective vaccine,” she said, “And ns think it’s an essential vaccine for the world, specifically when we see what’s going on in India right now.”

The reality remains that ongoing use that the J&J vaccine will mitigate hospitalizations and also deaths. “I keep coming ago to how an extremely rare TTS is and how very common COVID is,” stated Gandhi. “You placed together your risk versus benefit analysis and it’s much an ext common to it is in exposed come COVID 보다 it is come this an extremely rare side effect.”

How walk the J&J vaccine work? how is the organic mechanism various from the of the mRNA vaccines?

All 3 vaccines job-related by prompting your own cells to produce the spike protein – the protrusions ~ above the coronavirus that enable it strike human cells – so her immune mechanism learns to recognize and also respond easily to a genuine infection.

Unlike the mRNA vaccines indigenous Pfizer and also Moderna, which supply fat-covered bits of genetic material into your cells, the Johnson & Johnson vaccine offers a “shell of a virus” to carry genetic material into your cells, said Gandhi. The “shell” is one adenovirus, which normally reasons colds, but has been modified so that it can no much longer replicate and also make you sick.

The genetic material in the mRNA vaccines is RNA, vice versa, the hereditary material in the J&J vaccine is DNA, however both encode the info to make the spike protein that SARS-CoV-2.

Johnson & Johnson vaccine sheep being all set at the City university vaccination site in mountain Francisco. Photo by Maurice Ramirez

“Inside the adenovirus is the DNA that your human body will usage to make into RNA and then right into the spike protein the the coronavirus,” stated Gandhi. She noted that the DNA and RNA then quickly degrade in the person body and do not have the capability to affect our chromosomes.

Once her cells make the spike protein, all 3 vaccines occupational similarly. “The spike protein no look favor anything in our human body,” said Gandhi. “So, girlfriend raise one immune solution with T cells and antibodies to that spike protein, and that enables you come fight the virus if you ever see that in the future.”

This form of adenovirus modern technology has been offered in an Ebola vaccine but is still fairly new. “It’s an ext familiar than mRNA technology, but I wouldn’t say it is the most familiar an innovation either,” stated Gandhi.

Why is the J&J vaccine just one dose? Is it feasible that it could eventually end up being two doses or that the mRNA vaccines could come to be one dose?

The J&J vaccine went into Phase III trials together a one-dose vaccine because earlier step trials had shown solid immune responses after just one dose, said Gandhi. “After one dose, throughout all populations, also in enlarge people, the antibody an answer and T-cell response were excellent and increased over time.”

J&J is at this time conducting a trial to give world two doses, i beg your pardon may boost efficacy versus mild and moderate disease, stated Gandhi.

Gandhi also detailed that the J&J vaccine continues to boost in efficacy after two weeks, the present CDC-recommended waiting period after vaccination. Immunogenicity data native the phase I/II trials imply the immune solution may proceed to improve even after 28 days. “I carry out think it’s going to have even an ext efficacy after four weeks,” claimed Gandhi. “I call it the gift that keeps ~ above giving.”

For the mRNA vaccines, the immunogenicity data after ~ one sheep did no look together powerful, so the step III trials were conducted with two doses. Although some real-world data says that one dose may likewise offer great protection, Gandhi claimed there is not enough information come recommend acquiring only one sheep of the mRNA vaccines.

Some human being are pertained to that the as whole efficacy of the J&J vaccine – 66 percent globally, 72 percent in the U.S. – is reduced than the 94-95 percent reported because that the mRNA vaccines. Have the right to you put this difference in context?

“The method I think about these vaccine trials is come look at the worst outcomes first – hospitalizations and deaths indigenous COVID-19 – because that’s what gained us into trouble to begin with,” claimed Gandhi.

In the J&J trial, the placebo team had 16 hospitalizations and seven deaths native COVID-19, whereas the vaccine team had none, which method the vaccine detailed 100 percent efficacy versus hospitalizations and deaths.

For serious disease, i m sorry includes human being who to be sick enough with COVID-19 to require clinical intervention but recovered without hospitalization, the efficacy was around 85 percent across the board in Brazil, south Africa and also the U.S.

Including mild and also moderate disease, the overall efficacy was 66 percent, however varied across the regions: 72 percent in the U.S., 64 percent in southern Africa, and 61 percent in Brazil. “Mild and also moderate outcomes” could include a selection of illness, said Gandhi, and we won’t recognize the details till the full trial outcomes are published, yet we do recognize that everyone recovered without medical intervention.

“Admittedly, versus mild to moderate disease, that didn’t work-related as well, and also I understand people’s concerns,” said Gandhi.

Cars inside wall up in ~ the the City university drive-through vaccination site in san Francisco. Photo through Maurice Ramirez

Yet she stated that on a population level, the availability of a one-dose vaccine deserve to really rate up inoculations and aid bring total instances down. She pointed to the unified Kingdom, which has actually rolled-out a similar adenovirus vaccine, do by AstraZeneca, that protects versus severe disease, hospitalizations and also deaths an extremely well yet is less effective versus mild and also moderate disease. Return the AstraZeneca vaccine is two doses, the UK has actually chosen to offer the sheep 12 weeks apart in order come vaccinate an ext people – a "one-dose-first" strategy that has been very effective, stated Gandhi.

“Their hospitalizations and also cases room plummeting much faster just since they have more vaccine supply. Their outcomes have actually been phenomenal,” said Gandhi. “So once I look at that, ns think, ‘Oh, I can quibble all i want around the clinical trial, yet the real civilization is the real world.’”

What carry out we know about each vaccine’s ability to protect against the variants?

We know an ext about exactly how the J&J vaccine protects versus the coronavirus variants due to the fact that the trials were carried out in south Africa and Brazil as soon as the brand-new variants had come to be prevalent. In south Africa, some 95 percent of circulating virus was the B.1.351 variant and in Brazil, 69 percent that the circulating virus to be a P1/P2 different at the moment of the trial. Back the J&J vaccine showed up to be less effective versus mild and moderate condition in this regions, it stayed strongly protective versus severe disease, hospitalizations and deaths.

“We can not say definitively that the distinction in efficacy in these areas is early out to more variants, but it’s one assumption,” said Gandhi.

In the U.S., whereby the pervasiveness of variants was low, the overall efficacy the 72 percent most likely was not affected by the variants, claimed Gandhi.

In contrast, the mRNA vaccine trials to be not performed in the existence of high level of the variants, so less is known about how well they protect versus the variants. Real-world data from Pfizer vaccinations imply they room effective versus the B.1.1.7 variant originally detected in the U.K.

What execute we know about each vaccine’s capacity to protect against asymptomatic infection?

We also have much more information about asymptomatic infections from the J&J trials since they had asymptomatic PCR testing and antibody testing. (Participants were tested for antibodies to a component of SARS-CoV-2 the was no the spike protein because the vaccine would induce antitoxin to the spike protein.) The vaccine was found to it is in 74 percent effective against asymptomatic infection, similar to that is protection against symptomatic infections.

The mRNA vaccine trials did no look for asymptomatic infections, yet Gandhi thinks all the vaccines most likely offer parallel protection against symptomatic and asymptomatic infections. “They didn’t perform this sort of testing, but based upon the real-world data native vaccine roll-out, the seems most likely your protection versus asymptomatic epidemic will most likely mirror your protection against symptomatic infection,” she said.

A research of U.K. Health treatment workers, because that example, found that the Pfizer vaccine diminished all infections, consisting of asymptomatic, by 86 percent. A real-world research of the general populace in Israel uncovered that the Pfizer vaccine decreased asymptomatic epidemic by 94 percent. Another study, among pre-surgical patients throughout the mayo Clinic system, confirmed that mRNA vaccines to be 80 percent protective against asymptomatic infections.

Were there various other differences in between the vaccine trials?

Compared come the mRNA vaccine trials, the J&J vaccine attempt included more participants who figured out as Hispanic/Latino (45.1 percent) and Black or african American (17.2 percent). It also included much more participants that were end 60 years old (34.6 percent) and an ext who had actually comorbidities (39.9 percent).

The much more diverse participants no only help to far better determine vaccine efficacy but likewise “enhances trust amongst the populations that look prefer the populations who space enrolled,” said Gandhi.

If she somewhat much less protected versus mild and moderate COVID-19 with the J&J vaccine, go that mean you are more likely to transmit the virus? must your habits depend on which vaccine girlfriend get?

No vaccine have the right to prevent all COVID-19 infections. To minimization the chances of transmitting the virus also after you’ve been fully vaccinated, Gandhi suggests avoiding call with unvaccinated human being if girlfriend experience feasible COVID-19 symptoms.

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The an excellent news is the vaccination appears to mitigate viral load in the tiny percentage of civilization who still become infected. Preliminary data from Israel of the Pfizer vaccine suggest that if you capture COVID-19 after ~ vaccination, you’re most likely to harbor much less virus, making you much less likely to transmit.

“I think the going to become quite difficult to transmit virus after you’ve been vaccinated, even if you are exposed, due to the fact that of the short viral fill in your nose,” claimed Gandhi. “Which is just one of the factors the CDC has actually said the vaccinated human being do not should quarantine after ~ exposure if asymptomatic. That’s really based on that data.”