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CVS registered pharmacist Ken Ramey prepares to give a Covid-19 vaccine at the isles of Vero coast assisted and independent an elderly living neighborhood in Vero Beach, Fla.Wilfredo Lee/AP
This story was last updated on Nov. 11. 

Scientific teams roughly the people have developed successful Covid-19 vaccines in incredibly short order. In a feat that also a pair of years back would have seemed fully out the reach, vaccines come protect versus the new condition were gift used before the an initial anniversary that the disclosure that a brand-new threat existed. This is truly extraordinary.

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In the unified States, 3 vaccines are available. Two — those indigenous Moderna and Johnson & Johnson — have actually emergency use authorizations, i beg your pardon are green lights indigenous the Food and also Drug administration to be put into use, even though they have actually not yet been fully licensed. In august 2021, the FDA gave full approval come the vaccine emerged by the partnership of Pfizer and also German manufacturer BioNTech for world 16 and also older. This vaccine is offered in younger teens under an EUA and also is intended to be easily accessible for youngsters five and also older by the first week of November.

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The Pfizer shot an initial received emergency authorization in mid-December 2020, followed closely by the one developed by Moderna with help from the national Institute that Allergy and Infectious Diseases.

In so late February came a third. Janssen Pharmaceuticals, the vaccine division of Johnson & Johnson, secured an emergency use authorization because that its one-dose vaccine. The vaccine was viewed as a potential game-changer. That doesn’t call for the fussy cold-chain required to keep the Pfizer and also Moderna vaccines native spoiling. It is cheaper, both on a per-dose basis and because only one sheep is needed. Plus that was believed a one-and-done option might entice some people who couldn’t easily get two doses to role up your sleeves.

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But since the J&J vaccine’s come on the scene there have been a number of challenges. A manufacturing snafu in the hand of a contract production company contaminated 15 million doses, which had to it is in destroyed. And in mid-April, the FDA and also CDC recommended says pause use of the vaccine as they investigate even if it is the vaccine root cause a rare yet serious side result — the development of diffuse blood clots, also though the couple of individuals who emerged the problem had low platelet levels.

What complies with is a head-to-head comparison of the vaccines occurred by Pfizer and also BioNTech, by Moderna, and also by J&J. This short article will be updated as developments occur.

Vaccine types

The Pfizer and Moderna vaccines are made utilizing messenger RNA, or mRNA, a an innovation that it is intended a little bit of genetic code to cell — in effect, a cooking recipes to do the surface ar protein (known together spike) ~ above the SARS-2 virus. The protein made through the mRNA instructions activate the immune system, teaching it to watch the spike protein together foreign and also develop antibodies and other immune weapons with which to fight it.

The J&J vaccine supplies a different method to instruct human cells to make the SARS-2 spike protein, which climate triggers one immune response. It is what’s well-known as a viral vectored vaccine. A not authorised adenovirus — from a huge family the viruses, some of which reason common colds — has been engineered to bring the hereditary code for the SARS-2 spike protein. When the adenovirus start cells, they use that code to make spike proteins. J&J to work this same approach to do an Ebola vaccine that has been authorized for usage by the European drugs Agency.


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Target population

The Pfizer vaccine has actually been approved for usage for civilization aged 16 and older, despite its EUA additionally extends come children and teens age 5 come 15. Youngsters aged 12 come 15 are provided the adult sheep of the vaccine; those aged 5 to 11 receive one-third that the adult dose. The company is testing smaller sheep in babies aged six months to 19 months and kids 2 come 4 years of age; it expects those outcomes either later on this year or early on in 2022.

Moderna’s vaccine has actually been cleared for usage in civilization 18 and also older, though the company has it is registered an application to have the vaccine’s emergency authorization expanded to youths down to the age of 12. Top top Oct. 29, the FDA educated Moderna the it would certainly need much more time to examine that application, offered concerns around the higher rate of myocarditis in Moderna recipients. The agency said the decision could not come until January 2022. In light of the FDA’s announcement, Moderna shown it would delay applying because that an extension of that EUA come include children aged 6 to 11, till the decision on 12- come 17-year-olds has been issued.

At this suggest J&J’s vaccine is just authorized for human being 18 and also older. It has recently started a phase 3 efficacy psychological in youths age 12 to 17, but is considerably behind that two competitors in obtaining into the pediatric market.

Vaccine efficacy

The Pfizer and Moderna vaccines displayed astonishing — and essentially identical — degrees of efficacy, at the very least in the beforehand stages after vaccination.

The Pfizer vaccine confirmed efficacy that 95% at preventing symptomatic Covid infection after 2 doses. The vaccine showed up to be an ext or less equally protective throughout age groups and also racial and also ethnic groups.

The Moderna vaccine to be 94.1% reliable at staying clear of symptomatic Covid-19 after ~ the second dose. The vaccine’s efficacy showed up to it is in slightly reduced in people 65 and also older, however during a presentation to the Food and also Drug Administration’s advisory committee in December, the firm explained the the numbers might have been influenced by the reality there were few cases in that age group in the trial. The vaccine showed up to be same effective across different ethnic and racial groups.

But comparing the efficacy that those vaccines come the efficacy that Johnson & Johnson’s is daunting because of differences in the design of the phase 3 clinical exam — essentially the trials were experimentation for various outcomes. Pfizer’s and also Moderna’s trials both experiment for any type of symptomatic Covid infection. Pfizer began counting cases from 7 days ~ receipt of the second dose of vaccine, while Moderna waited till day 14 to begin counting cases.

J&J, by contrast, seek to determine whether one dose of its vaccine protected versus moderate to severe Covid disease — characterized as a mix of a confident test and also at the very least one symptom such as shortness of breath, beginning from 14 or 28 job after the single shot. (The company accumulated data because that both.)

Because of the distinction in the trials, making direct comparisons is a little bit like to compare apples and also oranges. Additionally, Pfizer and Moderna’s vaccines were tested before the emergence of troubling brand-new variants.

The J&J vaccine was still being tested as soon as the variants were making the rounds. Much of the data generated in the south African eight of the J&J trial involved people who were infected with the variant first seen in south Africa, dubbed Beta.


The J&J one-dose vaccine was presented to be 66% protective against moderate to major Covid infections overall from 28 work after injection, despite there to be variability based upon geographic locations. The vaccine was 72% safety in the joined States, 66% protective in south America, and 57% protective in south Africa.

But the vaccine was presented to it is in 85% protective against severe disease, v no differences throughout the eight countries or three areas in the study, nor throughout age groups amongst trial participants. And there were no hospitalizations or deaths in the vaccine arm of the trial after ~ the 28-day duration in which immunity developed.

The vaccines all appear to have actually lost some efficacy versus infection v the Delta variant, which became dominant in the United claims in summer 2021 — despite it’s not clear how much of the efficacy decline is because of the mutations the Delta or waning immunity as the months due to the fact that initial vaccination accumulate.

It likewise appears that, while the vaccines are preventing many infections, vaccinated world who have actually breakthrough infections v the Delta variant have the right to transmit the virus to rather (though they room not as contagious as unvaccinated people). Still, even with Delta, studies show that the vaccines have maintained their protectiveness against severe disease and death.

Number the doses/amounts the vaccine every dose

The primary series of both the Moderna and also the Pfizer vaccines is 2 shots: a priming dose, complied with by a booster shot. The interval in between Moderna sheep is 28 days; because that the Pfizer vaccine, the 21 days.

Each sheep of Pfizer’s consists of 30 micrograms of vaccine. Moderna went with a much bigger dose of vaccine, 100 micrograms. It way the agency is making use of a little much more than three times as much vaccine per person as Pfizer is. If Moderna’s initial outcomes didn’t it seems to be ~ to justify the much bigger dose, data suggest the defense the that company vaccine generates is decreasing at a slower rate than Pfizer’s is; part experts believe the higher dose might be at the very least partially responsible.

The J&J vaccine is, together mentioned, a single-dose vaccine. The firm has additionally tested a two-dose regimen, with the two shots offered 57 days apart. The outcomes from that 30,000-person trial were presented throughout an Oct. 15 meeting of FDA’s Vaccines and Related organic Products Advisory Committee, as component of its application for an EUA for its booster dose. (More top top this later.)

Durability the protection

Concerns around waning immunity space driving a variety of countries to sell their citizens booster shots, despite the reality that the director-general that the human being Health Organization, Tedros Adhanom Ghebreyesus, called for a moratorium on offering vaccine boosters till 2022 in stimulate to speed up very first doses of vaccine to low-income countries.

What appears to be happening is that as much more time passes after vaccination, protection versus all Covid infections starts come decline. Breakthrough situations — i m sorry are greatly mild — have started come increase. The decrease has been many pronounced among Pfizer recipients. Data indigenous the large health mechanism Kaiser Permanente of southerly California says the waning is many pronounced against the Delta different — the main household of SARS-CoV-2 viruses turn in the U.S. — yet even versus other variants protection has declined.


All three vaccines continue to offer solid protection against severe illness, though there is concern within the Biden administration that this as well will threaten if boosters space not given.

A key question at this suggest is whether the booster shots will certainly solidify defense in a means that is an ext sustained, or if these added doses mark the start of a consistent booster shot effort.

Booster status

For the functions of this discussion, there room two sorts of boosters.

The first is boosters or third shots for people who room moderately to severely immunocompromised — due to the fact that they are undergoing chemotherapy for cancer, since they have had an body organ transplant and also are ~ above immunosuppressive therapy, or due to the fact that they have advanced or untreated HIV. These to be authorized in respectable by the FDA because that the Pfizer-BioNTech and also Moderna vaccines, because of farming evidence that immunocompromised world might no be protected by the typical vaccine regimen.

The policy did not use to the one-dose J&J vaccine. That is unlikely countless immunocompromised human being would have actually opted because that this vaccine.

The second form of booster is designed to height up security from the early stage shot, in the instance of J&J, or series of shots, in the instances of Pfizer and also Moderna. All three companies have received authorizations for booster shots from the FDA.

Pfizer was the first to record with the agency, and also its booster was authorized in so late September for people 65 and also older, world 18 come 64 with medical conditions that progressive their hazard of serious Covid, and also people aged 18 to 64 whose jobs or life arrangements placed them at greater risk of significant Covid.

On Oct. 20, the FDA authorize EUAs for Moderna and also J&J’s boosters — and in the process, produced a an extremely interesting situation. (More on this in the next section.)

Unique among the companies, Moderna’s 3rd shot contains half as much antigen as its an initial two. (This is no the situation for world who space immunocompromised. Their 3rd dose that Moderna is a complete dose.) The emergency authorization claims that the Moderna booster have the right to be provided to the same groups of civilization as the Pfizer booster.


The FDA’s statement also presages that the boosters will quickly be made available to more people. Peter Marks, director of FDA’s facility for Biologics Evaluation and Research, has actually been publicly signaling the agency’s desire to reduced the period for booster doses for all — v no restrictions related come medical conditions or employment sector — to 40 native 65. And it has been reported that Pfizer will apply to the FDA to extend the authorization because that its booster come all adult 18 and older.

Both the Pfizer and Moderna boosters are available to civilization six month or later after the second dose in the series.

Not so v the J&J booster. The agency had want the booster to be provided six months or an ext after the early stage shot, other than in rare circumstances. However FDA’s vaccine advisers rejected that idea, express concern around the level the protection world get from the solitary shot. Lock recommended the everyone who got the J&J vaccine have to be vaccinated two months ~ the first dose — with a catchup period for world who are currently further the end from their very first shot.

Mix and also match boosters

It shows up getting a booster shot is going to it is in a “choose your own adventure” type of endure after the FDA stipulated that people eligible because that boosters have the right to choose any kind of of the jabs, nevertheless of what brand they at first received.

There is a farming body of evidence that an enhancing with a various vaccine might induce a more comprehensive and longer-lasting immune response — though some combinations may work better than others.

In announcing the emergency authorizations because that the Moderna and J&J boosters, the FDA stated no choice for that gets what, or in what order. Human being who gained J&J can gain a second shot that Moderna (the half dose) or Pfizer. Civilization who gained one of the mRNA vaccines can gain the J&J vaccine as their booster, the agency said.

Not stated in the FDA’s notice is the reality that this brand-new policy will make life much easier for folks moving booster shots, especially those trying to boost people living in permanent care, homeless shelters or prisons. They will require to lug only one vaccine when they walk to carry out booster shots, fairly than trying to match world to their initial vaccination brand.

Side-effect profile

In the vernacular the vaccinology, shots that cause a range of transient side results in a the majority of recipients are well-known as reactogenic.

All of these vaccines — in fact, most if no all the Covid-19 vaccines that have actually reported data so much — fall into the reactogenic category. The Advisory Committee ~ above Immunization Practices, the CDC’s experienced panel top top vaccines, advised hospitals at an early stage in the rollout the they can want to stagger vaccinations amongst employees in situation some feel also unwell to job-related the day after gift vaccinated.

The most typical side effects are injection site pain, fatigue, headache, muscle pain, and also joint pain. Some people in the clinical trials have actually reported fever. Through the Pfizer and also Moderna vaccines, side effects are an ext common ~ the second dose. Younger adults, that have much more robust immune systems, reported more side effects than enlarge adults.

To it is in clear: these side results are a authorize of an immune system kicking into gear. They carry out not signal the the vaccine is unsafe. To date there room no serious, long-term side effects connected with receipt of this vaccines, which will certainly be carefully monitored as their usage expands.


There have been reports of severe allergic reactions to the mRNA vaccines. Both the Pfizer and Moderna vaccines appear, on rare occasions, to trigger anaphylaxis, a severe and also potentially life-threatening reaction. World who build anaphylaxis must be treated v epinephrine — the medicine in EpiPens — and may have to be hospitalized come ensure their airways continue to be open. The CDC says world should it is in monitored for 15 minute after gaining a Covid-19 shot, and 30 minute if they have a background of significant allergies. J&J recently revealed that a solitary case that anaphylaxis has been report in someone who got its vaccine.

It will certainly take time come come up through a firm calculation of how frequently this side impact occurs. The many recent data from the CDC indicate that anaphylaxis occurs at a price of about 2.5 situations per one million doses provided of the Moderna vaccine, and 4.7 instances per million doses of the Pfizer. Many of the world who have occurred anaphylaxis have a history of significant allergies and some have had previous illustration of anaphylaxis.

The mRNA vaccines lug a little risk of myocarditis and also pericarditis, two species of love inflammation that space most generally seen soon after people receive their second shots, wellness officials have actually said. Guys under 40 seem to it is in at highest possible risk, specifically those aged 12 to 17. Most cases reported have actually been mild and also resolved.

The J&J also appears to have actually a serious — thought different — problem. A small number of individuals who obtained the vaccine have actually gone ~ above to develop thrombotic occasions in the week or 2 after vaccination; one has actually died. The thrombotic events encompass diffuse clots and low platelet levels, an unusual mix that have the right to be dangerous if treated improperly. The normal therapy for coagulation — a blood thinner referred to as heparin — would make the problem worse, the FDA said, warning doctors to ask for a Covid-19 vaccination history if they watch patients through that construction of symptoms.

Safety for those who room pregnant, lactating, or plan a pregnancy

Early on in the Covid vaccine rollout, there to be no data on which to determine if the vaccines were for sure for people who are pregnant or lactating. But after numerous studies, professionals have finish the vaccines room safe during pregnancy and lactationand furthermore, they are essential for these two groups to receive. This examine in the brand-new England newspaper of Medicine, for instance, looked in ~ the security of Pfizer and also Moderna vaccines in pregnant and also lactating people.

The CDC and the American college of Obstetricians and also Gynecologists recommend that people who are pregnant or lactating should get vaccinated, because of the threat Covid epidemic poses to them.

There are a the majority of rumors making the rounds that acquiring vaccinated against Covid will negatively impact a person’s capacity to conceive a child. ESPN football reporter Allison Williams recently announced she was quitting the network — which has a vaccine mandate — since she desires to have one more child.

There is no evidence that getting vaccinated versus Covid endangers fertility. In fact, a study released last month compared pregnancy rates amongst patients undergoing in vitro fertilization, feather to see if there to be differences among people who had actually been vaccinated, who had actually Covid antitoxin from infection, or had actually neither. “The present study failed to recognize the distinction in the implantation or pregnancy rates between women with documented seropositivity come the spike protein and women without seropositivity,” the authors reported.

Storage requirements

The mRNA vaccines require an elaborate cold chain, the term provided to explain the problems under i beg your pardon vaccines need to be stored throughout distribution and when they room in the doctors’ offices, pharmacies, or public wellness clinics whereby they’ll be administered.

The J&J shot walk not, which means this vaccine have the right to be given easily anywhere — in doctors’ offices, pharmacies, mass inoculation sites, public health clinics — as soon as supplies room adequate. It can be stored because that at the very least three months at the temperature that a continual refrigerator.

Of the mRNA vaccines, Pfizer’s was initially the more daunting to use. It had to be shipped and also stored in ultra-cold freezers — people that could keep the vials in ~ -94 levels Fahrenheit. Yet recently, the FDA announced the the vaccine can be shipped and also stored — because that one month just — at temperature of regular pharmacy freezers, in between -13 and also 5 levels Fahrenheit. That should make the last stage of the vaccine’s journey from manufacturing plant to syringe ready to plunge right into an arm somewhat easier.


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And Pfizer’s pediatric vaccine will certainly be easier still to administer, which might make it an ext likely pediatricians will become affiliated in the vaccine rollout. The 10-dose pediatric vaccine vial have the right to be save for approximately 10 weeks at refrigerator temperatures. The border of trust in between pediatricians and parents will certainly be vital in getting world who room uncertain about whether they desire to vaccinate their children to agree to do so.

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Moderna’s vaccine must be shipped at -4 levels Fahrenheit, i beg your pardon is within the range of a constant refrigerator freezer. The Moderna product is steady at fridge temperature because that 30 days and at room temperature because that 12 hours. J&J’s vaccine can be stored in ~ room temperature — no to exceed 77 levels Fahrenheit — because that 12 hrs when the vial hasn’t yet been punctured. After ~ the first dose is withdrawn, the vial can be stored in a refrigerator for six hrs or at room temperature for 2 hours.

Andrew Joseph contributed reporting. 

An previously version that this story mischaracterized the way in which famous vectored vaccines work and incorrectly declared that the single dose J&J vaccine contains much more antigen 보다 the doses in the two-dose regimen.