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Latest on Omicron Variant and COVID-19 Vaccine Protection

Posted on by Dr. Francis Collins

Graph. People with two shots and booster. 25 times more protection from Omicron
Credit: Adapted from Pfizer, Dec. 8, 2021

There’s been great concern about the new Omicron variant of SARS-CoV-2, the coronavirus that causes COVID-19. A major reason is Omicron has accumulated over 50 mutations, including about 30 in the spike protein, the part of the coronavirus that mRNA vaccines teach our immune systems to attack. All of these genetic changes raise the possibility that Omicron could cause breakthrough infections in people who’ve already received a Pfizer or Moderna mRNA vaccine.

So, what does the science show? The first data to emerge present somewhat encouraging results. While our existing mRNA vaccines still offer some protection against Omicron, there appears to be a significant decline in neutralizing antibodies against this variant in people who have received two shots of an mRNA vaccine.

However, initial results of studies conducted both in the lab and in the real world show that people who get a booster shot, or third dose of vaccine, may be better protected. Though these data are preliminary, they suggest that getting a booster will help protect people already vaccinated from breakthrough or possible severe infections with Omicron during the winter months.

Though Omicron was discovered in South Africa only last month, researchers have been working around the clock to learn more about this variant. Last week brought the first wave of scientific data on Omicron, including interesting work from a research team led by Alex Sigal, Africa Health Research Institute, Durban, South Africa [1].

In lab studies working with live Omicron virus, the researchers showed that this variant still relies on the ACE2 receptor to infect human lung cells. That’s really good news. It means that the therapeutic tools already developed, including vaccines, should generally remain useful for combatting this new variant.

Sigal and colleagues also tested the ability of antibodies in the plasma from 12 fully vaccinated individuals to neutralize Omicron. Six of the individuals had no history of COVID-19. The other six had been infected with the original variant in the first wave of infections in South Africa.

As expected, the samples showed very strong neutralization against the original SARS-CoV-2 variant. However, antibodies from people who’d been previously vaccinated with the two-dose Pfizer vaccine took a significant hit against Omicron, showing about a 40-fold decline in neutralizing ability.

This escape from immunity wasn’t complete. Indeed, blood samples from five individuals showed relatively good antibody levels against Omicron. All five had previously been infected with SARS-CoV-2 in addition to being vaccinated. These findings add to evidence on the value of full vaccination for protecting against reinfections in people who’ve had COVID-19 previously.

Also of great interest were the first results of the Pfizer study, which the company made available in a news release [2]. Pfizer researchers also conducted laboratory studies to test the neutralizing ability of blood samples from 19 individuals one month after a second shot compared to 20 others one month after a booster shot.

These studies showed that the neutralizing ability of samples from those who’d received two shots had a more than 25-fold decline relative to the original virus. Together with the South Africa data, it suggests that the two-dose series may not be enough to protect against breakthrough infections with the Omicron variant.

In much more encouraging news, their studies went on to show that a booster dose of the Pfizer vaccine raised antibody levels against Omicron to a level comparable to the two-dose regimen against the original variant (as shown in the figure above). While efforts already are underway to develop an Omicron-specific COVID-19 vaccine, these findings suggest that it’s already possible to get good protection against this new variant by getting a booster shot.

Very recently, real-world data from the United Kingdom, where Omicron cases are rising rapidly, are providing additional evidence for how boosters can help. In a preprint [3], Andrews et. al showed the effectiveness of two shots of Pfizer mRNA vaccine trended down after four months to about 40 percent. That’s not great, but note that 40 percent is far better than zero. So, clearly there is some protection provided.

Graph showing Pfizer booster is about 80% effective after 2 weeks against Omicron
Credit: Andrews N, et al., 2021

Most impressively (as shown in the figure from Andrews N, et al.) a booster substantially raised that vaccine effectiveness to about 80 percent. That’s not quite as high as for Delta, but certainly an encouraging result. Once again, these data show that boosting the immune system after a pause produces enhanced immunity against new viral variants, even though the booster was designed from the original virus. Your immune system is awfully clever. You get both quantitative and qualitative benefits.

It’s also worth noting that the Omicron variant mostly doesn’t have mutations in portions of its genome that are the targets of other aspects of vaccine-induced immunity, including T cells. These cells are part of the body’s second line of defense and are generally harder for viruses to escape. While T cells can’t prevent infection, they help protect against more severe illness and death.

It’s important to note that scientists around the world are also closely monitoring Omicron’s severity While this variant appears to be highly transmissible, and it is still early for rigorous conclusions, the initial research indicates this variant may actually produce milder illness than Delta, which is currently the dominant strain in the United States.

But there’s still a tremendous amount of research to be done that could change how we view Omicron. This research will take time and patience.

What won’t change, though, is that vaccines are the best way to protect yourself and others against COVID-19. (And these recent data provide an even-stronger reason to get a booster now if you are eligible.) Wearing a mask, especially in public indoor settings, offers good protection against the spread of all SARS-CoV-2 variants. If you’ve got symptoms or think you may have been exposed, get tested and stay home if you get a positive result. As we await more answers, it’s as important as ever to use all the tools available to keep yourself, your loved ones, and your community happy and healthy this holiday season.


[1] SARS-CoV-2 Omicron has extensive but incomplete escape of Pfizer BNT162b2 elicited neutralization and requires ACE2 for infection. Sandile C, et al. Sandile C, et al. medRxiv preprint. December 9, 2021.

[2] Pfizer and BioNTech provide update on Omicron variant. Pfizer. December 8, 2021.

[3] Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern. Andrews N, et al. preprint. December 10, 2021.


COVID-19 Research (NIH)

Sigal Lab (Africa Health Research Institute, Durban, South Africa)


  • Antonio Talluri says:

    “Credit: Adapted from Pfizer, Dec. 8, 2021″….it’s a bit odd to use directly the claims of the vaccine manufacturer. Peer review is out of fashion? We ( western subjects all over the Word) are all starving and eager to read unbiased information. Our faith is diluting, weekly.

    • Michael Apostolides says:

      There is no time for peer review. These studies were just posted and peer review takes time

    • Todd Shilt says:

      Yes I agree. Furthermore, the director is giving advice that worsens this pandemic. Way too much faith in masks. In America 99% wear cloth masks. AND if you think you were exposed dont wait to quarantine after test results…. stay home til you get the negative.

      • Copeland says:

        You are exposed all the time if you are in the public. Do you mean quarantine after a potentially positive test result? And what about treatment. Where in this blog is front end treatment of Sars-cov-2 being talked about? Seek medical attention, get early treatments available? Masks are not treatment and nothing to do with a booster.

  • T Kwan says:

    Were there any research results on the effectiveness with two doses of Moderna and the decrease in neutralizing titers after 6-9 months and level after booster? I know boosters help, but if this is a global problem why are boosters more important than getting the world vaccinated. Otherwise, there will be endless boosters every six months or worse more often for each worse variant.

  • Maria Rosa Bono says:

    I am an immunologist working at the University of Chile, and due to the pandemic, I have become involved in COVID-19. I want to ask you if you have read a recent paper from a group in Israel … showing results about the third dose with Pfizer in Israel that had a Delta variant flare-up. I found in Fig. 4c an interesting result showing that deceased people decreased when they started using an especially Pfizer booster produced against the Delta variant and used as of July 30, 2021, in people aged 60+. Although this trial does not have the control of having used the original Pfizer vaccine as a booster, probably for ethical reasons, the result is extraordinary. Why is this unique booster not being used in Europe, which continues to have a considerable increase in infected and deceased people today? I believe that several other experiences can be taken out of the “real world” by looking, for example, at what is happening in South America.

    • Bob says:

      Please provide citation for the Israeli study you refer to

    • ana cecilia says:

      what is happening in South America?

      • Maria Rosa Bono says:

        Ana, in Chile, we have passed the wave of the Delta variant, and there was hardly a slight increase in those infected and hospitalized. Delta entered Chile on June 24, 2021, and is currently the variant that circulates in more than 97% of infected individuals. In Chile, people got CoronaVac mainly, and after five months, people received a booster of Astrazeneka or Pfizer, and in a few cases, the third dose of CoronaVac vaccine. Our data show that CoronaVac, then a booster with another vaccine, induces a high amount of antibodies against the virus. There have been essential immunization programs in Chile, and children are now vaccinated from three years with CoronaVac. Therefore the inactivated virus vaccine maybe be more effective against the variants than the mRNA vaccines. Omicron has just arrived in Chile now, and we do not know how our vaccination scheme will work, but we will know it very soon.

    • P.E. says:

      Israel only gives Pfizer

  • Cristina Morganti-Kossmann says:

    It would be useful to know the effectiveness of other vaccines in protecting from the omicron variant. Most research revolves around the Pfizer but AZ for instance is more commonly used against COVID.

  • David Sinclair says:

    Are you referring to,half dose or full dose boosters?

  • JJ Sikora says:

    Once again the virus mutates and the rush to insure the public that just another injection of either of the 3 major vaccines currently in use, are the answer to the recurrence of the covid 19 infections. At the same time, they warn that more break through infections are possible and thus may require a 4th dose, inorder to mitigate the infections from spreading and or mutating further. Yet there are other vaccines waiting for FDA approval that may be more effective and which are still not getting approved or whose effectiveness/ capabilities are not being discussed. The new astrazenica antibody cocktail has a fact sheet who shows a very limited testing population and a very serious cardiac warning that wasn’t expected. The list of adverse effects did not include the warning of serious cardiac symptoms. That that antibody cocktail was so needed by those whose medical issues were a poor choice with the current 3 major vaccines. The there was a recall on the one antibody infusion which was used to help those infected to prevent death.

    It would be in the best interests of the public to review the vaccines that are new and whose efficacy may be more than others and whose side effects would be less dire to the health of the public, whose physiology requires a more careful adverse effect ratios.

  • Jean says:

    What about if you had the Pfzier vaccine and then a break through case of the Delta variant, what is the estimated protection against Omicron? I ended up with some issues after the vaccine and breakthrough covid and cardiologist recommended against booster since I had natural immunities from having Delta. But do I against this new Omicron variant?

    • Kathie says:

      Unless you get tested then you don’t know how long that immunity will last. I have a friend that got covid with no symptoms and three months later she got it again and died.

    • Paul Borger says:

      I have the same question Jean. I had an suspected autoimmune reaction to my first Pfizer (basically feels like long COVID) and have been advised against an mRNA vaccine.

  • peggi jeung says:

    This information leaves out all the people who received the J&J one shot vaccine and are looking for guidance. It’s like we don’t exist.

  • Frederick Salim Hannawi says:

    Is there anything wrong with allowing persons with strong immune response to just rely on their innate immune response systems to naturally deploy NK, NKT, T, Cells to kill “any” virus that they naturally come into contact with for the B cells to do their work and to allow the CD4+ – CD8+ T cell range to mop up and cleanup virus infected cells as opposed to deploying vaccine (1) that targets T cells to kill covid-19 virus (1) that misses out on variants that mutates whilst in the human host thereby leaving the mutant variants to remaining in the host in stealth mode totally unnoticed by current covid-19 (1) vaccines.

    Would a second, third or fourth dose of covid-19 vaccines not targeted to variants of viruses unknown to the current covid-19 vaccine really discover those new variants already in the body in stealth mode?

    • Carol N. says:

      What about those of us who initially received a J&J vaccine followed by a Pfizer boost? Are we protected or do we need another boost? When are we going to know the efficacy of the mix and match? The government told everyone to get the first vaccine available and we did. Unfortunately, it was J&J. Now we are the forgotten. Moderna and Pfizer are all we hear about. We feel like sitting ducks out here.

  • Zuccheri Gianni says:

    The Covid, the family and … the dog?

    I heard that a family of friends fell ill with Covid, fortunately in a moderate form: will it be useful to evaluate whether their dog is also involved?
    In case it is infected and not recognized, what role could the pet play in the evolution of the variants of SARS-CoV-2?

    Several articles evaluate the possibility (although infrequent) that pets are also infected with SARS-CoV-2, an example:

    Transbound Emerg Dis
    . 2021 Nov 1;10.1111/tbed.14366.
    Large-scale study on virological and serological prevalence of SARS-CoV-2 in cats and dogs in Spain

  • Jamie says:

    If you are totally unvaccinated to all strains and catch omicron can it give you any natural immunity against the Delta strain? If so How effective would that be?

  • Fahmida P says:

    what about the all other vaccines?

  • Orin Buck says:

    Is there any information available about Omicron infectiousness such as how long before one person infects another in a closed room, how long before 2 masked people infect each other, what types of masks don’t protect against Omicron, what is the new safe social distance—isn’t it much bigger, since you say Omicron is incredibly infectious?

  • Greta J. says:

    Thanks for the updated information about how the COVID vaccine stops the omicron variant. I think it is time for myself and my children to get a COVID vaccine. I don’t want to wait in a long line, so I will be sure to find a medical center that takes appointments so we can get our vaccines done quickly.

  • J.Fine says:

    I have worn an N95 Mask and Nitrile Gloves since March of 2020. I eventually changed to an N99 then to an N99.97 mask. I wore it in stores at work and at gas stations. I waited patiently for news of a vaccine, trying to never let my guard down. On TV and On the Internet Since January 2020 I saw that in China EVERYBODY was wearing a mask. You could not see a single Chinese person NOT wearing a mask. At the same time in the US we were told by our Government officials “We did not need to wear masks.” That was the worst advice any government could give to its people. I reasoned that since this was a corona virus (aka “common cold”) that it was a respiratory virus spread through human contact, first in the sinus cavities then in the oral cavity and eventually in the lungs. Anything one could do to limit the amount of Viral Load (the amount of virus particles one is exposed to on a daily basis) would be of benefit to one. The disaster was that while other countries encouraged their people to wear masks the US was a “fools paradise” of people ignoring the lesson that China had learned. Add to that . . . people believing that microchips can fit in a hypodermic syringe. Microchips are indeed small but they are NOT that small to fit in an injectable “needle.” . . . Masks do help a lot. Germs and viruses exploit the social activity of human beings. Animals can also be infected with corona viruses as well.

  • Steve says:

    If a person is exposed to another with Covid, gets PCR or antigen tests, positive but minimal symptoms. Wants monoclonal antibody injections. How does that person know if the virus is Delta or Omicron? Regeneron apparently very weak against Omicron, but other MCA’s are stronger. Question is how do you know which variant you have?

  • Ankur V. says:

    If a person was infected of COVID and completed her/his vaccination course, then does she/he need to go for booster shot?

  • Judith H Hartley says:

    People in China have been wearing masks for a long time because they have a ton of pollution, they cook and eat animals right off the street, they have unsanitary ways of doing some things. Masks do help with illnesses, people in the US seem to not believe what is happening, blows my mind.

  • C.B. says:

    Thank you very much for your information. People who are looking for protection against Corona, your information is very helpful.

  • A.D. says:

    Wow this is an amazing, a great blog I ever read …

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