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Dr. Francis Collins

Accelerating COVID-19 Vaccine Testing with ‘Correlates of Protection’

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Women walking with two insets showing 1. Few antibodies labeled "Vaccine efficacy of 78%" and 2, many antibodies labeled, "Vaccine efficacy of 98%

With Omicron now on so many people’s minds, public health officials and virologists around the world are laser focused on tracking the spread of this concerning SARS-CoV-2 variant and using every possible means to determine the effectiveness of our COVID-19 vaccines against it. Ultimately, the answer will depend on what happens in the real world. But it will also help to have a ready laboratory means for gauging how well a vaccine works, without having to wait many months for the results in the field.

With this latter idea in mind, I’m happy to share results of an NIH-funded effort to understand the immune responses associated with vaccine-acquired protection against SARS-CoV-2 [1]. The findings, based on the analysis of blood samples from more than 1,000 people who received the Moderna mRNA vaccine, show that antibody levels do correlate, albeit somewhat imperfectly, with how well a vaccine works to prevent infection.

Such measures of immunity, known as “correlates of protection,” have potential to support the approval of new or updated vaccines more rapidly. They’re also useful to show how well a vaccine will work in groups that weren’t represented in a vaccine’s initial testing, such as children, pregnant women, and those with certain health conditions.

The latest study, published in the journal Science, comes from a team of researchers led by Peter Gilbert, Fred Hutchinson Cancer Research Center, Seattle; David Montefiori, Duke University, Durham, NC; and Adrian McDermott, NIH’s Vaccine Research Center, National Institute of Allergy and Infectious Diseases.

The team started with existing data from the Coronavirus Efficacy (COVE) trial. This phase 3 study, conducted in 30,000 U.S. adults, found the Moderna vaccine was safe and about 94 percent effective in protecting people from symptomatic infection with SARS-CoV-2 [2].

The researchers wanted to understand the underlying immune responses that afforded that impressive level of COVID-19 protection. They also sought to develop a means to measure those responses in the lab and quickly show how well a vaccine works.

To learn more, Gilbert’s team conducted tests on blood samples from COVE participants at the time of their second vaccine dose and again four weeks later. Two of the tests measured concentrations of binding antibodies (bAbs) that latch onto spike proteins that adorn the coronavirus surface. Two others measured the concentration of more broadly protective neutralizing antibodies (nAbs), which block SARS-CoV-2 from infecting human cells via ACE2 receptors found on their surfaces.

Each of the four tests showed antibody levels that were consistently higher in vaccine recipients who did not develop COVID-19 than in those who did. That is consistent with expectations. But these data also allowed the researchers to identify the specific antibody levels associated with various levels of protection from disease.

For those with the highest antibody levels, the vaccine offered an estimated 98 percent protection. Those with levels about 1,000 times lower still were well protected, but their vaccine efficacy was reduced to about 78 percent.

Based on any of the antibodies tested, the estimated COVID-19 risk was about 10 times lower for vaccine recipients with antibodies in the top 10 percent of values compared to those with antibodies that weren’t detectable. Overall, the findings suggest that tests for antibody levels can be applied to make predictions about an mRNA vaccine’s efficacy and may be used to guide modifications to the current vaccine regimen.

To understand the significance of this finding, consider that for a two-dose vaccine like Moderna or Pfizer, a trial using such correlates of protection might generate sufficient data in as little as two months [3]. As a result, such a trial might show whether a vaccine was meeting its benchmarks in 3 to 5 months. By comparison, even a rapid clinical trial done the standard way would take at least seven months to complete. Importantly also, trials relying on such correlates of protection require many fewer participants.

Since all four tests performed equally well, the researchers say it’s conceivable that a single antibody assay might be sufficient to predict how effective a vaccine will be in a clinical trial. Of course, such trials would require subsequent real-world studies to verify that the predicted vaccine efficacy matches actual immune protection.

It should be noted that the Food and Drug Administration (FDA) would need to approve the use of such correlates of protection before their adoption in any vaccine trial. But, to date, the totality of evidence on neutralizing antibody responses as correlates of protection—for which this COVE trial data is a major contributor—is impressive.

Neutralizing antibody levels are also now being considered for use in future coronavirus vaccine trials. Indeed, for the EUA of Pfizer’s mRNA vaccine for 5-to-11-year-olds, the FDA accepted pre-specified success criteria based on neutralizing antibody responses in this age group being as good as those observed in 16- to 25-year-olds [4].

Antibody levels also have been taken into consideration for decisions about booster shots. However, it’s important to note that antibody levels are not precise enough to help in deciding whether or not any particular individual needs a COVID-19 booster. Those recommendations are based on how much time has passed since the original immunization.

Getting a booster is a really good idea heading into the holidays. The Delta variant remains very much the dominant strain in the U.S., and we need to slow its spread. Most experts think the vaccines and boosters will also provide some protection against the Omicron variant—though the evidence we need is still a week or two away. The Centers for Disease Control and Prevention (CDC) recommends a COVID-19 booster for everyone ages 18 and up at least six months after your second dose of mRNA vaccine or two months after receiving the single dose of the Johnson & Johnson vaccine [5]. You may choose to get the same vaccine or a different one. And, there is a place near you that is offering the shot.


[1] Immune correlates analysis of the mRNA-1273 COVID-19 vaccine efficacy clinical trial.
Gilbert PB, Montefiori DC, McDermott AB, Fong Y, Benkeser D, Deng W, Zhou H, Houchens CR, Martins K, Jayashankar L, Castellino F, Flach B, Lin BC, O’Connell S, McDanal C, Eaton A, Sarzotti-Kelsoe M, Lu Y, Yu C, Borate B, van der Laan LWP, Hejazi NS, Huynh C, Miller J, El Sahly HM, Baden LR, Baron M, De La Cruz L, Gay C, Kalams S, Kelley CF, Andrasik MP, Kublin JG, Corey L, Neuzil KM, Carpp LN, Pajon R, Follmann D, Donis RO, Koup RA; Immune Assays Team§; Moderna, Inc. Team§; Coronavirus Vaccine Prevention Network (CoVPN)/Coronavirus Efficacy (COVE) Team§; United States Government (USG)/CoVPN Biostatistics Team§. Science. 2021 Nov 23:eab3435.

[2] Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. Baden LR, El Sahly HM, Essink B, Kotloff K, Frey S, Novak R, Diemert D, Spector SA, Rouphael N, Creech CB, McGettigan J, Khetan S, Segall N, Solis J, Brosz A, Fierro C, Schwartz H, Neuzil K, Corey L, Gilbert P, Janes H, Follmann D, Marovich M, Mascola J, Polakowski L, Ledgerwood J, Graham BS, Bennett H, Pajon R, Knightly C, Leav B, Deng W, Zhou H, Han S, Ivarsson M, Miller J, Zaks T; COVE Study Group. N Engl J Med. 2021 Feb 4;384(5):403-416.

[3] A government-led effort to identify correlates of protection for COVID-19 vaccines. Koup RA, Donis RO, Gilbert PB, Li AW, Shah NA, Houchens CR. Nat Med. 2021 Sep;27(9):1493-1494.

[4] Evaluation of the BNT162b2 Covid-19 vaccine in children 5 to 11 years of age. Walter EB, Talaat KR, Sabharwal C, Gurtman A, Lockhart S, Paulsen GC, Barnett ED, Muñoz FM, Maldonado Y, Pahud BA, Domachowske JB, Simões EAF, Sarwar UN, Kitchin N, Cunliffe L, Rojo P, Kuchar E, Rämet M, Munjal I, Perez JL, Frenck RW Jr, Lagkadinou E, Swanson KA, Ma H, Xu X, Koury K, Mather S, Belanger TJ, Cooper D, Türeci Ö, Dormitzer PR, Şahin U, Jansen KU, Gruber WC; C4591007 Clinical Trial Group. N Engl J Med. 2021 Nov 9:NEJMoa2116298.

[5] COVID-19 vaccine booster shots. Centers for Disease Control and Prevention. Nov 29, 2021.


COVID-19 Research (NIH)

COVID-19 Prevention Network

Combat COVID (U.S. Department of Health and Human Services)

Peter Gilbert (Fred Hutchison Cancer Research Center)

David Montefiori (Duke University, Durham, NC)

Adrian McDermott (National Institute of Allergy and Infectious Diseases/NIH)

NIH Support: National Institute of Allergy and Infectious Diseases

Welcoming President Biden

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On December 2, President Joe Biden visited NIH for a briefing on the importance of vaccines and booster shots. They remain vital this holiday season to slowing the spread of the SARS-CoV-2 coronavirus, the cause of COVID-19, and saving lives. It was my honor to greet the President, though with a careful fist bump, and I got to speak with him briefly before he delivered his remarks about the White House’s strategy for fighting COVID-19 this winter. Credit: NIH

Tapping Into The Brain’s Primary Motor Cortex

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If you’re like me, you might catch yourself during the day in front of a computer screen mindlessly tapping your fingers. (I always check first to be sure my mute button is on!) But all that tapping isn’t as mindless as you might think.

While a research participant performs a simple motor task, tapping her fingers together, this video shows blood flow within the folds of her brain’s primary motor cortex (gray and white), which controls voluntary movement. Areas of high brain activity (yellow and red) emerge in the omega-shaped “hand-knob” region, the part of the brain controlling hand movement (right of center) and then further back within the primary somatic cortex (which borders the motor cortex toward the back of the head).

About 38 seconds in, the right half of the video screen illustrates that the finger tapping activates both superficial and deep layers of the primary motor cortex. In contrast, the sensation of a hand being brushed (a sensory task) mostly activates superficial layers, where the primary sensory cortex is located. This fits with what we know about the superficial and deep layers of the hand-knob region, since they are responsible for receiving sensory input and generating motor output to control finger movements, respectively [1].

The video showcases a new technology called zoomed 7T perfusion functional MRI (fMRI). It was an entry in the recent Show Us Your BRAINs! Photo and Video Contest, supported by NIH’s Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative.

The technology is under development by an NIH-funded team led by Danny J.J. Wang, University of Southern California Mark and Mary Stevens Neuroimaging and Informatics Institute, Los Angeles. Zoomed 7T perfusion fMRI was developed by Xingfeng Shao and brought to life by the group’s medical animator Jim Stanis.

Measuring brain activity using fMRI to track perfusion is not new. The brain needs a lot of oxygen, carried to it by arteries running throughout the head, to carry out its many complex functions. Given the importance of oxygen to the brain, you can think of perfusion levels, measured by fMRI, as a stand-in measure for neural activity.

There are two things that are new about zoomed 7T perfusion fMRI. For one, it uses the first ultrahigh magnetic field imaging scanner approved by the Food and Drug Administration. The technology also has high sensitivity for detecting blood flow changes in tiny arteries and capillaries throughout the many layers of the cortex [2].

Compared to previous MRI methods with weaker magnets, the new technique can measure blood flow on a fine-grained scale, enabling scientists to remove unwanted signals (“noise”) such as those from surface-level arteries and veins. Getting an accurate read-out of activity from region to region across cortical layers can help scientists understand human brain function in greater detail in health and disease.

Having shown that the technology works as expected during relatively mundane hand movements, Wang and his team are now developing the approach for fine-grained 3D mapping of brain activity throughout the many layers of the brain. This type of analysis, known as mesoscale mapping, is key to understanding dynamic activities of neural circuits that connect brain cells across cortical layers and among brain regions.

Decoding circuits, and ultimately rewiring them, is a major goal of NIH’s BRAIN Initiative. Zoomed 7T perfusion fMRI gives us a window into 4D biology, which is the ability to watch 3D objects over time scales in which life happens, whether it’s playing an elaborate drum roll or just tapping your fingers.


[1] Neuroanatomical localization of the ‘precentral knob’ with computed tomography imaging. Park MC, Goldman MA, Park MJ, Friehs GM. Stereotact Funct Neurosurg. 2007;85(4):158-61.

[2]. Laminar perfusion imaging with zoomed arterial spin labeling at 7 Tesla. Shao X, Guo F, Shou Q, Wang K, Jann K, Yan L, Toga AW, Zhang P, Wang D.J.J bioRxiv 2021.04.13.439689.


Brain Basics: Know Your Brain (National Institute of Neurological Disorders and Stroke)

Laboratory of Functional MRI Technology (University of Southern California Mark and Mary Stevens Neuroimaging and Informatics Institute)

The Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative (NIH)

Show Us Your BRAINs! Photo and Video Contest (BRAIN Initiative)

NIH Support: National Institute of Neurological Disorders and Stroke; National Institute of Biomedical Imaging and Bioengineering; Office of the Director

Encouraging News on Gene Therapy for Hemophilia A

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Factor VIII gene carried in AAV Vector plus Immunosuppressive drugs; person with hemophilia A; microscopic view of blood with Factor VIII

About 20,000 people in the U.S. live with hemophilia A. It’s a rare X-linked genetic disorder that affects predominantly males and causes their blood to clot poorly when healing wounds. For some, routine daily activities can turn into painful medical emergencies to stop internal bleeding, all because of changes in a single gene that disables an essential clotting protein.

Now, results of an early-stage clinical trial, published recently in the New England Journal of Medicine, demonstrate that gene therapy is within reach to produce the essential clotting factor in people with hemophilia A. The results show that, in most of the 18 adult participants, a refined gene therapy strategy produced lasting expression of factor VIII (FVIII), the missing clotting factor in hemophilia A [1]. In fact, gene therapy helped most participants reduce—or, in some cases, completely eliminate—bleeding events.

Currently, the most-common treatment option for males with hemophilia A is intravenous infusion of FVIII concentrate. Though infused FVIII becomes immediately available in the bloodstream, these treatments aren’t a cure and must be repeated, often weekly or every other day, to prevent or control bleeding.

Gene therapy, however, represents a possible cure for hemophilia A. Earlier clinical trials reported some success using benign adeno-associated viruses (AAVs) as the vector to deliver the therapeutic FVIII gene to cells in the liver, where the clotting protein is made. But after a year, those trial participants had a marked decline in FVIII expression. Follow-up studies then found that the decline continued over time, thought to be at least in part because of an immune response to the AAV vector.

In the new study, an NIH-funded team led by Lindsey George and Katherine High of the Children’s Hospital of Philadelphia and the University of Pennsylvania, tested their refined delivery system. High is also currently with Asklepios BioPharmaceutical, Inc., Chapel Hill, NC. (Back in the 1970s, she and I were medical students in the same class at the University of North Carolina.) The study was also supported by Spark Therapeutics, Philadelphia.

Trial participants received a single infusion of the novel recombinant AAV-based gene therapy called SPK-8011. It is specifically designed to produce FVIII expression in the liver. In this phase 1/2 clinical trial, which evaluates the safety and initial efficacy of a treatment, participants received one of four different doses of SPK-8011. Most also received steroids to prevent or treat the presumed counterproductive immune response to the therapy.

The researchers followed participants for a year after the experimental treatment, and all enrolled in a follow-up trial for continued observation. During this time, researchers detected no major safety concerns, though several patients had increases in blood levels of a liver enzyme.

The great news is all participants produced the missing FVIII after gene therapy. Twelve of the 16 participants were followed for more than two years and had no apparent decrease in clotting factor activity. This is especially noteworthy because it offers the first demonstration of multiyear stable and durable FVIII expression in individuals with hemophilia A following gene transfer.

Even more encouraging, the men in the trial had more than a 92 percent reduction in bleeding episodes on average. Before treatment, most of the men had 8.5 bleeding episodes per year. After treatment, those events dropped to an average of less than one per year. However, two study participants lost FVIII expression within a year of treatment, presumably due to an immune response to the therapeutic AAV. This finding shows that, while steroids help, they don’t always prevent loss of a therapeutic gene’s expression.

Overall, the findings suggest that AAV-based gene therapy can lead to the durable production of FVIII over several years and significantly reduce bleeding events. The researchers are now exploring possibly more effective ways to control the immune response to AAV in expansion of this phase 1/2 investigation before pursuing a larger phase 3 trial. They’re continuing to monitor participants closely to establish safety and efficacy in the months and years to come.

On a related note, the recently announced Bespoke Gene Therapy Consortium (BGTC), a partnership between NIH and industry, will expand the refined gene therapy approach demonstrated here to more rare and ultrarare diseases. That should make these latest findings extremely encouraging news for the millions of people born with other rare genetic conditions caused by known alterations to a single gene.


[1] Multiyear Factor VIII expression after AAV Gene transfer for Hemophilia A. George LA, Monahan PE, Eyster ME, Sullivan SK, Ragni MV, Croteau SE, Rasko JEJ, Recht M, Samelson-Jones BJ, MacDougall A, Jaworski K, Noble R, Curran M, Kuranda K, Mingozzi F, Chang T, Reape KZ, Anguela XM, High KA. N Engl J Med. 2021 Nov 18;385(21):1961-1973.


Hemophilia A (National Center for Advancing Translational Sciences/NIH)

FAQ About Rare Diseases (National Center for Advancing Translational Sciences/NIH)

Bespoke Gene Therapy Consortium (BGTC) (NIH)

Accelerating Medicines Partnership® (AMP®) (NIH)

Lindsey George (University of Pennsylvania, Philadelphia)

Katherine High (University of Pennsylvania)

NIH Support: National Heart, Lung, and Blood Institute

A Special Thanksgiving Day Concert

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What an inspiring afternoon I spent at the NIH Clinical Center. Caesar Sant, a 13-year-old violinist and child prodigy whose family now lives in the Memphis area, gave a special Thanksgiving Day concert. I got to accompany on guitar, but the moment belonged to his amazing talent. Caesar was born in August 2008 with sickle cell disease. As a participant in an NIH clinical trial, Caesar recently received a bone marrow transplant in hopes of curing his disease. So far so good.

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