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Why it takes 2 shots to make mRNA vaccines do their antibody-creating best – and what the data shows on delaying the booster dose

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Professor of Medicine, University of Virginia
William Petri receives research funding from the NIH, the Bill & Melinda Gates Foundation and Regeneron, Inc.

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With the U.S. facing vaccination delays because of worker shortages and distribution problems, federal health officials now say it’s OK to push back the second dose of the two-part vaccine by as much as six weeks.
As an infectious disease doctor, I’ve been fielding a lot of questions from my patients as well as my friends and family about whether the COVID-19 vaccine will still work if people are late receiving their second dose.
Two doses, separated by three to four weeks, is the tried-and-true approach to generate an effective immune response through vaccination, not just for COVID but for hepatitis A and B and other diseases as well.
The first dose primes the immune system and introduces the body to the germ of interest. This allows the immune system to prepare its defense. The second dose, or booster, provides the opportunity for the immune system to ramp up the quality and quantity of the antibodies used to fight the virus.
In the case of the Pfizer and Moderna COVID-19 vaccines, the second dose increases the protection afforded by the vaccine from 60% to approximately 95%.
In the clinical trial, the second dose of the Pfizer vaccine was administered as early as day 19 and as late as day 42 to 93% of the subjects. Since protection was approximately 95% for everyone who was vaccinated within this time “window,” there is little reason not to allow some flexibility in the timing of the second dose 2.
As more vaccine becomes available, the timing of the second dose should be close to four weeks for the Pfizer and Moderna vaccines. But the good news is that even while supplies remain limited, the science suggests that there’s nothing bad about getting a second dose as late as 42 days after the first.
The biology through which the mRNA vaccines induce their protection from COVID-19 is fundamentally different from that with other vaccines.
Pfizer and Moderna vaccines use messenger RNA that encodes the spike glycoprotein. Upon injection of the vaccine, the mRNA enters into immune cells called dendritic cells. The dendritic cells use the instructions written in the mRNA to synthesize the hallmark spike glycoprotein, which characterizes the SARS-CoV-2 virus that causes COVID-19. These immune cells then show the spike glycoprotein to B-cells, which then make anti-spike antibodies.
The mRNA vaccines are uniquely capable of inducing a special kind of immune cell – called a T-follicular helper cell – to help B-cells produce antibodies. The T-cells do this through direct contact with the B-cells and by sending chemical signals that tell the B-cells to produce antibodies. It is this help in antibody production that makes these vaccines so effective.
But not all B-cells are the same. There are two kinds that make anti-spike antibodies: long-lived plasma cells and memory B-cells. The long-lived plasma cells, as their name implies, live in the bone marrow for years after vaccination, continuously churning out antibody – in this case anti-spike antibody. These long-lived B-cells do not need to be boosted.
The memory B-cells, on the other hand, live in a state akin to hibernation. They do not produce antibodies until stimulated by a booster of the vaccine, or are exposed to infection with the coronavirus that causes COVID-19. That is the reason we need that second dose. Together these two types of B-cells provide a constant level of protection.
With current vaccine shortages, and problems with setting up the infrastructure to vaccinate millions of people, many physicians are concerned that the second dose of vaccine won’t be delivered in the prescribed three-to-four-week window.
That booster shot is necessary for the T-cells to stimulate the memory B-cells to produce massive quantities of antibodies. If the booster isn’t given within the appropriate window, lower quantities of antibodies will be produced that may not provide as powerful protection from the virus.
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We’re building a vaccine corps of medical and nursing students – they could transform how we reach underserved areas

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Chancellor and Professor of Population & Quantitative Health Sciences and Medicine, University of Massachusetts Medical School
Michael F. Collins does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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The U.S. faces one of the most consequential public health campaigns in history right now: to vaccinate the population against COVID-19 and, especially, to get shots into the arms of people who cannot easily navigate getting vaccinated on their own.
Time is of the essence. As new, potentially more dangerous variants of this coronavirus spread to new regions, widespread vaccination is one of the most powerful and effective ways to slow, if not stop, the virus’s spread.
Mobilizing large “vaccine corps” could help to meet this urgent need.
We’re testing that concept right now at the University of Massachusetts Medical School, where I am the chancellor. So far, 500 of our students and hundreds of community members have volunteered for vaccine corps roles. Our graduate nursing and medical students, under the direction of local public health leaders, have already been vaccinating first responders and vulnerable populations, demonstrating that a vaccine corps can be a force multiplier for resource-strained departments of public health.
On Feb. 16, we will help to launch a large-scale vaccination site in Worcester, where as many as 2,000 people could be inoculated per day.
Importantly, a large vaccination corps that includes local medical and public health students could help reach residents who might be missed by public campaigns and hospital outreach efforts. Students often represent their region’s races, ethnicities and backgrounds, which can make it easier for them to connect with communities that are hard to reach and might not trust vaccination.
The problem of getting people vaccinated quickly isn’t just about supply – it’s also about having enough people to carry out vaccinations, particularly in hard-to-reach communities.
If quickly mobilized on a large scale, a vaccine corps could directly meet three important challenges: accelerating the nationwide rollout of COVID-19 vaccines, ensuring that doses are distributed equitably to all and delivering on the promise that all Americans are able to benefit from major medical and public health advances.
Medical, nursing, pharmacy and other health students, as well as retired or unemployed clinicians, could deliver shots, monitor people who were just vaccinated or schedule the second doses that are required for the Pfizer and Moderna vaccines to be fully effective.
In particular, a large, well-organized vaccine corps could play a crucial role in reaching out to communities that are underserved, overlooked or hard to reach.
Corps members could staff phone banks to help people who lack internet or struggle to use online scheduling systems find vaccines in their areas and make appointments.
Our students in the vaccine corps have already helped administer vaccines in public housing complexes and homeless and domestic violence shelters. They could also provide transportation to vaccination sites or take doses directly to homebound elders who cannot safely venture out. In Alaska, for example, vaccine providers have been going out by plane and sled to remote villages to reach thousands of residents.
Members of a vaccination corps who share race or ethnicity with the community can also have an impact on overcoming people’s concerns about getting the vaccine. That’s important.
A poll released Feb. 10, conducted by the Associated Press and NORC Center for Public Affairs Research, found that only 57% of Black U.S. residents said they would definitely or probably get the COVID-19 vaccine, compared to 65% of Americans who identified as Hispanic and 68% as white. Fewer than half of Black Americans surveyed in a separate Kaiser Family Foundation poll in late January believed the needs of Black people were being taken into account.
Rural areas face similar concerns, as well as the geographical challenges of reaching people in remote areas. The Kaiser Family Foundation has found that people who live in rural areas are “among the most vaccine hesitant groups.” In mid-January, it found that 29% of rural Americans surveyed either definitely did not want to get the vaccine or said they would do so only if required.
If we extrapolate these vaccine hesitancy survey results, suggesting that as many as three or four out of every 10 Americans may avoid inoculation, public health officials’ hopes of reaching herd immunity will be in jeopardy.
The U.S. has a long history of creating health corps. After the Sept. 11 attacks, the federal government launched the volunteer Medical Reserve Corps to mobilize current and former medical professionals and others with needed health skills during emergencies. Several Medical Reserve Corps units around the country are now assisting vaccination efforts.
This concept could be expanded, including by partnering with universities, to have wider, game-changing reach. The model of service our students are testing opens up many possibilities, limited only by a lack of will and imagination.
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The US government’s $44 million vaccine rollout website was a predictable mess – here’s how to fix the broken process behind it

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Associate Professor of Operations Management & Business Analytics, Johns Hopkins Carey Business School, Johns Hopkins University School of Nursing
Tinglong Dai does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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The COVID-19 vaccine rollout has been a nightmare for many Americans as they struggle through multi-step registration and appointment systems.
The federal government had envisioned states using one national vaccine scheduling system, and it offered a contractor US$44 million to develop it. But that system turned out to be so poorly designed that all but nine states opted out before even trying to adopt it, even though it was being offered by the government for free.
The few states that do use the Vaccine Administration Management System, or VAMS, have reported random appointment cancellations and unreliable registrations. Some vaccinators have had to resort to creating records on paper because of system glitches, slowing down the pace of getting shots into people’s arms.
As troubled as the VAMS website may be, it is also a predictable result. We’ve seen this movie before.
HealthCare.gov, the federal healthcare exchange website that was launched to implement the Affordable Care Act, also known as Obamacare, cost taxpayers nearly $1 billion. When HealthCare.gov was launched on Oct. 1, 2013, only six people were able to sign up for health care on the first day. The Obama administration ended up having to enlist a team of engineers from Google, Amazon and Facebook to fix it.
The U.S. is among the most technologically advanced nations in the world, with some of the most powerful technology giants and the largest talent pool. So, why has the federal government repeatedly failed to deliver a functioning website essential to public health?
As an expert in health care operations management and contracting, I believe the complex federal contracting process bears much of the blame. The Biden administration has the power to fix it.
The U.S. government is the largest buyer on Earth. It spends more than half a trillion dollars a year procuring a wide range of goods and services from the private sector.
While private buyers may have their own rules governing purchasing, the U.S. government has to follow a set of procurement regulations. These regulations are known as the Federal Acquisition Regulations, or FAR, and they have been in place since 1983. The rules dictate all aspects of the federal purchasing process, including the contracting process for building websites such as HealthCare.gov and VAMS.
The Federal Acquisition Regulations were created to uphold the federal government and taxpayers’ interests through a uniform set of rules. Despite its good intention, this process has three key problems.
First, with thousands of clauses that are difficult to navigate, the Federal Acquisition Regulations have created a complicated and time-consuming contracting process, and many of those clauses are nearly impossible to implement in practice. That restricts the government to using a small group of vendors who are experienced in the game of contracting but are not necessarily the best choices for delivering products.
When the government announced the HealthCare.gov project, the tech giants that were eventually called in to fix it did not even participate in the bidding process, because the process favors past vendors such as CGI Federal, which specialized in federal contracting.
Second, in many cases, the complicated nature of the rules enables vendors to be selected without competition. In choosing a vendor for developing VAMS, the Centers for Disease Control and Prevention determined that Deloitte was the only contractor that met the project requirements. The reason: The CDC believed VAMS required GovConnect, which is Deloitte’s propriety platform. The GovConnect platform was launched in June 2020 and has had some problems. It is not clear why a vaccine rollout platform had to be built on GovConnect.
Third, the contracting process discourages communications and interactions between vendors and contracting officers. For websites like HealthCare.gov and VAMS that have many stakeholders, the needs of those stakeholders typically evolve during the development process. Companies such as Google, Amazon and Facebook use an “agile” method designed for changes during development. The current federal acquisition process naturally supports a traditional “waterfall” model that largely specifies all requirements at the beginning and allows little room for change.
How can the federal contracting process be fixed? Repealing the Federal Acquisition Regulations would likely cause chaos, but fixing it is doable. The executive branch of the U.S. government can modify the Federal Acquisition Regulations on its own, so it is up to the Biden administration to make changes.
Next, the federal contracting process must value results, not only the process itself or the vendors’ history of winning federal contracts. Deloitte and CGI Federal both continue to win federal contracts worth billions of dollars despite past failures.
VAMS has sparked far less public outcry than HealthCare.gov, but its failure is no less consequential, because a rapid vaccine rollout is the key to ending the ongoing COVID-19 pandemic. Deloitte spokesman Austin Price told Bloomberg News the company “continues to enhance the system based on feedback and priorities of VAMS users.”
The Obama administration started some reforms of the federal contracting system, particularly moving it away from the “waterfall” approach to allow more changes during development. The Biden administration could continue that work as it rethinks the tangle of federal contracting rules.
Unless it fixes the outdated federal contracting process, the U.S. will almost certainly repeat the same disaster again and again.
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How can I get the COVID-19 vaccine? Here’s what you need to know and which state strategies are working

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Associate Dean for Clinical Affairs, University of Southern California
Steven W. Chen receives funding from the Los Angeles County Department of Public Health in partnership with the Centers for Disease Control and Prevention 1817 Wellness Grant.

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For many people, trying to get the COVID-19 vaccine has been a lesson in frustration. The vaccine supply is limited in many areas, creating confusion over who can get a first and sometimes second dose of vaccine. Even when given the green light because of their age or occupation, many Americans have no idea how to go about getting vaccinated.
Nationwide, 6 in 10 older adults reported in a recent survey that they didn’t have enough information to know when or where they could get the vaccine. Those that do locate appointment systems are often finding them hard to use, and some have faced cancellations.
The Biden administration has promised to help alleviate some of the underlying problems, particularly vaccine shortages in some areas and inconsistent deliveries that have upended appointment scheduling. But the federal government doesn’t control the vaccination process within states or communication about it, and many states have pushed those decisions to understaffed counties. Currently, fewer than two-thirds of all vaccine doses distributed to the states have been administered, suggesting the problems go beyond supply shortages.
Some states are doing better than others, and they can offer lessons for the rest. And another Biden administration proposal could also soon connect more people with the vaccine and improve communication: activating more pharmacies to help.
As a pharmacy professor, I have been following developments in the U.S. vaccination effort. Here’s what you need to know.
Unfortunately, there isn’t one satisfying answer to this question right now. The federal government recommended priorities based primarily on age, preexisting health conditions and jobs that create a greater risk of exposure, like medical personnel. But states are following through in different ways.
To find your state’s information, you can check the Centers for Disease Control and Prevention’s list of state links. Or enter the name of your state and “COVID vaccine” in your favorite search engine to find out whether your state has a centralized process or whether each county or city maintains its own priority system.
States that centralize their COVID-19 vaccination procedures generally match registrants with available vaccine providers, as New Mexico and California do. If your state does not centralize vaccination procedures, you’ll need to look up the details for your county or city. Even within the same state, who is allowed to receive vaccinations and how to get one can vary widely.
A few states that have done well with vaccinations can offer lessons for the rest.
West Virginia vaccinated all of its long-term care residents and staff who wanted the vaccine within three weeks and started on second doses before other states had finished the first round. It had been the only state to opt out of the federal vaccination partnership with CVS and Walgreens for long-term care residents, instead relying primarily on a network of independent pharmacies.
The state also centralized vaccine decisions, coordination and registration at the state level rather than having West Virginia counties and localities come up with their own rules and processes. This eliminated a lot of the confusing messages and conflicting priority lists. Not everything was perfect. There were still problems with canceled appointments, particularly for groups using a troubled new appointment management system created for the CDC called the Vaccine Administration Management System.

North Dakota, which has had one of the highest COVID-19 case rates in the nation, expanded its priority list early to include anyone 65 and older, as well as adults with at least two high-risk medical conditions and front-line school or child care workers. It maintained its own warehouse to store and manage vaccine supplies, which allowed it to more easily send vaccine to providers across the state instead of only hospitals and health systems, as most other states were doing. It also deployed independent pharmacies to vaccinate people in long-term care facilities.
New Mexico credits its success in large part to a website that matches registrants with providers who have available vaccine and arranges appointments accordingly.
These three states have small populations, making the logistics somewhat simpler than in more populous states, but their approaches to vaccinating residents have worked.
Looking outside the U.S., Israel leads the world by far in vaccination rates, having vaccinated over half of its 9 million citizens. A strong public health system that treated vaccination efforts as a national security issue was key. Early preparation including aggressive acquisition of vaccines and allowing anyone over 60 to be vaccinated were also important strategies.
In many states, local pharmacies remain an untapped community resource for vaccination information.
With about 67,000 sites across the U.S., community pharmacies are highly accessible and experienced at administering vaccines due to their long history of providing vaccinations for flu and other preventable illnesses.
They also have established relationships with the communities they serve, often with staff who reflect the community’s ethnicities. This is critically important for improving the low vaccination rates among minorities.
And they have had continuing contact with people during the pandemic. Many patients have been unable or unwilling to see their medical providers as often during the pandemic, but they still pick up their medications and interact with their pharmacies.
States and counties can leverage this relationship to reach patients with information about when and how they can be vaccinated. Pharmacists have access to older and underserved patients who may have difficulty accessing and navigating websites. They can also help address questions about the vaccines from people who may be concerned after hearing rumors and misinformation. If people aren’t getting vaccinated, that could put herd immunity and a return to normal in jeopardy.
Vaccination is critical to slow the spread of new and more contagious virus variants and hopefully prevent the development of vaccine-resistant mutations. The president’s plan includes securing enough Pfizer and Moderna vaccines for everyone in the U.S. to receive both doses by the end of summer, provided the doses are distributed effectively.
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