Where is the SARS-CoV-2 vaccine, anyways? Part 1
In this first post, we’ll talk about what vaccines actually do, why there isn’t a SARS-CoV-2 vaccine yet, and what’s being done to develop one. In our upcoming Part 2 post, we’ll delve into the specifics of different SARS-CoV-2 vaccine approaches.
Our immune systems are adapted to fight a multitude of pathogens, but sometimes we need extra help. We use vaccines to limit the spread and severity of many pathogens. However, SARS-CoV-2 is a new pathogen and a vaccine has not yet been developed for public use. So why is it taking so long to make a vaccine for COVID-19?
Toddler about to receive a vaccine from a doctor. Credit: Photographer: Heather Hazzan; Wardrobe: Ronald Burton; Props: Campbell Pearson; Hair: Hide Suzuki; Makeup: Deanna Melluso at See Management. Shot on location at One Medical.
What is a vaccine?
A vaccine is a preparation of pathogen-derived biological substances (frequently an injectable solution) that generates an immune response against the target pathogen. In effect, a vaccine is a way to train your immune system to recognize a bad guy without needing to be attacked by one. An effective vaccine response establishes immune memory that can be rapidly mobilized upon future infection by the same pathogen. Immune memory doesn’t prevent us from being infected by the target pathogen, but it can substantially limit the severity and duration of the associated disease. Immune memory is also pathogen-specific, so, a completely new vaccine is required to generate immune memory to SARS-CoV-2. This is why we can’t use the influenza vaccine to control SARS-CoV-2 infections.
When a vaccine is administered to the majority of a population (a neighborhood, city, or country), the vaccinated population slows the spread of the infection and protects the vulnerable members of that population who cannot be vaccinated. This is called “herd immunity”. Every year, we develop new vaccines for different strains of influenza to establish herd immunity, so we don’t need to practice social distancing during every flu season.
Herd immunity animation. Source: Reddit.
Why don’t we have a vaccine against SARS-CoV-2 yet?
After years of influenza virus research, we are getting better at rapidly developing new annual flu vaccines with a pipeline of reagents and resources that can be easily adapted annually. However, this is possible because different strains of influenza harbor consistent and (somewhat) predictable changes. Conversely, SARS-CoV-2 is a new strain of coronavirus without an established vaccine development pipeline. Also, the distinct structure of the spike protein in SARS-CoV-2 adds a layer of complexity to the development of a new vaccine. Finally, many vaccine candidates fail clinical testing because the vaccine may not induce long-lasting immune memory and we can only measure this memory response in clinical trials.
An artistic rendition of coronavirus by David S. Goodsell.
Can we make a SARS-CoV-2 vaccine in time?
Although challenging, the timely development of a SARS-CoV-2 is possible. Several technological developments have hastened the rate of vaccine design, and preliminary observations suggest that humans can produce neutralizing antibodies to SARS-CoV-2. At present, at least a dozen different biotech companies, non-profit research organizations, and universities have announced COVID-19 vaccine programs, and a phase I clinical trial to evaluate the safety and efficacy of a SARS-CoV-2 vaccine (called mRNA-1273) recently launched in Seattle, Washington. Any vaccine candidate will need to pass several hurdles to be approved for broader public use. However, broad enthusiasm (and dire need) for new vaccine development increases the probability developing an effective vaccine within 12 to 18 months. Although that seems like a lot of time, we must critically assess all of our vaccine candidates to make sure that they can elicit effective long-term immunity before releasing each candidate for public use.
How do scientists determine if a vaccine works?
Immune memory can be measured by several different factors, but the production of virus-specific antibodies is often a good indication of virus-specific immunity. However, virus-specific antibodies alone do not necessarily provide protection from viral infection. More studies are needed to confirm these antibodies can prevent the propagation of the virus inside the patient and within populations. Virus-specific antibodies can be readily detected by several different assays in the lab, but the quality of protection arising from a particular vaccine can only be determined by monitoring a large population of vaccinated individuals over several months.
Closeup of a doctor’s hand, vaccine, and arm. Photographer: Heather Hazzan; Wardrobe: Ronald Burton; Props: Campbell Pearson; Hair: Hide Suzuki; Makeup: Deanna Melluso at See Management. Shot on location at One Medical.
If I get SARS-CoV-2, will I be protected from being re-infected?
A conventional immune response to infection does generate protective immune memory for many pathogens. However, there are some notable exceptions (immunity to mumps virus, respiratory syncytial virus, and pertussis wanes over time). At this point, it remains unknown if recovered COVID-19 patients have long-lasting immunity to reinfection with SARS-CoV-2 (to be discussed further in a future post). However, the severity of SARS-CoV-2 infection, and our limited clinical resources underscores the need for a safer method for acquiring SARS-CoV-2 immune memory through vaccination. Until this vaccine is ready and other treatments are available for public use, we may need to continue to practice social distancing to ease the burden of this disease on our healthcare system. Like you, we are all anxiously waiting for the SARS-CoV-2 vaccine, but a good vaccine is worth the wait.
Stay tuned for Part 2, where we’ll discuss the different SARS-CoV-2 vaccine candidates and what’s happening in clinical trials right now!
Phil Domeier, PhD
Phillip received his PhD in Virology and Immunology from Penn State College of Medicine in 2018, where he studied the immunological factors that promote pathogenic antibody production in Systemic Lupus Erythematosus (SLE). He is currently a postdoctoral fellow in the Ziegler Laboratory at the Benaroya Research Institute in Seattle, Washington. His current research aims to determine how genetic and environmental factors influence antibody production in patients with allergies and autoimmunity. Outside of the lab, Phillip enjoys snowboarding and hiking with his dog, Milo.