We all remain hopeful that a safe and effective vaccine to protect us from infection by the SARS-CoV-2 virus will be available within a year. This is far from certain, however, there reportedly have been promising results in early trials (we know little more than what has been in press releases because results of these studies have not been published in peer-reviewed medical literature yet). It is also promising that more than 150 vaccines, using different components of the virus to stimulate the immune response and different adjuvants that may enhance the immune response and prolong the immunity are being investigated. With so many variations undergoing trials, it offers hope that we may even have a variety of vaccines to choose from for our patients that can be tailored to their particular circumstances (e.g., we cannot use live vaccines in patients who are immunocompromised, and sometimes we find certain vaccines are more effective than others in children or in the elderly).
There remain many questions about these potential vaccines:
- When will we have a vaccine?
There has been speculation that we could have a vaccine this fall, perhaps as early as October. That would be wonderful, but very hard to believe. And, when people talk about a date that a vaccine may be available, we really need to be clear about what that means. Is that the date clinical studies conclude that the vaccine is safe and effective? Is it the date when the FDA approves the vaccine? Is it the date when manufacturing of the vaccine begins? Is it the date the vaccine is ready for distribution? Is it the date that the vaccine will be in pharmacies and doctors’ offices? The time over which these events transpire can very well be many months.
2. Will there be a sufficient supply of vaccine?
Given that the entire world will need the vaccine, it is widely believed that there will be limited amounts of vaccine available for some time until enough can be produced. The type of vaccine impacts how difficult it is to produce the vaccine and how long it will take. Given this, the state of Idaho is already beginning to determine priority levels for the vaccine. It is anticipated that vaccine will be prioritized to first responders, health care workers and high-risk individuals. So, when we asked above when the vaccine will be available, another question is when will it be broadly available to the public, as opposed to limited in supply such that it must be prioritized and rationed?
3. How many doses of vaccine will be required?
We don’t yet know. It appears that there is one vaccine that may only require a single dose, but it seems likely that most of the others will require a series of two injections a month apart. This has important implications. First of all, compliance with a two-vaccine series would be anticipated to be less than that of a single vaccination. Secondly, a two-series vaccine would generally be more expensive than a single dose vaccine, and cost may create a barrier to immunization. Finally, given the few manufacturers of vaccine syringes and needles and the anticipated increased demand for influenza vaccine, as well routine vaccinations for children, we might encounter shortages, particularly if the coronavirus vaccine requires a two-injection series.
4. How often will vaccination be required?
Unfortunately, recent studies suggest that the antibody response to natural infection with SARS-CoV-2 virus is very short-lived and that it is very possible that as many as 79 percent of those infected do not generate protective antibodies. There certainly is the potential to produce vaccines that will stimulate an improved immune response with the production of neutralizing antibodies, in addition to other immune enhancing effects, and it is possible that we may be able to promote more durability of the immune response with the right adjuvant. Nevertheless, it is very likely that we are looking at the potential of people needing an annual vaccination or perhaps a booster every two to three years.
5. Will the vaccine be effective in the elderly and immunocompromised patients?
There is a senescence of the immune response with increasing age. We will have to determine whether vaccines generate a sufficient immune response in the elderly, whether they require a stronger dose or perhaps more doses more frequently. Immunocompromised patients generally are not able to be given attenuated live vaccines, so we will need other options, and in fact, there are quite a number of other types of vaccines being studied. How effective those other vaccines are will likely depend upon the nature of the underlying immune deficiency.
6. How critical is IgA to the immune response and protection from SARS-CoV-2, and will the vaccine provoke an IgA response?
What we hear about in the press and media about “antibody tests” are tests that detect the presence of IgG, a type of antibody that is available to attack virus in the blood. However, IgG has two important limitations. It is ineffective at attacking viruses once they enter into a cell, and it is ineffective at attacking virus in tissues, especially the lining of the gut. IgA fulfills the latter role.
This is an important issue because the SARS-CoV-2 virus attaches to a receptor called ACE-2. That protein receptor is in the lining of the nasopharynx, the lungs and the gut. Currently, we believe that the target of the initial infection is the nasopharynx, but can the entryway for infection be the gut? Is IgA important in the defense from infection with this virus, as it is for certain other viruses, like polio? Will the vaccine trigger a sufficient IgA response?
The vaccine development for protection from the SARS-CoV-2 virus is encouraging, but far from certain. There remain many questions. No doubt we will get answers to many of these questions soon.