While COVID-19 is caused by a novel coronavirus, and there’s still much to be learned about the virus and the illness, coming up with a vaccine doesn’t mean totally reinventing the wheel. How vaccines work is based on knowledge about how the immune system works, and the immune system doesn’t abruptly change just because a new virus comes along.
So, in the spirit of fighting misinformation, here’s a quick primer on how vaccines work.
The immune system in a nutshell
When a pathogen (e.g. a virus, bacterium, or fungus) enters the body, the immune system kicks into gear. The first part of the response is non-specific, meaning it doesn’t depend on what the particular invader is.
A little bit later on in the process, a component of the immune system called B cells take a look at the pathogen to see if they recognize it. If they do, they can start pumping out antibodies that match that pathogen. If not, they’ll build brand new antibodies. These Y-shaped proteins lock onto the pathogen, and this allows the body to clear the invader more effectively.
After exposure, B cells retain some degree of “memory” for the invader, and antibodies can hang around for a while and may provide some protection from future exposures. The extent of this can vary from one pathogen to another. The novel coronavirus hasn’t been around long enough to have a clear picture of this.
Antibody tests have been getting mentioned in the news recently, and when they’re effective (which will never be 100% of the time), they should tell you that you’ve been exposed to the virus and have produced antibodies. What’s still unknown, though, is what quantitative level of antibodies you need in order to be protected. If you’ve ever had antibody titers done to check if you have immunity for something, that’s the part that still hasn’t been figured out yet for the coronavirus. To use totally meaningless numbers, let’s say you have 5 antibodies after having had COVID-19. But if you need 500 antibodies to keep you from getting sick if you get exposed again, your 5 antibodies aren’t going to do much for you.
Vaccines are another way of activating the immune system to get it to produce antibodies. A version of the pathogen or its component parts is delivered into the body, often by injection, so that the immune system can do its thing and make enough pathogen-specific antibodies to keep you from getting sick if you get exposed to the real deal.
A temporary way to get immunity is called passive immunity, which comes from antibodies that you get from an external source, like breast milk or convalescent plasma (a blood product). Passive immunity is a short-term form of protection, as your body’s antibody-making factory doesn’t even start up the production line.
Types of vaccines
There are two broad types of vaccines. Live attenuated vaccines contain a form of the virus that’s able to replicate, but it’s been weakened so that it doesn’t cause illness. However, in people who are immunocompromised, these usually aren’t a good idea, because people can actually get sick, although not as sick as if they were exposed to the non-weakened virus. The measles-mumps-rubella (MMR) vaccine is an example of this type of vaccine.
Inactivated viruses can’t replicate, so they can’t make people sick. They contain a component of the virus that the body will build antibodies against. There are a number of different subtypes of inactivated vaccines.
Components of a vaccine
Besides the actual weakened or inactivated virus, several other components are required. It’s crucial that the immune system mount enough of a response to the vaccine to achieve sufficient antibody titers to maintain immunity; otherwise, it’s all just a waste of time. Therefore, various agents, including aluminum, may be included to enhance the immune response. There are also preservatives, antibiotics to prevent contamination during manufacturing, agents to inactivate the virus and any protein toxins, and pH buffers. While some items on the ingredient list may sound scary, the amount in which they’re present is extremely small.
The viral components in vaccines are often reproduced in egg embryo cells, which act as little vaccine component factories. The risk of an allergic reaction to a vaccine is low, and even people with egg allergies can often get vaccines, but whoever is administering the vaccine will always have a supply of epinephrine on hand to manage an allergic reaction.
Typically, a single dose of a vaccine doesn’t generate enough of an immune response to give long-term protection When you get the first dose, the body tends to produce mostly IgM-type antibodies, which don’t stick around that long. With subsequent doses, the body produces more IgG-type antibodies, which give more lasting protection. Booster shots give your body the opportunity to produce sufficient IgG antibodies to be fully protected.
Because vaccines generate an antibody response that’s highly specific to the particular antigen, they’re very specific in what illness they’ll protect you from. The key to the influenza response door isn’t going to do anything in the coronavirus response door.
What this means for COVID-19
While there’s a lot that isn’t known about COVID-19, the principles of how vaccines work and how the immune system works are still there. It’s a problem, though, when people who don’t have any of this background knowledge think their guess is as good as anything the scientists are doing, and misinformation starts flying around everywhere.
There are lots of different labs around the world working on coming up with a vaccine that works and is safe. Whether the first past the pose vaccine will involve weakened or inactivated virus, how it will be grown, and the number of doses that will be required, all remains to be seen. But all that baseline knowledge about vaccine development is still there.
Once a vaccine is available, it will be important that enough people get it to build up enough herd immunity to shut the virus down altogether. For highly contagious illnesses, a substantial portion of the population needs to have immunity, either from sufficient exposure or from a vaccine, to prevent uncontrolled spread. If not enough of your herd is immune, the pathogen can keep dancing around and doing its thing. Let’s just hope the anti-vaxxers aren’t able to mess this up.
For more on public health, visit The Science Corner: Debunking Pseudoscience.
Source: BC Center for Disease Control Immunization Competency Course – This isn’t as accessible as the sources I normally cite; the info comes from a learning module that’s required for nurses (like me) doing immunizations in my province.