Science Corner

How Vaccines Work (and What That Means for COVID-19)

How vaccines work, and what it means for COVID-19 – image of an injection in someone's arm

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.

Booster shots

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.

Source: BC Center for Disease Control Immunization Competency Course

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50 thoughts on “How Vaccines Work (and What That Means for COVID-19)”

  1. Thanks so very much for this information. I knew some of this already, but I wasn’t sure why it’s so hard to create vaccines if the virus is known. I mean, I seriously thought, why not inactivate the coronavirus and inject it? Obviously now that’s oversimplified.

    1. Yeah getting the right combination of different elements involved takes some trial and error, and then even once they’ve got something, even if it turns out to be the right thing, it requires time for clinical trials to show how long the vaccine actually gives protection for.

  2. Another fantastic post. I probably learn more reading your posts than anybody elses. Can’t wait to bore people with this information that they’ll just ignore so they can go eat a cheesburger in close company.

  3. Great post. I think Covid-19 has so many different strains we are seeing too, makes it quite troublesome. A lot of virus we get we also seem to be immune to it once we get it or say a vaccine for it, they don’t even know if you can become immune to Covid 19. Which makes me question…if we get a vaccine will it actually work truly?

    Off topic…but something else people seem to get confused about when it comes to vaccinations is some people believe once they get that vaccine for said virus or disease, than they won’t get said virus or disease. When in fact that is not entirely true. You can still get the flu after a flu shot, it just won’t be as extreme symtoms as if you were to get the flu with no flu shot. It like starts already preparing antibodis for your body to fight it and help symptoms lessen and heal much faster. I know a friend who had the chicken pox and shingles vaccine…she still got chicken pox and she then later still got shingles. It just was not the extreme case of either.

      1. Haha! That’s true, but they’re on a spectrum and anti-vaccination people are definitely at the extreme end. For example if you read comments on any news article about the virus, you never see any extreme views like that anywhere near the top of the list when you sort comments by popularity. Most people are definitely in favour of science and encouraging scientists to develop a vaccination.

        People like that will have always existed, and now they have more of a voice because of the internet. But the internet is also an incredible tool for reducing ignorance, at the same time. I’m sure the overwhelming effect of the internet up to now has been to reduce ignorance.

        That’s just my intuitive feeling, but that’s also an open debate in my mind that is relevant when these things are discussed. What I mean is, that’s the sort of question that I think should be asked and discussed.

        1. All the conspiracy theories have an impact too, like the people who think the coronavirus was manufactured in a lab. And then there are the people who are out protesting because they should be able to have a haircut. So I think all kinds of people besides the people who were anti-vax to begin with might dogpile in on this.

          1. Yeah, I agree. I was really referring to the total collection of people who would be mad enough to go along with it by any route, once all of the secondary influencing has been accounted for too.

            But, I suppose I will eat my words, and I’m probably being naive. There certainly seems to be a significant amount of people mad enough to go to packed beaches just because it’s sunny when there’s a virus πŸ€¦β€β™‚οΈ. Significant enough that I’m sure we’re gunna have a decent second wave! πŸ€¦β€β™‚οΈ

            1. There’s some of that going on in Canada, but it seems like the U.S. is really going all out ignoring the virus.

            2. Hahaha! We’re soon going to have a league table of the stupidest countries in the world. Those top countries will no longer have a leg to stand on when criticising their even dumber governments! It truly will be the population that is responsible for a lot of incompetence and stupidity. Remarkable, when we’re so used to drawling a line between a country’s government and its people on a lot of subjects.

            3. Yup. It’s rare you can point to a specific national behaviour and point an entire country out as objectively stupid, though. I say ‘entire’, I mean a good fraction of it, as opposed to the small group of powerful and corrupt/stupid people in positions of power.

            4. Oh for sure, sorry, there’s a misunderstanding. I just mean you can’t condemn a population by the actions of its government, usually, as often the wishes of the population are different to the government’s actions, regardless of how many stupid people there may be.

              But in this case saying that the country is doing a particular thingβ€” e.g. the UK is handling lockdown badlyβ€” actually applies to the country as a whole! And both the government and population have clear responsibility in this case.

  4. This was a very informative and interesting read – thanks very much for sharing it! It’s been hard to keep track of all the different vaccine stories and theories out there.

  5. I was a tad surprised that 1 of my white Instagram friends who has schizophrenia posted a “let us choose to be vaccinated against covid-19 or not” and equated it to being forcibly medicated for psychosis. I can see where she’s coming from…individual autonomy, trauma etc AND I feel strongly that people should be vaccinated, so I didn’t say anything because I didn’t know what to say…

    1. I don’t think there’s any way they could force a needle in someone for a vaccine, but what could possibly happen is limiting what people coould do if they don’t have the vaccine, which would make it the iniviidual’s choice as to what’s worse for them.

  6. Also I’m now a month overdue for my 3rd HPV booster shot, because of the lockdown, so I maybe I won’t be vaccinated against the HPV strains?

    1. I just looked it up on the US CDC website, and they say there’s no maximum allowable interval between the second and the third shots.

      1. I can’t remember which HPV vaccine I got, just that my gynaecologist said it was the “cheap” one. Cheap for her but it cost me $300, which is two months of food…

        1. Yikes. I never got it. As kind of an old fart, a) I’ve probably already been exposed to it, and b) my getting laid years are in the past, so that takes care of that πŸ˜‰

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