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Asked by anon-255955 on 1 Jun 2020.
Question: Why do vaccines take as long as they do to enter circulation?
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Alena Pance answered on 1 Jun 2020:
Hi Jack,
It’s not necessarily that they take very long to enter circulation, it’s more to do with the immune system responding to the vaccine that takes some time. This is because the vaccine, or antigen, needs to be taken in by the cells of the immune system and processed so that the cell, depending on which one it is, can make antibodies specific to the vaccine (these are B lymphocytes) or become primed to kill the pathogen directly (these are NK cells, T lymphocytes, amongst others). This recognition of the vaccine takes time to ultimately generate the so called memory cells that will survey the body to be prepared for a potential encounter with a pathogen.
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Alex Holmes answered on 1 Jun 2020:
Hi Jack! I’m going to assume you mean enter circulation in terms of the population rather than the blood stream.
Vaccines can take a while to go from initial concepts through to the final product that’s given out in clinics because they have to go through a lot of testing to make sure they’re safe and to make sure that they’re effective, each of which can take months or even years of clinical trials (where healthy and then later ill people are given a potential treatment). So, you can see how this time adds up. Luckily for covid-19, due to demand these trials are mostly happening simultaneously, which speeds things up!
There’s also then the question of manufacturing the vaccine: do we have the right “recipe” and protocol? Do we know how long each vial lasts before it goes off or becomes less effective? how best do we store and transport them? It’s one thing to say it needs to be refrigerated at all times until use, but what if it’s needed in areas without electricity? Manufacturing might seem as easy as just telling a factory to start, but it can take a long time to build up a large enough amount to release to clinics – months to years again. It’s a risk for companies to start manufacturing early – even during the trial period because if it fails testing, you then have a large expensive stock of stuff you can’t sell so they’re reluctant to do it. Luckily for covid-19, other companies and individuals have taken this risk on behalf of companies and researchers and are paying for large scale manufacturing before the vaccine has completed testing so that as soon as the scientists agree it’s safe and it’s licensed, it can go directly into circulation!!
I hope that answers your question 🙂
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Emma Daniels answered on 1 Jun 2020:
Hi Jack, great question! Alena has written a great answer about how vaccines and drugs can take a while to take effect in our body. I was wondering whether your question could also mean why does it take so long to get a vaccine into the market, and to a point when it can be used by people? This is because all drugs and vaccines have to go through a rigorous testing process. First an effective drug/vaccine needs to be identified, which could involve testing hundreds or even thousands of compounds before finding an effective one. Once found, it needs to go through pre-clincal trials. This is when the drug/vaccine is tested using computer models, in specially grown cells, and in animals. They then have to go through clinical trails, when they are tested in humans. After all that, a drug/vaccine has to be approved by governing bodies, such as the FDA (food and drug administration). All in all, this process can take ~10 years! GSK have more info on how the develop new medicines here: https://www.gsk.com/en-gb/research-and-development/development/how-we-develop-new-medicines/
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Sabrina Slater answered on 1 Jun 2020:
Hey Jack,
An important question! The best way to answer it is to walk you through the stages scientists have to go through to “create” a vaccine.1) DESIGN: we have to find the parts of the nasty causing infections (normally a virus) that our immune systems will recognise, but not overreact to. This bit can be based on our knowledge of other viruses or may have to be found out from scratch. There are also groups of vaccines called “live” or “heat killed” vaccines, where the whole virus is changed slightly so that it’s no longer infectious, or (you guessed it) killed by boiling it so that it’s still whole but “dead”. These heat-killed vaccines aren’t really a thing any more, because scientists have found better ways to show only the important bits of the virus to the human immune system. As an estimate, if we knew absolutely nothing about the virus before starting because it looks nothing like anything we’ve ever seen before, this could take years. Luckily for most viruses we know who they are… or at least, we’ve met one of their cousins 🙂
2) PRE-CLINICAL TESTING part I: like the design stage, this bit is also done in the lab. Here we test whether the bit of the virus we’ve chosen is recognised by the right immune cells, because if it is, it means it can be given to animals or humans. This can take months. If it isn’t, we have to go back to the design stage. To even get to this step we have to make sure we can manufacture the bits of the virus on a small scale (this is almost “the vaccine”), which can also take months to get right.
3) PRE-CLINICAL TESTING part II: the aim of this stage is to make sure the virus is protective to other animals. That means, if we give a small dose of our bits of virus to a lab animal in a controlled way, then infect them with the virus, how do they react? We basically want them to be protected from the virus and not show any side-effects. This part also takes months. And as before, if it doesn’t work, it’s back to step 1!
4) CLINICAL TRIALS part 1: You might see this called “phase I trials” in some places. Here, once we’ve checked our “virus bits” all work they way they should in the dish and in animal models, we give our newfound “vaccine” to healthy human volunteers in regulated doses. The aim here is just to make sure it’s as safe as we thought it was, and gives us an idea of what kind of dose we would give to future patients. We have to add some things here to make sure the vaccine doesn’t go off, that it’s a liquid (that helps!), and that it’s in a form that can be safely recognised by the human body. It’s worth mentioning that in the UK we are not allowed to pay people to take part in any sort of clinical trial, so these people are true volunteers.
5) CLINICAL TRIALS part 2 (aka phase II trials): We give the vaccine at the dose we figured out in step 4 to a bigger group of people, maybe this time including people from different ages, ethnic backgrounds and health backgrounds, so that we can get a good picture of how lots of different people might react. We look after them carefully and note down any reactions, good or bad, that they have. Step 4 and 5 together take months to monitor the volunteers and review all the symptoms they tell us about. We might need to stay in touch with them for many years to make sure nothing changes about what they initially told us. So already we’re talking more than a year since step 1!
6) IMMUNISATION (aka phase III trials): Now that we know the vaccine is safe, we need to make sure it actually protects us against the disease the virus causes! We next give the vaccine to lots of people and keep a close eye on the number of people who then get infected. Don’t forget, this whole time we’ve spent a lot of money and time trying to get enough of the vaccine manufactured to give to all these people, and we need make EVEN MORE to keep going far enough to immunise an entire population. Again, this can take years to make sure everything works as we think it should.
Some of these steps can be shortened with knowledge of different vaccines, but at the end of the day, it’s human lives we’re talking about, so we can’t cut corners! Part of our job as scientists is to be as open as possible with our knowledge so that people understand what vaccines are and why they’re probably one of humankind’s greatest invention!
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