Great news has been released in the past two weeks. There are multiple vaccines that are emerging and preliminary results (from Phase III clinical trials) show that at least two are 95% effective. But what exactly does that mean? And why is it better to get the vaccine instead of just getting COVID-19 out in the wild, besides the obvious reasons?
Specifically, what prompted me to write this post was that my fellow Skepchick Jamie Bernstein had some questions, paraphrased below:
- If a vaccine is stated to be 95% effective, does that mean only within the ideal conditions of the study (i.e. in a world where everyone is social-distancing and wearing masks)? So, in the real world, would it still be as effective?
- Does “95% effective” mean that you have a 95% chance of not getting the virus every time you are exposed?
Let me explain how they derive the 95% effectiveness. Tens of thousands of people were enrolled in each study (I believe they tried to recruit in cities and other places that were possible hot-spots to maximize exposure to minimize the total time needed for the trial). Half of the people got the vaccine, the others got a placebo shot. Then, we just wait and see who gets sick. The FDA said the vaccine trial needs at least 165 people to get sick, which doesn’t seem like a lot but I don’t believe either trial has hit that number yet (with the way the cases are coming in though it might be soon). Then they see, of the people who got sick in the trial, how many received the vaccine? The number of people who got sick who didn’t receive the vaccine versus the ones who did is basically how you calculate effectiveness.
Specifically in the Moderna trial, there were 30,000 people enrolled, and there were 95 CONFIRMED positive cases (had at least 2 symptoms plus a positive test, and for Moderna they ONLY counted cases that were at least 14 days post the second shot, which was 28 days from the first shot, so PLENTY of time to have a proper immune response, since there is a lag time between when you take a vaccine and when your body is prepared). Out of the 95 people who got sick, only 5 had received the vaccine, so it is 94.7% effective.
Ideally, the participants are split up in the study such that the risk for everyone will be the same (I know they tried to recruit a diverse population too, including race, sex, age, but don’t know all of the details). So, even though many people wear masks and social distance, in a population that size, there are plenty that don’t adhere to those rules, at least not perfectly all the time.
Would the vaccine be less effective if we all weren’t wearing masks and distancing? Highly doubtful. Normally, your immune system is great at absolutely crushing antigens it has previously identified as hostile.
Let me explain a little about how your body makes antibodies:
There are immune cells that are patrolling your body at all times looking for things that are not identified as YOU (via proteins on the surface). When they find something, they take little pieces of it and send it through your lymph system to essentially the immune central processing unit. Imagine that the surface of an antigen is covered with one type of lock–what your body does is essentially generate every type of key in the universe and try it in the lock until one fits. And as soon as one does, your body scales up this reaction and generates MILLIONS of these keys (these are the antibodies), then releases them throughout your body, where they stick to the surface of the antigen, thus tagging it as “NOT YOU”. When the other immune cells see this tag, they just go out and kill anything with an antibody stuck to it. And even though your antibodies in the blood stream will fade over time, certain immune cells remain that will be able to identify this antigen should it ever darken your doorstep again.
The graph below shows you the difference in response during a normal immune reaction. The time between initial exposure and the peak of the primary immune response can be 7-14 days. The time between SECONDARY exposure and the peak of the secondary immune response is much shorter, approximately 1-3 days. (These times are approximate, each antigen generates a different reaction, but you get the general point.)
So once you are vaccinated, your body is very good at quickly generating that secondary immune response and that’s why you generally don’t get sick from the same antigen twice (barring immune system issues). Now, why do we have a flu vaccine every year? Because the proteins on the surface of the antigen mutate just enough to make your body have to re-generate all new antibodies. Some antigens change faster than others, especially if they are allowed to infect people unchecked.
Why don’t we just allow herd immunity to happen instead of the vaccine? I mean, of course we know that by allowing people to get sick, specifically with regards to COVID-19, that will overwhelm the hospital system and a lot of people would die needlessly. But there’s also another complication that isn’t as visible: the vaccine allows for a more controlled immune response and there is a much lower chance of you getting an immune disease. Earlier, when I said that your body generates antibodies (keys) to fit a lock on the surface of the antigen, well sometimes the antigen surface resembles something else inside of your body, and now in addition to crushing the antigen, your body is also attacking itself, which can cause some of these long-term COVID-19 effects that we are seeing (speculative but I’ve seen journal papers mentioning it). This concept is called “molecular mimicry” and it’s the same reason that you can get bitten by a tick, develop Rocky Mountain Fever, and then develop an allergy to red meat. Or you get a virus and get better but end up with Type I Diabetes because your body attacked pancreatic cells. And the final issue is that we don’t know the long-term effects of getting COVID-19, because who knows what could emerge years later.
A big exception to what I’ve said is this: we know how the immune system NORMALLY works. But we just don’t know enough to say how the reaction will be specifically with regards to the COVID-19 virus, and how long people will be immune for, etc. Ideally though, your immune system will react in a predictable way as with most things.