Welcome to the Osmosis daily report on the coronavirus pandemic. I'm doctor Rishi Desai. I'm the chief medical officer at Osmosis.
I'm also pediatric infectious disease doctor, and I used to work at CDC in the division of viral diseases doing outbreak research.
So today we're gonna talk about how long immunity lasts, which has come up a lot in both the media as well as in
scientific circles. We're trying to figure out whether immunity is something we can lean on to decide who is able to reenter society.
There's this great paper that is entitled antibody responses to SARS-CoV-2, which is the virus that causes COVID-19,
and they try to answer this, and one of the things we have to answer is when do you show
antibodies if you're going to have immunity and they showed that the seroconversion rate,
which is the rate at which you start showing antibodies, starts to rise quickly in the first 2 weeks.
So 2 weeks after you get the infection you start getting that immune response and they showed that, overall in this
161
person group, about half of them had shown levels of antibody rising by day 11 and
everybody showed levels of antibody rising by day 39.
So in other words, between 1 and 2 months everybody in their study that was going to have an immune response did have one.
Now they also had this great table which is table 2 in their study and it shows the value of antibodies
to detect disease, you know, when you detect disease you talk about sensitivity and ideally you detect everybody that has disease.
That would be a sensitivity of a 100%,
but sometimes you miss folks and if you miss let's say one out of 100, that would be a sensitivity of 99%.
Here RNA sensitivity, using RNA testing, had a sensitivity of
67%. So they were missing
33 people with RNA testing. With antibody testing alone
They got 93%. So only missed about 7 out of a 100. And
Combined, if you look at RNA and antibody, you can see that sensitivity goes up to 99.4%.
So at that point, they're really missing just 1 out of a 100 on average.
So that's a pretty powerful way of using 2 different tests, the RNA test and the serology antibody tests together,
to catch as many people as possible, you get up to 99%.
Now we know that COVID-19 has only been around for a few months in humanity.
And so to really understand how long immunity
lasts, we know when you start showing an immune response, but to show how long it lasts, we have to look at potentially other
coronaviruses and there's this great study looking at SARS. So this is published back in 2007 and one of the key
conclusions that they reach, I want to just jump right into the conclusions here,
is that the general trend of IgM peaking at around 1 month after symptom onset and
IgG peaking 2-4 months after symptom onset
was consistent across different studies and they found that in this study too. I just mentioned that because we just talked about IgG peaking around
day 39, or at least that's when most people had a positive result. So with this other coronavirus again, this is SARS
not SARS-CoV-2, but with SARS it also kind of showed peaking in the first few months
let's say by month 4 in this case
Now why I think this study is so cool is that they have this graph and you can see now in the triangles.
This is the top line, the triangle show the IgG
positive percentage. You can see it peaks again, you know, between 90 and 120 days.
So this is month 3-4, but this is the beauty of this study because it happened, you know, over a decade ago
they've been able to follow people over time and you can see that even 1-2 years later,
the rates are still high, but then if you get past that if you get into year 3,
that's when you started seeing a big drop-off. In fact, that was their key finding here
is that somewhere around year 3 is where the immunity or the IgG level starts to fall.
Here's that same conclusion kind of in a table form. You can see IgG % positive samples
You can see it peaks again around day 120
or so is when you hit a hundred so it would be 4 months out and you can see it stays in the, you know,
93%-89%-90% range and then it drops down to 53%.
And this is out 3 years or so.
So this is where you're starting to see a huge drop-off and if you're curious IgM starts to fall off
right here in month 1-2.
So that's where the IgM level starts to fall down after kind of peaking around 76%
So that falls very early on, but the IgG level,
which is really what we're counting on to maintain a good immune response for SARS and other coronavirus,
we're seeing that a few years out. Now you can't really do this next study in humans, but they did do it in macaque,
rhesus macaque monkeys, and what they essentially did is they infected them,
got them sick with COVID-19, and then tried to
reinfect them, and let me just show you what they found when they tried to do that.
Now numbers matter and they only did this in a few macaque monkeys.
I think at the end of the day,
they only did two macaques that actually got reinfected and they showed that in these
monkeys from our current study, the reinfection could not occur if the monkeys produced the neutralizing antibody at an early stage
after primary infection,
which makes sense and it goes with kind of what we always believe, which is that if you have an antibody response there,
you're not likely to get infection again and this is shown in this study with monkeys.
They also allude to this other phenomenon of discharged patients coming back and testing positive.
In fact, this has been reported in the news and here they say,
you know, given that we know that an immune response occurs to COVID-19, they believe it's most likely that when that does happen,
It's probably because of false negatives and so they go and discuss this very briefly here in this paper.
It's a good segue to what happens when we read about these cases of people getting sick with COVID-19,
getting treated, going home, and then coming back and having the infection again. Is that really reinfection? That's the question?
Here's a headline from the "LA Times" that kind of gets right at this. It says: They survived the coronavirus. Then they tested positive
again. Why? Now based on what I just went over. We know that you get an antibody response. We know that you
generally can measure that with IgG levels and if they're high you shouldn't have
reinfection, at least we don't think so at least for a few years, and maybe at that point you'd need to get a
booster dose or something like that. If there's a vaccine maybe you need to revaccine at that point.
But at the moment, we think that immunity lasts for a few years. So in these cases, where we're seeing people reinfected, the most likely explanation,
and they allude to this actually down here, is that people are essentially going home and they're either false negative, meaning that they
thought that they cleared the infection but they didn't, and the test simply missed them.
Remember, we showed earlier that the RNA test to miss people and so maybe that's what's happening here
they're missing cases and
then going home thinking they've cleared the virus that they never had and they come back in sick again because maybe they never really
fully recovered. On the flip side,
maybe there are some false positives, maybe when they retest they thought that they were positive, the second time around,
but maybe they weren't, maybe they had something else and for whatever reason that test messed up and
told them they were positive when they weren't and that happens as well.
So it could be a false negative, could be a false positive, either way
what that gets through is it's a testing issue. The third possibility, and this is not mentioned in this article,
but I'm just suggesting it here, is that maybe these very few people have some sort of immune deficiency,
maybe they for whatever reason they're not mounting a good IgG response in the first place because remember,
we're not really measuring that at the moment in most cases
so maybe they never had a good IgG response and
therefore, they're actually prone to getting reinfected and that would be something unique to that person because of their own immune status.
So bottom line, what we believe is that with COVID-19 you do get a good immune response,
it lasts for a few
years and at that point maybe you need another vaccine, if that's available and likely there would be at that point,
or maybe you just get exposed again at that point and get, you know, a reboost in your immunity naturally.
But nevertheless, it does seem to last for a few years in these cases of reinfection.
Probably have more to do with testing making mistakes then actually saying disease go away and come back again.
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Thanks and be well.