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[♪ INTRO]
So you show up for your annual physical and the doctor tells you you need a ten-year booster shot.
But you’ve already had all your routine vaccinations,
so what’s in that syringe that’s so important?
Well, the vaccines we have all do a pretty good job of introducing our
bodies to certain diseases and convincing our immune systems to take that threat seriously.
But for some diseases, it takes extra convincing. Which is why
you might need to get the same shot more than once -- weeks or even years later.
Vaccines teach our immune systems to recognize certain pathogens, or disease-causing agents.
In a nutshell, they trigger the formation of specialized cells and antibodies that
recognize the distinctive proteins that stick out of pathogens -- called antigens.
If something with one of those antigens shows its face, the antibodies latch on and disable it,
while those specialized cells help to kick it to the curb.
Now, there are a few vaccines that require multiple doses of the same
shot. And there are almost as many reasons for that as there are different vaccines.
Because how much immunity you get from a single shot, and how long it lasts, can really vary.
Some vaccines, like the Hepatitis A vaccine, tend to require
multiple doses to dial immunity up to the best possible levels when you first get them.
Others, like the shot that protects against tetanus,
require getting the same shot years later to dial immunity back up to full
throttle -- what we often call a booster shot, though the terminology can vary.
And scientists are learning that some vaccines, like the HPV vaccines,
may provide solid immunity for more than a decade with just
one shot -- even though their efficacy was first established using multiple doses.
Like I said, immunity can really vary
Immunology is notoriously complicated, and we’re still trying to understand the details
of how our existing vaccines work on a molecular level.
So, we’re still working out the right number of shots and when to give them.
In some cases, that even applies to diseases we’ve been vaccinating against for decades.
But in general, you might need to go back for a top-up because immunity
doesn’t always last forever.
Basically, over time, immunity to some threats can get sluggish as immune memories
get fuzzy and the numbers of specialized cells dwindle.
It seems to happen in tiny sites called germinal centers.
These form in the lymph nodes and spleen upon encountering a new antigen.
These centers are where immune cells hang out, maintain their numbers,
keep their memories sharp, and lie in wait in case their pathogen-of-interest shows up.
Those cells include the B cells that make antibodies, as well as T cells,
which are also thought to help remember past invaders.
When germinal centers form, specialized cells grab copies of the antigen
and B cells get to work testing out antibodies, keeping only the ones with the tightest grip.
How well immunity builds up in the first place, and the extent to which it wanes over time,
might depend largely on how efficiently this process goes down.
Immunologists are also still figuring out how time and the elements take a toll on how well
older people’s immune systems work to fight off pathogens that they’ve been vaccinated against.
Researchers are still working on how to tweak different vaccines to induce the
formation of the best germinal centers to get immunity to last as long as possible.
That said, we’re still learning how this all works!
Overall, though, whether we’ll need booster shots down the line depends on a few things,
like how much our immunity declines.
For example, people who contract measles once are considered immune for life.
And so are those who receive a pair of shots of the vaccine we’ve been giving since 1967.
Many people -- though not all -- will develop a robust immune response after just one shot.
The second dose just ensures that more people will be thoroughly protected.
Measles surface proteins aren’t good at mutating,
so the antibodies you make will keep recognizing them indefinitely.
But with other vaccines, our immune system needs a lot more help.
Like pertussis, better known as whooping cough.
In the 1980s, many countries started switching to a new version of this vaccine
that only contained pieces of the pathogen, instead of the full thing.
That was because the older vaccine that contained killed,
whole cells of the pathogen had occasional nasty side effects.
The problem is, researchers have realized more recently
that immunity from this cell-free vaccine wanes after just two years.
The current vaccination schedule calls for kids to get their first shot a few
months after their first birthday, and the second one after they turn four.
So it looks like our vaccination schedules will need to be updated
to keep people protected from pertussis outbreaks.
Now, what about the vaccines on everyone’s mind -- the ones for COVID-19?
Many of these vaccines are administered in a two-shot series, so the question is what,
if anything, we’ll need after that.
And right now, we’re just not sure. But scientists are working on it.
One manufacturer, Moderna, plans to begin testing booster doses of their current mRNA vaccine in
July 2021, a year after the first clinical trial participants received their shots.
Because it might be that we need boosters to rev up waning immunity over time, like with tetanus.
To cover the bases, Moderna is also working on a novel booster candidate against
new strains that have emerged since the initial vaccine was developed,
just to be sure our immune systems also recognize those.
But it’s also possible that the virus might continue to mutate in ways that make current
vaccines less effective, requiring a system more like the flu shot.
Yearly flu shots aren’t so much boosters as whole new vaccines.
In short, we’re going to need a lot more information before we know exactly how often we’re
going to need to be vaccinated against COVID-19 -- and how much those vaccines will need to change.
The good news is, scientists are on the case, so we won’t be left hanging forever.
Like I said earlier, immunology is complicated. But we’re getting better
against COVID-19 -- and all the other pathogens that cross our path.
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