No, the COVID-19 vaccine doesn't change your DNA. But it does make some long term changes. And that's a good thing.

Cartoon by: Maki Naro, from

One of the common tropes among anti-vaxxers lately is that the Covid-19 vaccine “changes your DNA.” Oh, the horrors!

Do they even know what they mean by that? Almost certainly not. Anti-vaxxers generally have no idea how biology works; often they are so confused that I’m tempted to say they are not even wrong. Even when they are right about something, it’s for the wrong reasons.

Many articles have already been posted explaining that the vaccine can’t alter your DNA, including a wildly popular piece at Forbes and explainers by the CDC and UNICEF.

So let’s dig into this strange notion that the vaccine changes your DNA. First, let’s look at what the CDC has to say:

“Will a COVID-19 vaccine alter my DNA? No. COVID-19 vaccines do not change or interact with your DNA in any way. Both mRNA and viral vector COVID-19 vaccines deliver instructions (genetic material) to our cells to start building protection against the virus that causes COVID-19. However, the material never enters the nucleus of the cell, which is where our DNA is kept.”

I see what they’re getting at here. They’re partly right, but in an attempt to give a simple “no” answer, the CDC got it wrong. It’s true that Covid-19 vaccines don’t directly alter your DNA, and it’s true that they don’t invade the cell nucleus, where your DNA resides. But that’s not the full story.

(The UNICEF article is more accurate and more nuanced, writing instead that “the information regarding harmful effects of the vaccine against COVID-19 on human DNA is unfounded and untrue.”)

Remember that the whole point of a vaccine is to prevent future infections. That means that something in your body has to change, right? So what is different?

Okay, take a deep breath and we’ll dive in. Whenever your body is invaded by a foreign cell–whether it’s a bacteria, a virus, a fungus, or some other pathogen–your immune system starts selecting from among millions of specialized proteins called antibodies, each one a little different. The way it does this is really rather extraordinary: many little pieces of your DNA are cut and pasted together, in millions of combinations, each making a different antibody. Eventually, one of these antibodies “recognizes” the pathogen (by binding to it).

What’s even more amazing is that the successful antibodies are “remembered” by the immune system, in the form of special cells called B-cells that have slightly different DNA! The DNA in these B-cells encodes just the right antibody to recognize the invader–the Covid-19 virus, that is. Once you recover from the infection, some of those immune cells (B-cells and T-cells–it's complicated) persist in your lymph nodes, constantly looking for any reappearance of the virus.

Or, as Ed Yong more colorfully explained:

“Picture the lymph nodes as bars full of grizzled T-cell mercenaries, each of which has just one type of target they’re prepared to fight. The messenger cell bursts in with a grainy photo, showing it to each mercenary in turn, asking: Is this your guy? When a match is found, the relevant merc arms up and clones itself into an entire battalion, which marches off to the airways.”

(For a deeper dive into how the immune system works, see Ed Yong’s feature article on this topic in The Atlantic from August 2020.)

The DNA in these special "memory B-cells is a little bit different from the DNA in all of your other cells. The vaccine itself doesn't stay around, but it "shows" the immune system a few copies of the spike protein from SARS-CoV-2, the Covid-19 virus, and the immune system remembers. And, I should note, a similar change to your DNA happens if you’re infected by the Covid-19 virus itself.

But B-cells are just a tiny, tiny portion of your body. Every other cell type, from skin to heart to lungs to brain, is completely unaffected by the vaccine. And if we didn’t have any way of “remembering” how to fight off infections, then we’d never become immune to anything, in which case the human race would quickly go extinct.

Finally, let me mention one other bit of misinformation. Early in the pandemic, some very well-known biologists at MIT published a paper claiming that the SARS-CoV-2 virus could, through an elaborate and highly implausible mechanism, integrate into the DNA of cells that were infected. This would indeed be worrisome! Many others quickly pointed out that this result could also be explained by more mundane mechanisms (experimental artifacts, essentially), and in the subsequent year and a half, with hundreds of millions of infections, no one has reported a single case where the virus actually did this. So not only is this event (reverse transcription of viral RNA into a human genome) really, really implausible, it also doesn’t even apply to vaccines, which only contain a small fragment of the viral mRNA.

(As an aside, that study by the MIT biologists was highly irresponsible. They were basically showing off their technical skills, saying “look what we can get the virus to do!” without considering how their work might be twisted, once anti-vaxxers got their hands on it. And the CDC response that I quoted above appears to be a direct response to misinterpretations of the MIT study.)

So back to our original question: does the Covid-19 vaccine change your DNA? Not directly, no. But yes, thanks to your own immune system, the overall mixture of DNA in your body is a tiny bit altered after you get any vaccine. Your DNA is also changed every time you recover from an infection, including the common cold. But the only change is in the DNA of a tiny number of immune cells, which hang around as guardians against future infections. And that’s a good thing.

The mRNA vaccines are defeating COVID. Let's use them for the flu.


The last year has been a story of triumph in the vaccine world, with the rapid development of two highly successful vaccines for Covid-19, one developed by Moderna and the other by Pfizer and BioNTech. Now that flu season is approaching, why are we still using 50-year-old technology for the flu vaccine?

The reason the Covid-19 vaccines were developed so quickly is that they used a new, much faster and easier-to-create type of vaccine technology, based on messenger RNA, or mRNA. What’s even more exciting is that we now have an overwhelming amount of evidence, from real-world experience, that these vaccines are remarkably safe and effective.

Now, anti-vaxxers and the “vaccine hesitant” are claiming they don’t trust the vaccine because it was developed too fast. That’s ridiculous: the real reason they don’t trust the vaccine is because they’re consuming a steady diet of anti-vaccine nonsense, promoted by a combination of right-wing media and the Disinformation Dozen (who include left-wing as well as right-wing zealots). But let’s not go down that rabbit hole today.

So what is an mRNA vaccine? Here’s a brief explainer, and then we’ll look at the flu vaccine. (Note: feel free to skip ahead if you already understand the technology.)

Messenger RNA vaccines have been under development for decades, since long before Covid-19 appeared. The technology required a series of breakthroughs over the years, as described in a recent Nature news story, and many scientists contributed. It wasn’t used in vaccines in part because it wasn’t ready, but also because we rely on private companies to develop vaccines, and few of them were interested in investing in a new, not-yet-approved technology. But I digress.

Messenger RNA is the stuff that all of your cells use to translate your genes, which are encoded in DNA, into proteins. The basic process is that the DNA for a gene is copied into pieces of mRNA, where the DNA letters, ACGT, are replaced by slightly different (chemically) RNA letters, ACGU.

Every cell in your body is filled with mRNA, all the time. It’s the stuff of life, so of course it is totally safe. Each cell uses mRNA to make proteins, which do most of the actual work that keeps you alive.

Here’s the brilliant thing about mRNA vaccines: all they do is introduce some mRNA into your cells that encodes a single protein from the virus, which is called “Spike” in the case of the Covid-19 vaccines.

Your own cells then make the Spike protein, but they don’t make very much! They just make a few copies, because mRNA doesn’t last very long. And because there is no DNA copy of the Spike protein in your genome, once the mRNA in the vaccine breaks down, it’s gone forever.

The other brilliant thing is that your own immune system recognizes Spike as a foreign protein, and it generates cells that will recognize any future infections where the Spike protein is present. If you’re later infected by SARS-CoV-2 (the Covid-19 virus), your immune system is primed and ready, and in a large majority of cases it attacks and destroys the virus before you get sick.

So that’s it: an mRNA vaccine is simply a little package made of fat molecules (called liposomes) that contains a few copies of mRNA encoding a viral protein. There’s nothing to prevent us now from creating similar vaccines for the flu, or for other viruses where we need new vaccines. (In the case of flu, we can use mRNA for a gene called hemagglutinin, but again I digress.)

We make new flu vaccines every year, because the flu is constantly mutating. Most years, the flu vaccine isn’t a great match for the circulating strains of the virus, and therefore the vaccine isn’t very effective. In a good year it might be 60-70% effective, but in bad years it might be much worse. A big part of the problem comes from how we create the vaccine.

In the U.S., we make most of our flu vaccines by growing influenza viruses in chicken eggs. No, I’m not making this up. Around February of each year, a panel of experts selects 4 strains of the virus that they think will most likely match the viruses for the following flu season, which usually ramps up in November or December. (Here are this year’s choices.)

Once the experts have selected the vaccine strains, the manufacturing process begins, first by checking to see if all 4 strains will grow robustly in chicken eggs. If they don’t, the panel may have to switch to different strains that are less likely to work. No, I’m not kidding: the success of the flu vaccine depends on how well it grows in eggs. That’s one reason why, in some years, the flu vaccine is a flop. This would simply never happen if we used mRNA technology.

With mRNA vaccines, we don’t have to grow any viruses at all. The mRNA from a single gene–hemagglutinin for influenza–can simply be synthesized in large quantities, just as we’re now doing for the Spike protein in SARS-CoV-2. Or for an even more effective vaccine, we might add the gene for neuraminidase, the other protein in influenza that our immune system can “see.”

An mRNA vaccine for flu would be far cheaper to manufacture, not requiring huge chicken farms. (This year, 82% of flu doses in the U.S. were made this way.) Even more important, though, is that an mRNA vaccine for flu would likely be far more effective at controlling the severity of the infection itself.

Why aren’t we doing this already? Simply put, it’s because we rely on private companies to take the initiative, and it’s not worth it to them to test and validate an entirely new vaccine, which requires a substantial investment. There’s also a simple solution, the same one we used for Covid-19: the government should take the lead.

We’re now at the beginning of flu season, which almost disappeared last year thanks to our social distancing and masking behavior. I’ve had my flu shot, and millions more are being administered around the world. Just last week, an early report out of Europe indicated that the flu season this year might be “severe,” which is the last thing we need with Covid-19 still raging.

We don’t yet know if this year’s flu shot will be effective or not, but odds are, based on past performance, that it won’t be great. (It’s still much better than nothing, I should add.) If we want a better flu vaccine, now is the time to start developing a new one using mRNA. If private industry doesn’t step up, any one of dozens of countries have the expertise to do so instead.

Sorry Tucker, ivermectin still doesn't work

Who knew that Tucker Carlson was a fan of science from Iran, Iraq, and Egypt? It turns out that much of the evidence supporting Tucker’s favorite Covid-19 treatment relies on deeply flawed studies from those countries.

But let me back up for a minute first.

I wasn’t planning to write about ivermectin again. Just two months ago, I explained in some detail that ivermectin simply doesn’t work. I also pointed out that prescriptions for ivermectin have exploded, largely due to relentless promotion of it by conservative media hosts including Tucker Carlson, Sean Hannity, and Laura Ingraham.

Official sources including the FDA and the CDC have been trying to explain that ivermectin is useless, but they have been far too timid, as I explained before, issuing press statements that, while clear enough to trained scientists, sound very wishy-washy to the general public.

So what’s new? Well, two new articles have appeared that explain a bit more about where all the confusion comes from. The first is a scientific paper, still in preprint form (not yet peer-reviewed), by the scientists who published one of the recent studies that initially reported positive results about ivermectin.

In their preprint, Andrew Hill, Manya Mirchandani, and Victoria Pilkington re-analyze the studies that went into their recent meta-analysis–which, I should add, they have already retracted. Let’s look at their new analysis.

In their original study–one that promoters of ivermectin often cite in support of their arguments–Hill and colleagues looked at data from 24 different studies of ivermectin, and concluded that, on average, it did seem to reduce mortality from Covid-19.

But then they found that some of these studies were fraudulent, and others were so heavily biased that they didn’t trust their own findings. They retracted their own study just a month after it was published. Kudos to them!

Now they’ve gone even further. They went back and re-graded those 24 studies based on how biased or otherwise flawed they were. Their new report explains that there’s a very strong correlation between the amount of bias and the apparent benefits of ivermectin. In other words, the more biased the study, the greater the benefit. When they excluded the biased studies, the benefits simply disappeared.

In other words, the data from the high-quality studies show that ivermectin doesn’t work.

The lowest-quality studies were conducted in Iran, Turkey, and Iraq, and the worst of all were two potentially fraudulent studies out of Egypt and Lebanon. (In the Egyptian study, it was revealed that “79 participants were duplicates, some deaths were recorded on dates before the trial had started and instances of plagiarism were identified in the text.”)

So apparently Tucker Carlson, Fox News’s biggest promoter of ivermectin, prefers studies from Iran, Iraq, Egypt, and Lebanon over much higher-quality studies out of, for example, Colombia (Lopez-Medina et al., published in JAMA), India (Ravikirti et al.) or Brazil (Bermejo Galan et al.).

But why the heck is anyone getting medical advice from Tucker Carlson?

The second new article appeared in The Atlantic last week, written by James Heathers, a data scientist who has uncovered flaws in multiple studies of ivermectin. Heathers’ summary of the problems is terrific, and I highly recommend that readers check it out, but I’ll share a few tidbits here.

Heathers describes the process of digging into the details of these studies, which is difficult and thankless. He’s not paid to do this; he’s just a good scientist who cares about the integrity of the literature, and it obviously bothers him when he sees shoddy science that has passed through peer review. “We do it because we feel it should be done,” he writes.

One of his main points is that bad studies get published all the time, and they simply remain out there, because who has time to go through all of them? Most of them don’t matter, and they are quickly forgotten.

In the case of ivermectin, Heathers found flaws in study after study. More tellingly, he observed the same phenomenon that Hill, Mirchandani, and Pilkington found: the biggest benefits of ivermectin appeared in the worst studies. As Heathers explains:

“the studies we are certain are unreliable happen to be the same ones that show ivermectin as most effective.”

Why did this happen with ivermectin? In retrospect, it’s not surprising: some doctors and scientists really wanted it to work, they let that bias creep into their studies. Maybe they ignored the patients who got sicker after ivermectin treatment, or maybe they made sure the sicker-looking patients got the placebo. (These would be big red flags if they happened.) Or maybe they had outside motivations–political pressure, for instance–to produce a positive study about ivermectin.

The peer-review process is supposed to catch these problems, and it’s slowly catching up now, as reflected in the new review from Hill et al. But as Heathers points out,

“Publishing science is slow; highly contagious diseases are fast.”

Meanwhile, the data pretty clearly show that ivermectin is useless against Covid-19. We desperately need effective treatments, and we should stop looking up this blind alley.

Before concluding, I’d be remiss if I didn’t point out (again) that ivermectin is a genuine drug, used to treat infections by two parasites: a nematode called Onchocerca volvulus that causes river blindness, and an intestinal nematode called Strongyloides stercoralis. It’s highly effective against these nematodes, which are sometimes called worms because they are worm-shaped, even though they are microscopic.

Unfortunately, people continue to take ivermectin, so let me say it again here: ivermectin does not work. It doesn’t treat Covid-19, it doesn’t prevent Covid-19, and it doesn’t reduce your risk of severe illness from Covid-19.

Oh, and one more thing: if you’re looking for medical advice, don’t get it from Tucker Carlson.