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
gene.com/stories/the-antibody

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.

A new kind of fasting provides significant immune system benefits

I've written about fasting and its effects on health before. Six years ago, a study showed that a 3-day fast can essentially reset the immune system, providing many potential benefits. These benefits include better cardiovascular health, better endurance, lower blood pressure, and reduced inflammation.

Newer data, which I'll get to in a minute, shows that you might not have to fast nearly that long to get these benefits.

In the 2014 study, Valter Longo and colleagues at USC found that fasting lowered white blood cell counts, which in turn triggered the immune system to start producing new white blood cells. White blood cells (or lymphocytes) are a key component of your body’s immune system. Once you start eating again, according to Longo, your stem cells kick back into high gear to replenish the cells that were recycled.

The idea behind this strategy is that you have to fast for several days to get the benefits: basically, you have to fully deplete your energy reserves (in the form of glycogen), and it takes your body at least 24 hours, and probably 48 hours or more, to do this. That's the not-so-good news. The good news is that you probably only need to fast once or twice a year to gain the benefits that Longo described.

Last week, in a paper just published in the New England Journal of Medicine, Rafael de Cabo and Mark Mattson reviewed multiple strategies for fasting that have been tested in the years since Longo's study. The news continues to be very encouraging: intermittent fasting is good for you. I don't have time or space here to discuss all the results, but I want to focus on one fasting strategy that has surprisingly good benefits.

It turns out that you can get many of the benefits of fasting without doing a 3-day fast, which for most people is really, really difficult to accomplish. Instead, you can try a much easier type of fasting, called "time-restricted" fasting. With this strategy, you fast every day, by eating all of your food in a 6-hour or 8-hour window. Or you can go with the more difficult strategy (but still easier than a 3-day fast) where you fast for 2 entire days per week. Here, then, are two intermittent fasting strategies that have similar health benefits:

• Time-restricted: eat lunch starting at 12 noon, and finish dinner by 8:00pm. Fast until the next day at noon (16 hour fast). Do this every day.
• 5:2 fasting: fast for 2 different days each week, which means eating just 500-700 calories worth of food and drink on those days. Eat normally on the other 5 days.

The first strategy–a daily 16-hour fast–is the easiest, but its benefits might be equal to those of 5:2 fasting and the 3-day fast. (No study has directly compared these 3 fasting regimens.)

The benefits of intermittent fasting are numerous. As de Cabo and Mattson explain, they include

"[improvements in] blood pressure; resting heart rate; levels of HDL and LDL cholesterol, triglycerides, glucose, and insulin resistance.... In addition, intermittent fasting reduces markers of systemic inflammation and oxidative stress that are associated with atherosclerosis."

Fasting also helps with weight loss, for obvious reasons. Cutting out all snacks in the evening, which is the biggest change imposed by time-restricted fasting, means not only a reduction in calories consumed, but also a reduction in the amount of highly processed ("junk") foods in one's diet as well.

Furthermore, because intermittent fasting reduces inflammation, it may also improve symptoms of arthritis and even rheumatoid arthritis.

Why does fasting work? It's all about getting your body to switch over from glucose metabolism to ketone metabolism. Our usual 3-meal-a-day diet provides our body with a constant source of fuel in the form of glucose. Once that glucose is used up, though, our body switches to using fatty acids and ketone bodies. Ketone bodies provide more than fuel: as de Cabo and Mattson explain,

"Ketone bodies regulate the expression and activity of many proteins and molecules that are known to influence health and aging."

Ketone metabolism seems to bring a host of health benefits. The trick is getting our bodies to switch over to it, now and then. If we eat constantly, then our bodies happily subsist on glucose and never make the switch.

Does fasting truly reset your immune system? Six years ago, I concluded that a 3-day fast does the trick, at least partially. The science suggests that, if you can do it, a prolonged fast for 2-3 days will induce your body to clean out some old immune cells and switch on production of new ones. Now we're learning that intermittent fasting, which is easier to do, may work in much the same way, with multiple health benefits.

[Note: one of the authors of the NEJM study, Mark Mattson, is a Professor at Johns Hopkins School of Medicine, making him a colleague of mine. However, we are in different departments and we have never met.]

Sniffle. It's allergy season again. Do those shots work?

Ah, spring is in the air. The flowers are blooming and the trees are bursting into leaf.

For many of us, this time of year means one thing: allergies. The price of going outside for any length of time is sneezing and itchy eyes that last for many hours, even after we return indoors. Rather than going out and enjoying the warm air and colorful vegetation, we close the doors and windows and stock up on antihistamines and eye drops. Studies show that 20–40% of people in the U.S. have allergies.

Your local pharmacy has shelf after shelf of allergy treatments, ranging from mildly effective (Zyrtec and its equivalents) to laughably ineffective (anything homeopathic). But even the best pills have side effects, and they only serve to suppress the symptoms. As one study put it:

"Patients struggle to alleviate their misery, frequently self-adjusting their treatment regimen of over-the-counter and prescription medications because of lack of efficacy, deterioration of efficacy, lack of 24-hour relief, and bothersome side effects."

Isn't there a way to tell your body to just stop it already? After all, pollen is not a pathogen. Our misery is caused by our own immune system's over-reaction: it ramps up in response to the foreign particles (pollen) in our eyes and airways and creates a histamine reaction, which is simply not necessary.

None of the over-the-counter pills prevent this reaction, but they can dampen it–hence the term "antihistamine." However, what if there were a way to tell your body to simply chill out and ignore the pollen?

Well, maybe. You can get allergy shots. This is a surprisingly simple procedure: your doctor takes a small, diluted amount of the allergen (pollen, cat dander, etc.) and injects it into your arm. Over the course of many months, your doctor will very gradually increase the amount being injected. You have to go for the shots every week, and continue them for several years.

The question is, do they work? The answer is a qualified yes.

NIH and the Agency for Healthcare Research and Quality (AHRQ) have put together a long explainer of the evidence for and against allergy shots, which you can find at PubMed Health. The NIH study looked at 74 clinical studies of allergy shots. To save you some time, I'll cut to the chase: the evidence is quite good that shots work. Or, as the AHRQ study put it,

"we found high grade evidence that subcutaneous immunotherapy reduces rhinitis/rhinoconjunctivitis symptoms."

This might seem like pseudoscience, but it's not: what's happening is that your immune system is being de-sensitized to the allergen. It doesn't work for everyone, but in many people, this gradual de-sensitization trains their immune system not to react so badly. It's not necessarily permanent, either: after stopping the shots, allergies might re-appear after a few years.

So if you're looking out your window at the beautiful spring weather with a box of tissues by your side, maybe you have a way out. Talk to your doctor or visit the AAAAI site to find an allergy specialist. Don't expect miracles or a quick fix, but allergy shots are the best we've got, for now.

Does a 3-day fast reset your immune system?

I’ve been hearing new reports lately that sound an awful lot like pseudoscience: that fasting for an extended time, two days or longer, can reset your immune system and provide other health benefits. I first heard about this when a friend and colleague at Stanford University announced he was going on a 3-day fast. To explain, he pointed to a recent study, which I’ve now read.

Diet advice, including fasting-based diets, can be found all over the Internet, and much of it is nonsense, so I was very skeptical about these latest claims.

This time, though, there might be something to it. The scientific study that my colleague told me about was published back in June by USC’s Valter Longo, who studies aging and longevity. In this paper, Longo and colleagues described remarkable metabolic changes that occurred as a result of prolonged fasting. They found that fasting for 3 days or longer–drinking only water and eating less than 200 calories per day–can truly “reset” some components of your immune system. 

The research looked at both mice and humans. (It’s far easier to run the experiments in mice, of course, but we can’t always trust that the same effects will occur in humans.) In both species, fasting lowered white blood cell counts, which in turn triggered the immune system to start producing new white blood cells. White blood cells (or lymphocytes) are a key component of your body’s immune system.

Longo’s hypothesis is that fasting (or starvation) forces your body to “recycle a lot of the immune cells that are not needed” which explains the drop in the white blood cell count. Two of the key mechanisms are an enzyme called PKA and a hormone called IGF-1, both of which are reduced by fasting. Once you start eating again, your stem cells kick back into high gear to replenish the cells that were recycled.

The human part of the study was much more limited: a group of cancer patients fasted for 1, 2, or 3 days prior to chemotherapy. The idea is that fasting might reduce the harmful side effects of chemotherapy, particularly the immunosuppression caused by some chemotherapeutic drugs. These results are very preliminary: the patients are participating in a phase I clinical trial, which is designed to assess safety, not effectiveness. Nonetheless, the results indicate that a 3-day fast (but not a 1-day fast) was beneficial for these patients.

A key finding in this research is that you have to fast for several days to get any benefit: basically, you have to fully deplete your energy reserves (in the form of glycogen), and it takes your body at least 24 hours, and probably 48 hours or more, to do this. This is much harder than a 1-day fast, which many people do routinely. 

On the other hand, Valter Longo has compared the effects of periodic fasting to long-term caloric restriction, which has been shown to prolong lifespan in mouse and other animals. In a separate review article, Longo wrote: 

“Fasting has the potential to delay aging and help prevent and treat diseases while minimizing the side effects caused by chronic dietary interventions.”

Caloric restriction is extremely difficult to achieve for humans: you have to nearly starve yourself for years. Compared to this, an occasional 3-day fast should be a snap.

Caveats: fasting can be harmful, especially for people who have other health problems. If you’re seriously thinking of trying this, you should consult your doctor first. And this preliminary evidence, though encouraging, is primarily based on mice, not people. We might eventually learn that the benefits of fasting are outweighed by other problems. Fasting for more than two days isn’t easy, either: you’re going to get really hungry. 

Does a 3-day fast truly reset your immune system? Well, maybe not a total reset, but at least a mild refresh. The science suggests that, if you can do it, a prolonged fast for 2-3 days or longer may induce your body to clean out some old immune cells and switch on production of new ones. Stay tuned.

[An interesting aside: this study was lengthy and complex, and the authors apparently went to great lengths to satisfy the peer reviewers: the paper was submitted in October 2012, re-submitted after revision in December 2013, and finally accepted in April 2014. 18 months is a very long time.]