There was a time — let’s say, 2019 — when people did not talk as much about vaccines. It’s not that they never came up, but COVID has made vaccination more visible and more controversial than it once was.
We are now roughly on the other side of the pandemic at some new vaccine normal. But the level of interest and discussion hasn’t returned to baseline — my casual analysis of Google Trends suggests that interest in the term “vaccine” is about four times higher this week than in the corresponding week in 2019. People are talking more about vaccination, thinking more about it, and weighing more options.
Adding to this: the landscape of seasonal vaccination has changed. In 2019, there was a flu vaccine. Flu is still here, but it’s been joined by COVID and, for some, by the option for an RSV vaccine. I’ve been getting a lot of questions on these — which to have, when, who, etc., etc. It’s time to do some explaining.
Today’s post is in four parts, and we’ll link here so you can skip down to the part you want.
- How do vaccines work? A (very) brief explainer
- The seasonal vaccine landscape in 2023: flu, COVID, RSV
- Vaccines in pregnancy
- Routine childhood vaccinations
Part One
How do vaccines work?
To understand how vaccines work, it’s useful to start with viruses; in particular, with what happens when you become infected with a virus.
In broad terms: viral exposure prompts action from the immune system.
Your immune system has many parts. Some of them are general, designed to ward off any pathogen (for example, your nose hair). Some of the components are targeted. When you become infected with a particular virus, cells of the immune system are engaged to create antibodies to the antigen (the virus cells). These antibodies are designed to latch onto the antigens and destroy them. As your body makes more and more antibodies, they (hopefully, in most cases) overwhelm the antigens and neutralize the virus. Along the way, you may feel ill, but as your antibodies win, you’ll start to feel better.
Once you are better, the antibodies stick around in your system for a while. The value of this is that if you encounter the virus again in the short term, you’re ready for it and you can fight it off quickly (and likely not be sick at all). Over time, antibodies fade but your body retains memory T cells, which remember how to make the antibodies. This means that the next time you encounter the virus, even if it is after the antibody-retention period, your body is ready to fight more quickly. This is why the second (or later) time you encounter a virus, you’ll generally either not get sick or get less sick.
Vaccines work by mimicking the virus, prompting the production of antibodies and memory T cells, but without making you sick. The result is an immune system that is ready if it encounters the virus in the wild, but without the initial need to be exposed to the illness.
There are a number of different ways a vaccine can do this. The most common traditional vaccines are made with inactivated viruses. Flu vaccines, for example: the virus is grown in chicken eggs, treated with a chemical to kill it — so it cannot make you sick — and used in the vaccine. Even though the virus is dead, it has the same structure, and your body recognizes it as an invader and produces antibodies to it.
Most COVID-19 vaccines are mRNA vaccines (m = messenger). These vaccines work slightly differently. Rather than containing a killed form of the virus, the vaccine contains instructions for your own cells to produce a single protein from the virus (in the case of COVID-19, the spike protein). When you get the COVID-19 vaccine, some of your cells get instructions to produce this protein. They produce the protein, and your body recognizes it as foreign. You create antibodies to the protein, which also serve as antibodies to the virus. If you encounter the COVID-19 virus in the wild, then you’ve got the antibodies ready.
(There are a couple other ways to make vaccines, but these are the primary approaches for the vaccines we commonly use.)
Regardless of mechanism, the basic idea is the same: find a way for your body to create antibodies to the virus without actually becoming sick from the virus. Once you do that, you’re good to go.
Variation in efficacy
Before moving to specific vaccines, a quick comment on variation in efficacy. There are some vaccines — the childhood measles vaccine is a classic example — that are incredibly effective. A child who is fully vaccinated for measles is not only extremely unlikely to get measles — like, extremely unlikely — but is also extremely unlikely to spread measles. This is because the immunity delivered by the measles vaccine is extremely durable and the vaccine generally delivers what is called sterilizing immunity. Basically, the length of time the pathogen takes to replicate is sufficiently long that the immune system response is faster, and it never really gets going. The transmission of measles is therefore cut off.
There are other vaccines, like the seasonal flu vaccine, where the effectiveness is lower. One reason for this is that there is some guesswork in making the flu vaccine, and depending on how close the match of the vaccine is to the circulating form of the virus, efficacy may be more or less. It’s nearly always the case that a flu vaccine lowers the risk of getting the flu and makes it less severe if you do get it, but it doesn’t always fully protect you.
With this background, let’s move to some specifics.
Part Two
The seasonal vaccine landscape in 2023 — flu, COVID, RSV
Before the pandemic, there was one seasonal fall vaccine: flu. During the pandemic, the COVID-19 vaccine was introduced — at first whenever available, but increasingly now moving to a seasonal schedule. This year, immunization from RSV (vaccines for adults; a related immunization product for babies) was introduced.
Should you get all of them? Who should get them?
Flu
Seasonal influenza kills a large number of Americans every year — the CDC provides estimates in the 15,000 to 50,000 range. Mortality from the flu is highest in infants and (especially) older people. School-age children are the group most likely to be sickened by flu, though, since schools are locations of high flu risk.
The seasonal flu vaccine is an effective method for lowering illness risk. There are a few ways to see this in the data, but my favorite work is by my friend Dr. Bapu Jena, who has a study in which he shows that kids with summer birthdays are less likely to be vaccinated for the flu than those with fall birthdays, because of the timing of their well child visits. The fall-birthday children are, in turn, less likely to get the flu and less likely to spread the flu to elderly family members.
Flu vaccines can lower illness risk for adults as well. For older adults, a flu vaccine is especially crucial, since flu is a major source of mortality. The good news is that side effects from flu vaccines tend to be quite mild.
The optimal time to get the flu vaccine, assuming a normal flu season timing, is around mid-October. (This is also based on Bapu’s research, and on the logic of how long antibodies last.) This provides maximum protection through a February flu surge. (The flu season has moved a bit earlier in the past few years, so I can also see a case for doing this now.)
Bottom line: Everyone should get this vaccine, ideally in mid-October.
COVID
At this point, it is appropriate to think about the COVID-19 vaccine updates as similar to the flu vaccine. Like the flu vaccine, the COVID vaccine will be reformulated every year to match circulating variants. We should expect a new vaccine — we can call it a booster, but I’m not sure that language helps — every fall.
The COVID vaccine will lower the risk of serious illness and hospitalization. We also expect it to have a small and short-lived impact on the risk of any illness. The size of this impact is unclear, partly just due to the limited data we have so far. The impacts on outward transmission are likely very small.
An important distinction between COVID and the flu is the age profile of risk. COVID has a much stronger age skew than the flu. The risk of serious illness and hospitalization for younger people is very low; this is especially true for children. When the primary value of the vaccine is to lower the risk of serious illness, the value of vaccination is much lower for this group than for older adults.
The CDC has recommended the seasonal COVID-19 vaccine for everyone over six months. This is in contrast to (for example) the U.K., which has focused on vaccination for older adults and younger adults with comorbidities. There are arguments for both approaches, and there is disagreement even within the U.S. about the appropriateness of this universal recommendation.
From an individual perspective: if you’re over 65, or you’re under 65 and you are at higher risk (due to other illnesses, being pregnant, or having a larger body), you should get the vaccine. If you’ve got older parents, encourage them to get it. A higher uptake in older adults will save lives.
If you’re a healthy adult, or you’re thinking about this for your children, the value is lower. Certainly, reasonable people will choose to get vaccinated in this group, and other reasonable people will not. For example: within my household, one adult is planning to get the shot and one is not.
One note: If you’ve had COVID within the past couple of months, there is no need to get this vaccine.
Bottom line: Older adults, or younger adults with immunocompromise (including pregnant women) should definitely get this vaccine unless they have recently had COVID.
RSV
RSV vaccines are the newest of these three, and I’ve written extensively about them in recent weeks, so I do not want to fully rehash this. You can read about vaccines for older adults here, and about the monoclonal antibody for infants here. An important note is that this shot for infants is not a vaccine; it actually delivers the RSV antibodies directly.
The clearest-cut recommendation here is for older adults, where the RSV vaccine has been shown to effectively lower mortality. The second clearest indication is for infants, where the monoclonal antibody (sold under the name Beyfortus) has been shown to lower hospitalization risk. The vaccine can be given at birth, and is approved for neonates and infants entering their first RSV season (so, those under nine months or so). It can also be given to children up to 24 months who are at higher RSV risk. The efficacy data is really impressive, and pediatricians are excited. A note is that this is not universally available yet, but keep asking!
There is also an approved vaccine for pregnant women that would provide some protection for their infants. The approval for this was more complex because of some worries in the trials about preterm birth. Whether to take this during pregnancy is something to discuss with your doctor.
Bottom line: Older adults should get this vaccine. Infants should get the monoclonal antibody if available. Pregnant people should discuss with their doctor.
Part Three
Vaccines in pregnancy
There are two reasons to get vaccines during pregnancy. The first is that pregnancy is a form of mild immunocompromise, so there is added value to vaccination for things that might make you sick. For example: both seasonal flu and COVID vaccines are recommended more strongly for pregnant women than for non-pregnant women of similar ages.
The second reason to get vaccinated is to pass antibodies on to your infant, which will protect them in the early weeks or months of life, before they can be vaccinated themselves. Both the Tdap vaccine and the new RSV vaccine are examples of vaccines that are geared toward infant protection, not mom protection. Non-elderly adults are not at high risk from either pertussis or RSV, so the only reason for these vaccines is the protection of the infant.
An important question about vaccination in pregnancy is timing. For infant protection, the ideal timing for vaccination is in the early part of the third trimester. This is enough time for antibodies to develop, but also close enough to the end that they are retained for several months post-birth. For the vaccines (Tdap and RSV) that are focused on infant protection, this is the optimal timing.
For the COVID and (especially) flu vaccine, there is a competing factor, which is protection of the mother. Flu can be quite serious in pregnant women, so there is an argument for vaccinating early to protect the mom. The value for the infant is also there, so the timing is not obvious. This is something that’s worth discussing with your doctor, and depends both on the exact timing of birth around the flu and COVID season and on your individual risk factors.
Part Four
Routine childhood vaccinations
Routine childhood vaccinations: pertussis, hepatitis B, measles. The ones that have been standard, in many cases, for decades. They’ve saved literally thousands, perhaps millions, of lives. And, yes, they still make some people nervous.
When I wrote Cribsheet, I spent many, many weeks researching vaccines and vaccine resistance. It’s a topic I’ve written on in my academic work, and it’s something I care a lot about. This isn’t the place to revisit that discussion, although if you’re feeling vaccine-anxious about routine childhood vaccination, I urge you to read that chapter of the book.
The bottom line — there and here — is that these vaccines have been widely tested and subject to scrutiny that is far outside of virtually any other medical intervention, and they’ve come out well. They’re safe, and although the diseases they protect from are rare, we do see deaths from pertussis in infants every year, and routine measles outbreaks in undervaccinated populations.
Please: get the routine vaccinations, even if they are the only ones on this list you get.
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Can you comment about studies that link the RSV vaccine and preterm birth? Many thanks.