Vaccines: Pregnancy and Lactation Edition

For readers of this newsletter, one of the most prominent questions that has come up about the COVID-19 vaccine is whether it is safe for pregnant people, those who are breastfeeding and those who plan to conceive. Even for people who would have no hesitation being vaccinated if not pregnant have mentioned thinking twice about it.

Today, I want to run through what we know, what we don’t, when we might know more. I won’t be able to give you the definitive answer you want if you’re pregnant (breastfeeding/conceiving is easier), but my hope is — like always — I can help you think about it. (Thanks to Nathan Fox, also, who helped me think through these issues).

(Note: I talked about the general underlying science of mRNA vaccines a couple of weeks ago. I wont revisit that all here, but you can look back to this post.)

What Do Official Messages Say?

Official messages around this issue vary. The Emergency Use Authorization for the mRNA vaccines in the US suggests that pregnant and lactating people should be eligible to get them. This is the official word, and it means that for pregnant people in the US, the vaccine is available (if they are in a group which would otherwise be eligible — at this point, front-line health care workers). Organizations like ACOG have also suggested vaccination of pregnant people is a good idea. Generally, the messaging in the US has been mostly positive, if cautious.

In the UK, the vaccine approval currently does not include pregnant people. The UK has taken the view (expressed here in Scotland’s decision) that without detailed information on safety, they are not comfortable with this group being vaccinated.

What Does the Science Say?

The reason this is happening, at the core, is that pregnant and lactating people were not included in vaccine trials. The reason for this is that we are generally hyper cautious with “experimenting” on pregnant people. Other vaccine trials or drug trials typically do not include this group in the first wave. There are ethical reasons to exclude these groups since they may be higher risk, although some have argued that it’s unethical to exclude these groups. Anyway, they’ve been excluded.

What this means — and this is the underlying source of the caution/concern — is that we have no systematic data on these vaccines in pregnant people.

This doesn’t mean, however, that we know nothing. Even if we do not have data on this particular vaccine in pregnancy, we have lots of data in general on vaccination in pregnancy. And, in general, inactivated or killed virus vaccines (of which the COVID-19 vaccines are an example) are considered safe to use in pregnancy. Every year, pregnant people get the flu vaccine, which is a killed virus vaccine. Every year this vaccine is new (i.e. targeting a new flu strain) and we have no concerns about vaccinating pregnant people with it.

More caution is used with live virus vaccines, which are generally not recommended during pregnancy. This includes, notably, the chicken pox vaccine. The worry is that with a live virus vaccine, even a mild form of the virus might have a bad effect on the fetus. A fetus can be harmed by mom getting chicken pox during pregnancy; there is a worry that a similar harm could be generated by the live virus vaccine. It should be noted that this concern is largely theoretical. In small samples of women who have gotten the chicken pox vaccine during pregnancy, there doesn’t seem to be evidence of harm.

However: regardless of how you feel about the appropriateness of live virus vaccines in pregnancy, the COVID-19 vaccines are not in this category. They are mRNA vaccines, meaning they contain RNA fragments which get your cells to produce a particular viral spike protein. There is simply no reason they would pose a problem in pregnancy.

This is more true, even, for breastfeeding people and those trying to conceive. There is just no reason to think there would be problem with safety of these vaccines during these periods.

This is, of course, different from saying that we know they are safe. We have not done safety trials, as noted, since pregnant people were not in the vaccine trials. Bottom line: all of the evidence suggests these would be safe, but we cannot say for sure.

Why is the Messaging So Confusing?

My sense is we all agree on the basic facts — lots of reason to think this is safe, no certainty — and the difference across advice is in how this is interpreted. As I reflected on this, I think a big issue is that this situation is so unique.

Most of the time, when we produce a new vaccine, it is not for a virus that is posing an immediate threat to prime age adults right now. This is because mostly we do not have viral pandemics, and vaccines take time to develop. For the most part, we do not find ourselves in a situation where vaccines are needed to prevent disease right now.

This means that most of the time there is somewhat less urgency to be vaccinated. And in that case, it makes sense for vulnerable populations like pregnant people to wait to be vaccinated until we know more about safety. This is how we are used to thinking about vaccines and pregnancy: there is no immediate disease threat, so no strong reason to vaccinate right now, so better to wait for more certainty.

This does not describe our current situation.

COVID-19 is around now. It is dangerous. Even though most pregnant people will not have serious illness, this group is at risk, probably slightly higher risk than the general population. Fully isolating to avoid the virus also carries risks — mental and physical health risks, economic risks, etc. This means that there are very, very good reasons to vaccinate pregnant people now, even if we cannot yet be sure about safety.

My sense is the messaging is confusing precisely because it has relics of the status quo. It’s hard to switch our thinking to the current moment.

What Should I do?

Let’s get to the real question. If you are pregnant or breastfeeding, and you’re being offered the vaccine, should you get it? The US guidance means you can, although they suggest you speak to your doctor about the benefits and risks. This flexibility is good in some ways, although I think has left many people feeling like they’re making decision in the dark.

Really, it comes down in the end to weighing benefits and risks. This is simplest for people who are breastfeeding or planning to conceive. There is simply no reason to think the vaccine would pose a special risks to these groups. There is even some possibility of antibody protection for infants for breastfeeding people (this is hypothetical at this point). There are big benefits to the vaccine.

For pregnant people the choice may be (very slightly) more complicated.

I thought this decision tool was extremely helpful.

In my view, the key thing to recognize is that getting COVID-19 is much riskier than getting the vaccine. Yes, we cannot rule out some long term risk of the vaccine (although there is no reason to expect there would be one) but we similarly cannot rule out long term risks from COVID-19. And we know COVID-19 infection has short term risks.

Of course, you may not get COVID-19 and the vaccine is a certainty if you get it. One way to think about it: If you are in a situation in which it is easy to totally avoid COVID-19 risk, then that’s one thing and, in that situation, it may be reasonable to wait. This is not likely to be true for many of the front line health care workers who are first in line, but it may be true as more people are eligible for vaccination.

When Will We Know More? (And a Call to Action!)

Safety trials for pregnant people and children are likely to start in the New Year, but they take time, and it will be some time until we have safety data. However, we are likely to start to learn a bit more even before that data is in. For one thing, there are some people who were pregnant in the existing trials but didn’t know it — they provide a small amount of data.

We will also start to learn from some of the amazing front line health care workers who are pregnant and got vaccinated (shout out to Jenn K here!). This isn’t a systematic randomized sample, but in this era of COVID-19 we should learn where we can. Keeping track of any adverse events and outcomes for vaccinated pregnant health care workers and their babies — will give some sense of possible risks. My sense is we’ll know more in a month than we do now, and knowledge will keep growing.

Call to Action. Edited to Add: A number of you have asked me about whether I know of anyone who is tracking pregnant or lactating people who are vaccinated. Yes! There is a registry for pregnant and lactating people who have been vaccinated here.

Will be thinking of you all this week; I hope you find some rest in the holiday, and let’s hope for better things in 2021.


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Keep the thoughts coming. I’m going to be slow over the holidays, so I will probably write less than usual, but I do read your emails so please keep the ideas coming.

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