What Fall Vaccines Should We Get?

The fall brings many things — the start of school, cooler weather, pumpkins … and also illnesses. If you have a school-age child, they’re probably bringing illness home along with their macaroni necklaces and math tests. And even if your child isn’t making a transition to school, the fall is still the time when respiratory viruses pick up. 

We’re going to focus on the big three: RSV, the seasonal flu, and COVID. To set the stage, the pictures below show the time path, by age, of hospitalizations for these three viruses in the past 12 months (these data come from the CDC). From these, we can see a few things:

• It’s clear why we talk about these viruses now — there is a big spike in the late fall and winter in illness.
• The age path of the viruses differs a bit. All three show much higher illness rates for older adults. For RSV, there is also a large impact on the youngest children. The flu also shows a large impact on the child age groups; COVID has less impact on younger people. 
• Finally, we have seen a summer COVID spike that is not there in the others. Flu and RSV are generally reliable winter viruses; COVID is somewhat less predictable.

The landscape of vaccines is particularly confusing right now, given conflicting information from health institutions. Generally, when in doubt, I’d recommend talking to your doctor directly. 

With this as background, we can turn to approaches to protecting yourself from these viruses this season.

RSV

I’m starting with RSV here for two reasons. First, of these viruses, it’s the one that disproportionately impacts infants. Second, the immunization options are newer, so there are more updates.

Most people will get RSV many times in their lives. For older children and healthy adults, it tends to manifest as a mild cold. The heavily affected groups are infants and older people. The goal of RSV immunization, therefore, is to protect these groups. I’m going to focus here on infants, but I will note that there is a vaccine for older adults for RSV that rolled out in 2023 and that is highly recommended for adults over 65 (this vaccine is not annual — it is given once).

In the case of infants, the focus is on protecting them in their first RSV season — that is, their first year of life. For healthy children, RSV infection at older ages may make them sick, but is very unlikely to result in hospitalization or death. For young infants, those are both possibilities.  

There are two great options for protecting infants in their first RSV season. The first is to give protection to the infant directly. In 2023, the FDA approved an immunization called Beyfortus for infants in their first RSV season. This isn’t a vaccine; it’s a monoclonal antibody. The core idea is that the shot delivers antibodies directly, unlike a vaccine, which induces the body to produce its own antibodies. 

In randomized trials run before approval, the immunization provided extremely good protection against RSV (about an 80% reduction in hospitalization and a 90% reduction in hospitalization with a need for oxygen). Within the past year, we’ve also started to get data from the real world on protection. Some of this comes from smaller studies run in the U.S., but I think the best evidence comes out of Spain. This study, published in The Lancet, compared RSV rates in 2023 — after widespread immunization — with prior years. It found almost a 70% reduction in the risk of RSV hospitalization and an almost 90% reduction in the need for supportive oxygen. These numbers are not surprising given the success in randomized trials, but it’s very helpful to see this in the real world (and to see that there were no significant adverse events). 

The other option for protection against RSV is vaccination during pregnancy. This approach uses another vaccine approved in 2023, Abrysvo, which is approved for use in pregnancy and for older adults. This option is a true vaccine — it induces an internal immune response. In pregnancy, it is given between 32 and 36 weeks, which gives time for antibodies to develop, pass to the infant, and then persist through the first months of life.

The initial data from vaccine trials showed that this option was also very effective in preventing disease in infants: 82% efficacy over the first three months of life. 

In the first approvals, there was a concern that RSV vaccination in pregnancy might increase the risk of preterm birth, based on the observation that the preterm birth rate was about one percentage point higher in the group that was vaccinated. Initial data from the real world, however, is more reassuring. This study, published in July 2024, uses data from New York State to compare preterm birth rates for women who had evidence of RSV vaccination during pregnancy with those who did not. The researchers found no signal of a higher preterm birth rate in the vaccinated group (the rates were actually lower, but not significantly so). 

Conclusion: Both immunization of infants after birth and vaccination during pregnancy are safe and effective approaches to RSV. The vaccine in pregnancy is a great option if you are due sometime in the fall because your infant will then be born with protection during RSV season. If your infant was born in the spring or summer, you’ll likely want to give them the immunization in the fall to get the timing right. If you had a spring baby and had the vaccine during pregnancy, you may also be able to get your infant Beyfortus; ask your doctor.

Seasonal flu

The seasonal flu kills an estimated 20,000 to 50,000 Americans a year, mostly older adults. Flu strains vary over time, so each year, there is a new seasonal flu vaccine, targeted to the current strain. The decision about which strain of flu to target is made in the spring, usually based on what strain is prevalent in the Southern Hemisphere at that time. The match of the vaccine to the flu strain varies over time, so efficacy varies. However, even if the vaccine isn’t perfectly matched to that year’s virus, it still provides some protection against serious illness.

Kids can get this vaccine starting at 6 months. In the first flu season, babies need two doses. After that, it is one dose each flu season.

From a parental standpoint, I think we learn the most about the flu vaccine from the work of Dr. Anupam (Bapu) Jena, Harvard researcher and co-author of Random Acts of Medicine. What’s very helpful about his research work is that Dr. Jena exploits a source of randomness in flu vaccination to generate causal estimates. He and his co-authors used the fact that flu vaccinations are typically given at well-child visits, which often happen around birthdays. This means that if your child has a birthday around the time the flu vaccine is available, they are more likely to get it. But since birthday month is otherwise unrelated to illness, the authors can use that fact to figure out how much the vaccine matters.

The upshot of this work is that flu vaccines do protect kids from getting the flu, as well as protecting elderly people who live with them from getting the flu and possibly getting very ill. This work has also revealed the best time to get the flu vaccine: October. August seems to be too early (the antibodies wear off before the meat of the flu season), and December is too late (there are already a lot of exposures).

Of course, vaccination at any time is better than never! Just, if you get to pick: October.

A note on pregnancy: This October timing recommendation goes for kids and adults (including older adults). If you are pregnant, there may be value to earlier vaccination if you are due in the fall. Ideally, you’d have at least four weeks between vaccination and birth, to give antibodies time to pass to the baby. That could mean vaccination in September if you’re due in October.

COVID-19

COVID vaccines, at this point, mirror the flu vaccine. The vaccine is reformulated each year to match the best guess of the dominant strain. Although it may not be an exact match, the booster should be close enough to provide good protection against serious illness.

COVID vaccines have been reliably shown to lower risk of hospitalization, serious illness, and death. They have a minimal impact on the risk of getting sick at all, and the impacts on transmitting to others are estimated to be limited. As a result, these vaccines are most valuable for individuals who are at serious risk from COVID. This means older people and those with a compromised immune system. 

In 2025, the FDA has approved COVID vaccination only for those over 65, for individuals who are higher-risk due to at least one underlying medical condition, and for children under 18 after consultation with a doctor. This is a more restrictive approach than in the past, but perhaps not as restrictive as some people fear. The list of conditions for which someone can be eligible includes pregnancy, but also obesity, mental health issues, and physical inactivity. The changes will make it more difficult to get the COVID booster, but it will likely be possible for most people if they want it. 

For older individuals or those with immune compromise, it is a very good idea to get the COVID booster every year (immunity wears off over time). Given the value of passing immunity onto infants, pregnant people are also a good candidate for the booster. For healthy younger adults and children, it is less urgent, and I think reasonable people will make different choices.

P.S.

Many kids are afraid of shots, and this can be a barrier to vaccines, like the flu vaccine, that may feel more “optional.” I love this book for working with younger kids through what to expect and dialing down the fear.

The bottom line

• There is a big spike in the late fall and winter in illness, particularly RSV and the flu. COVID is somewhat less predictable. These illnesses tend to impact older people (65+) most, with RSV also having a high illness rate among the youngest age group (0-4).
• RSV is a common virus that usually causes mild illness but can be dangerous for infants and older adults, making prevention especially important in a baby’s first year of life. 
• There are now two effective options for protection against RSV: Beyfortus, a monoclonal antibody shot given directly to infants, and Abrysvo, a vaccine given during pregnancy to pass protection to newborns. Parents can choose the option that best matches their baby’s birth timing and RSV season.
• Annual vaccination against the flu (starting at 6 months of age) significantly reduces the risk of serious illness in both children and older adults. October is the best time for vaccination (early enough to build protection but not so early that it wears off), though getting the shot at any time is better than not at all. 
• COVID vaccines, at this point, mirror the flu vaccine. The vaccine is reformulated each year to match the best guess of the dominant strain. Although it may not be an exact match, the booster should be close enough to provide good protection against serious illness, which is important, especially for pregnant people, older individuals, or those with immune compromise.

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