When to Get the 2024-2025 Updated COVID-19 Vaccine

The FDA has authorized two new COVID-19 vaccines (Pfizer and Moderna) and is expected to authorize a third (Novavax) in the coming weeks. It is anticipated that the Pfizer and Moderna vaccines may start showing up in some pharmacies as soon as this weekend, with much more availability during the course of next week.

What is different about these vaccines?

All three vaccines are monovalent vaccines, which means that they are based on the spike protein of just one variant. All three vaccines are based on different and more recently occurring variants than the variant that served as the basis for the 2023-2024 updated vaccines that were made available last September (XBB.1.5). The Novavax vaccine that is awaiting authorization is based upon JN.1 and the Pfizer and Moderna vaccines are both based on the KP.2 variant.

Are these new vaccines booster shots?

Technically, no. A booster is another dose of the same vaccine previously administered in order to boost the specific immune response generated by that prior dose of vaccine. In this case, because all three vaccines are new formulations based on more recent variants, they are technically priming doses and will result in new immune cells developing in response to the new variant’s spike protein. For those (see below) who are eligible for a second dose of this vaccine due to age or underlying medical conditions, that second dose next year will be a booster.

Having provided the technically correct answer, there are ways that this priming dose does act in some respects as a boosting dose. For example, let’s assume that you were infected early this year. That infection was very likely due to JN.1 as it was so fit that it basically outcompeted all the other circulating variants and became dominant. If you survived the infection and have a healthy immune system, then you developed an immune response to the JN.1 spike protein. If you were to get the Novavax updated vaccine next month when we expect it to be authorized, then this priming dose will significantly boost the immune response you generated from that prior infection.

The other way in which these priming vaccines will still act in a conceptual way as a “booster” is that there are many parts of the spike protein that serve as antigens (meaning that our immune systems recognize them as not us and something to form antibodies against), and some of those antigens will still be in the new spike protein formulation, and there are other parts of the spike protein that stimulate another part of our immune system that is particularly important in protecting us from severe disease and in clearing the virus from our system that gets boosted with each dose of vaccine we get.

Who can get the new COVID-19 vaccines?

The FDA has authorized the new 2024-2025 Pfizer and Moderna COVID-19 vaccines for those 6 months old and older. The CDC has recommended that everyone 6 months of age and older receive an updated COVID-19 vaccine.

When should you get the new vaccine?

The answer to this question depends in large part on your specific risks, so check with your doctor, but here are some considerations:

1. If you received a second dose of the 2023-2024 updated COVID-19 vaccine (likely due to your age or underlying medical conditions) within the last two months, the CDC’s guidance is to wait until a full two months after that shot to get the new updated vaccine.
2. If you have had COVID-19 within the past three months, the CDC guidance is to wait for a full three months after infection to get the new vaccine.
3. If you are over age 65 or have underlying medical conditions, and especially if you fit into both categories and/or are immunocompromised, and you have not had COVID or a COVID vaccine in the past year, your immune protection has likely significantly waned, and therefore, you should seriously consider getting the new vaccine ASAP, especially since we are experiencing high levels of community transmission.
4. If you have had or have Long COVID, your risks for returning symptoms or worsening of symptoms appears to be increased with another infection, and therefore, you should discuss with your doctor whether you should get the new vaccine now and a second dose in 4-6 months.
5. If you are pregnant, you are at risk for more severe disease than a woman your age who is not pregnant, and there are risks to your unborn child, so discuss the timing for getting the new vaccine with your obstetrician or whichever health care professional is managing your pregnancy care.
6. If you have upcoming travel plans, especially to a foreign country, and want to minimize the chances of illness and hospitalization away from home, consider timing your new vaccine dose at 10 – 14 days prior to your departure. The same advice would be relevant if you have an upcoming event, e.g., a wedding, where there will be a lot of guests, especially many travelling to the event, due to the increased risk of exposures.
7. If you have had significant reactions to the mRNA vaccines (Pfizer or Moderna) or your doctor has advised you not to take them due to a reaction, or if you merely are concerned about mRNA vaccines, you may wish to wait for the Novavax vaccine to become available, which as stated above, is expected in the upcoming weeks. Novavax is a protein subunit vaccine that has a long history of use in making various vaccines and contains no mRNA. It also is much less likely to cause the same degree of side effects (sore arm, swelling, fever, muscle aches) than the mRNA vaccines.
8. For everyone else, this is a tougher question to answer. Right now, levels of transmission are high throughout most of the U.S., however, it appears that we may have just reached the peak and may be headed down. If you are not at high-risk, have kept up with the recommended vaccines, and are able to employ non-pharmaceutical measures to minimize your exposures (for example, working from home, masking when out in public crowds, avoiding large indoor gatherings, etc.) until the levels of community spread decrease significantly, then you may very well want to wait until the next new variant begins to make a surge here in the U.S. (there is already a new variant that is circulating in Europe, but it doesn’t appear to be spreading significantly here in the U.S. yet) in order to try to line-up your highest immune response to the time of greatest risk of infection, especially because if you are in this group, you are unlikely to qualify for a booster dose in the first half of next year, then waiting for the next surge to begin could be a reasonable option.

Which vaccine should you get?

Unless you fall into category 3, 4, 5, 6, or 7, in which case you should not wait for Novavax and get either one of the mRNA vaccines depending upon the advice of your physician, this is a really difficult question to answer, and in fact, there is no correct answer. We do not have recent studies that test these vaccines in head-to-head comparisons.

There is suggestive, but not conclusive, data to support that mixing up the vaccines (such that if you have always received the Pfizer vaccine, to now get a Moderna vaccine, and vice versa) might result is a somewhat broadened antibody response, though the data is not so clear-cut as to make this a formal recommendation. Frankly, if you have tolerated one vaccine in the past, just go ahead and get that one again. On the other hand, if one of the mRNA vaccines caused significant side effects, try the other, or if you are not at high-risk as I described above, consider waiting for the new Novavax vaccine to come out.

The tricky part of the question is whether the mRNA vaccines (based on KP.2) or the Novavax vaccine (based on JN.1) will be most protective against the variants that will emerge over the course of the next year. That is because we don’t know how this virus will mutate and/or recombine in the near future. There is a case to be made for advocating for either option, and in fact, members of the vaccine committee that made its recommendations to the FDA and vaccine manufactures were not all in agreement on this. The arguments for the mRNA vaccines (KP.2) include the fact that KP.2 is more recent than JN.1 and the fact that this variant developed some new, more immune evasive mutations, and since that contributed to increased fitness, those mutations may be more likely to be reappearing in new future variants. However, the exception to that rule already happened in the subsequent variant that followed KP.2 – KP.3.

The other school of thought relates to the evolutionary biology of viruses, and particularly the SARS-CoV-2). If you think of the evolutionary tree much the way you might think of a family tree with which readers are likely more familiar, that tree has a trunk that begins with the oldest ancestor(s), and then has branches that grow off of it depending on the degree of relatedness. Unlike family trees, the evolutionary tree for viruses is not always linear, and this is especially true of SARS-CoV-2. Thus, while one branch seems to be progressing and growing with serial minor genetic mutations, all of a sudden, we see a new variant that is different enough that it is starting a new branch. Thus, this school of thought argues that using the trunk of the tree (in this case JN.1 from which all of the variants we have experienced since the beginning of this year are descendants) would likely result in a closer match to future variants than basing the vaccine on a variant that is from a branch (e.g., KP.2).

You’ll find vaccine experts that are proponents on both sides of the argument, and the fact is that we just don’t know. Time will tell, but two things do appear clear to us. One is that now into our fifth year of the pandemic, every dose of past vaccines has added protection against severe disease – hospitalization and death – no matter how well or poorly matched to the circulating variant at the time of infection. The other is that getting the vaccine reduces your risk of Long COVID by as much as 50 percent. Recall that every infection you get, increases your risk for Long COVID. So, don’t agonize over this decision. Any vaccine is better than no vaccine, and we have every reason to believe that any of these vaccines will reduce your risks for severe disease and Long COVID.