COVID-19 Bivalent Booster

In keeping up with the most recent Omicron subvariants of COVID-19 surging in the U.S., the CDC is recommending new vaccine boosters that became available in early September. Here are answers to the most common questions my patients are asking about these new vaccines.

1. How are the new COVID-19 booster vaccines different from the original vaccines?

Moderna and Pfizer-BioNTech have produced “updated” mRNA booster vaccines for COVID-19. These vaccines have recently been authorized by the FDA and are now recommended by the CDC as booster vaccines for previously vaccinated individuals to provide better protection against COVID-19.

Both boosters are called bivalent vaccines, which means that they contain two messenger RNA (mRNA) components of the SARS-CoV-2 virus that causes COVID-19. The mRNA in these bivalent vaccines gives instructions to cells in the body to make two versions of the viral spike protein: the spike protein from the original virus strain and the spike protein that is shared by the most recent omicron subvariants BA.4 and BA.5.

As I discussed in a previous blog, the immune response to the initial vaccines slowly fades over time and this waning immunity can be restored with additional booster vaccination doses. In addition to waning immunity, variants of the SARS-CoV-2 virus have emerged, and these variants have undermined the protection conferred by the original COVID-19 vaccines. Omicron subvariants, specifically BA.4 and BA.5, are the most common viruses causing COVID-19 in the United States and are likely to be the dominant viruses if we have an expected surge of COVID-19 infections this fall and winter when people spend more time indoors and in close contact with each other.

The new boosters are designed to retain protection against the original SARS-CoV-2 virus while creating stronger immune responses to the current Omicron subvariants. Hopefully, the new booster vaccines will also provide immunity that lasts for a longer period of time, and they might prepare the immune system to respond to variants more effectively.

2. Why didn’t the new booster go through the same clinical trials as the original COVID-19 vaccines?

The FDA did not require the same detailed clinical trial data before it granted authorization to the new bivalent booster vaccines. This is because the original mRNA COVID-19 vaccines have already been studied extensively and safely administered to millions of people around the world. Since Moderna and Pfizer-BioNTech are using the same mRNA vaccine technology to make their vaccines and are making only small adjustments in the mRNA information to accommodate changes in the spike proteins shared by the BA.4 and BA.5 subvariants, they do not need to undergo the same large clinical trials to demonstrate safety and efficacy. This is the same approach that is taken for the approval of influenza vaccines every year. Influenza vaccines are adjusted on an annual basis to accommodate changes in the flu virus, and these reformulated vaccines do not need to be fully tested in a clinical trial before they are approved by the FDA and administered to millions of people.

Clinical trials would take too long to complete and unnecessarily delay the availability of new vaccines that target the most common circulating coronavirus variants. We need to stay a step ahead and move quickly to offer new vaccines that are both timely and effective against variants, while not compromising safety or public confidence. These are huge challenges for both vaccine manufacturers and public health officials.

Safety of mRNA vaccines has been clearly established, with extremely rare reports of serious adverse events. Remember that common side effects, like a sore arm, muscle aches, and fever, are normal symptoms when your immune system is activated and are not considered a serious adverse reaction. All of the available data, including human bivalent vaccine studies with the original Omicron variant (BA.1), were carefully reviewed by the FDA and used as the basis for approval of the new mRNA vaccine boosters.

Efficacy of the vaccine, however, will be more difficult to determine since much of the data about the vaccine’s ability to prevent COVID-19 illness will not be available for a while. This is similar to our experience with influenza vaccines. Some years, the influenza vaccine provides excellent protection (matching the circulating strains of influenza virus that year and producing a strong immune response), while other years, it demonstrates much less efficacy in preventing influenza illness. However, even in a year of poor influenza vaccine efficacy, the efficacy is never zero, and vaccinated individuals still have some protection, especially for serious illness. Similarly, the COVID-19 bivalent boosters will almost certainly offer additional protection, especially toward serious illness and hospitalizations related to COVID-19, but there is no way to know today how effective it will be by the end of the winter or into the springtime. We also do not know if additional variants will emerge that again undermine vaccine efficacy.

3. Who should get the new booster?

The CDC is strongly recommending that all previously vaccinated adults and adolescents receive the new bivalent booster at least 2 months after their last COVID-19 vaccine (either the primary vaccination series or a recent booster dose with the original vaccine). The Pfizer-BioNTech booster is authorized by FDA for ages 12 and older. The Moderna booster is authorized only for ages 18 and older.

Some vaccine experts have raised questions about recommending the new boosters to all adults and adolescents, based on the lack of efficacy data and questions about optimal timing to account for waning immunity and possible surges in COVID-19 infections. However, the counter argument is that certain populations, like older adults, are at particularly high risk for complications related to COVID-19, including hospitalizations and death. Since the vaccine protection wanes more rapidly in older adults, boosters are even more important for older individuals. A booster that targets the most common variants is a rational approach to offer the most protection. Considering the excellent safety profile of the mRNA vaccines, I have no hesitation in recommending the new bivalent COVID-19 booster vaccine to my older adult patients and for others at high risk of COVID-19 complications. For younger adults and those in good health, the decision to get a booster (and the timing of that booster) may be motivated either by a desire to protect vulnerable individuals with whom they have regular contact or simply by a desire to protect themselves from COVID-19 infections. Like the original vaccine, it takes about 2 weeks after the booster vaccine to see antibody levels rise to the highest levels and confer the most protection.

4. Do I need the booster if I already had two boosters? What if I had only one previous booster?

Yes, the CDC recommends that you receive the new updated bivalent COVID-19 booster vaccine if it has been at least 2 months since your last booster dose. In fact, the CDC has revised their definition of “up to date” COVID-19 vaccination to include the new booster. If you have never received a booster or have received only one booster, you should still get the updated bivalent booster to protect yourself from the most common variants that will likely cause infections this fall and winter. The original mRNA vaccines are no longer approved for booster doses. Only the new bivalent mRNA vaccines should be used for booster doses.

5. What if I recently had COVID-19, do I still need to get the updated booster?

Yes! The immune response from COVID-19 can vary greatly and does not necessarily result in long-term protection. It is likely that your recent COVID-19 infection was due to either the BA.4 or BA.5 subvariants, so it is reasonable to believe that you have at least short-term protection against reinfection. However, since that immunity will wane over time, getting a booster is still important. At a minimum, the CDC recommends that you wait to get a COVID-19 vaccine, including the bivalent booster vaccine, until you have recovered from your acute COVID-19 illness, and you have met criteria to discontinue isolation. However, it may be reasonable to wait 3 months from symptom onset (or positive test if you were asymptomatic) before getting one of the bivalent booster vaccines. Do not wait too long, however, since the protection you may have gained from prior infection could be too low to protect you during a surge this coming winter. For individuals at higher risk of severe COVID-19 disease and for those with compromised immune systems, I would encourage a discussion with their physicians about earlier booster vaccination and other COVID-19 prevention strategies.

6. What are the side effects of the new booster?

Side effects for an earlier version of the bivalent mRNA vaccine were very similar to the original vaccine and boosters. No new concerns were raised regarding vaccine safety. Pain, redness, and swelling at the injection site are common local reactions. Adults also can develop low-grade fever, chills, muscle aches, and fatigue. Fortunately, these side effects are generally mild and typically go away in about a day or two. Serious reactions to the COVID-19 vaccines, even after booster doses, remain extremely rare. If you had mild to moderate side effects from your previous COVID-19 vaccine, you will likely have a similar experience with a booster dose. Remember that many of these local reactions and systemic side effects are signals that your body is responding to the vaccine and developing a stronger immune response.

7. Can I mix and match vaccines?

The FDA has previously authorized the use of “mix-and-match” booster doses. As with the use of the original COVID-19 vaccines for booster doses, either of the new bivalent mRNA COVID-19 vaccines from Moderna and Pfizer-BioNTech can be administered regardless of which mRNA you originally received or were most recently boosted with. The decision of which of the new vaccine boosters you receive may be determined either by availability of vaccine or personal preference. Some people may decide to stay with the same vaccine manufacturer for all of their vaccine doses, including booster doses, but this is merely personal preference. Mix and match might be a more practical approach if you have easier access to a vaccine that is from a manufacturer that is different from your previous doses. Much like my recommendations for influenza vaccine, I recommend getting COVID-19 vaccination whenever you can access an approved vaccine. Otherwise, you run the risk of missing the opportunity to get vaccinated, and you also do not know if there could be problems later on with either vaccine supply or access.

The CDC still does not recommend mixing products for your primary (initial) vaccine series. After you completed your 2-dose vaccine, you may mix and match for your booster dose as long as at least 2 months have passed since you completed the primary vaccine series. If you received Novavax, the Johnson & Johnson (Janssen) vaccine, or another vaccine outside of the U.S. that has not approved by the FDA, you should talk to your doctor about recommended booster doses.

8. Should I still get the influenza vaccine this year?

Yes! Influenza continues to cause serious illness, especially for older adults. Annual vaccination for influenza is very important to protect yourself. It is safe to get both the COVID-19 booster and your annual influenza vaccine at the same time but in different arms. Since you can develop local and systemic reactions to either vaccine, it may be desirable to get the vaccines on different days. In the rare event that you had a more serious adverse event related to one of the vaccines, it can also be more difficult to sort out which vaccine caused the problem, although this is a highly unlikely scenario. However, if you think you might have difficulty with accessing vaccines (for example, transportation challenges), then getting both vaccines at the same time might be a wise strategy, so that you do not delay or miss a vaccine. Ideally, influenza vaccination should occur by the end of October, but you can receive the vaccine at any time when the influenza vaccine is available.

9. Do I need to wear a mask after I receive the updated bivalent booster?

Mask mandates have been removed for most settings, except for hospitals, nursing homes, and other healthcare facilities. However, you may still decide to wear a mask to protect yourself in public settings, especially when the risk of infection is high or if you have medical conditions that put you at increased risk of COVID-19 complications. The CDC’s community level for COVID-19 is one measure that can help guide your decision to wear a mask. You can review information for any county in the U.S. and review advice about personal precautions.

Remember that vaccines for COVID-19 are only one tool to help protect yourself and other people from infection. Although previous COVID-19 vaccines have shown to be highly efficacious, no vaccine provides 100% protection. Even if you do not develop symptoms of COVID-19 or have only mild symptoms, you can still infect other people. Wearing a mask when you are in close contact with unvaccinated persons, immunocompromised persons, or those at high risk of COVID-19 complications can be a good way to protect them. It is particularly important to wear a mask if you have symptoms that could be related to COVID-19, had a recent exposure to someone with COVID-19, are awaiting COVID-19 test results, or have recently recovered from COVID-19 illness.

10. How many more boosters will I need? Can we keep up with this virus by making new boosters?

The virus that causes COVID-19 continues to cause infections and change over time. At a minimum, I suspect that we will need annual COVID-19 vaccination to stay ahead of changes in the viruses from year to year and to address the decreasing (waning) immunity that is observed with many vaccines. If you want to protect yourself and those close to you, it looks like influenza and COVID-19 vaccination will both be part of your annual health rituals for the foreseeable future.

Anthony J. Caprio, MD, is medical director at Sharon Towers and geriatrician at Atrium Health. The opinions expressed by Dr. Caprio in this article are his own and not necessarily those of Atrium Health.

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