Third COVID Vaccine Dose: Safety and Recommendations for Mixed Vaccination

Third dose of the COVID-19 vaccine?

Hello: My mother is 73 years old.
She received the first dose of the AZ vaccine and the second dose of the BNT vaccine.
She is now looking to get the third dose, but the hospitals and clinics no longer have BNT available.
Some doctors and researchers from the National Health Research Institutes believe that it is not advisable to receive a third dose from a different manufacturer.
For those who received AZ and BNT for the first two doses, the third dose should be AZ + BNT + BNT.
I would like to ask: 1.
Is it safe for my mother to receive the Moderna vaccine as the third dose? Will the protection be strong enough? 2.
Are there any studies or recommendations, either domestically or internationally, regarding the third dose for those who have mixed vaccine regimens for the first two doses? I appreciate your clarification, thank you~~

A-Du, 40~49 year old female. Ask Date: 2022/03/31

Dr. Hong Yuanbin reply Internal Medicine

Hello, based on some domestic and international studies, the third dose of Moderna is safe and provides strong protection.
For individuals who received mixed vaccines for the first two doses, it is generally recommended to receive an mRNA vaccine for the third dose, either BNT (Pfizer-BioNTech) or Moderna.
Thank you for your inquiry.

Reply Date: 2022/03/31

More Info

When considering the administration of a third COVID-19 vaccine dose, particularly in the context of mixed vaccination regimens, it is essential to evaluate both safety and efficacy. Your mother's vaccination history—receiving the AstraZeneca (AZ) vaccine as the first dose and the Pfizer-BioNTech (BNT) vaccine as the second dose—places her in a category that has been the subject of extensive research regarding mixed vaccine schedules.

1. Safety and Efficacy of Moderna as the Third Dose:
Current evidence suggests that administering the Moderna vaccine as a third dose after receiving AZ and BNT is safe. Studies have indicated that mixed vaccination regimens can elicit robust immune responses. For instance, a study published in the journal *Nature* found that individuals who received different vaccines showed higher levels of neutralizing antibodies compared to those who received the same vaccine for all doses. This implies that using Moderna as a third dose could potentially enhance the immune response, providing strong protection against COVID-19.

Moreover, the safety profile of the Moderna vaccine is well-documented. Common side effects include pain at the injection site, fatigue, headache, and mild fever, which are generally short-lived. Serious adverse events are rare, and the benefits of vaccination in preventing severe illness, hospitalization, and death from COVID-19 outweigh the risks associated with vaccination.

2. Recommendations for Mixed Vaccination:
Both domestic and international health authorities have recognized the potential benefits of mixed vaccination schedules. The Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) have provided guidance that supports the use of different vaccines for initial and booster doses. For individuals who have received a combination of vaccines, such as AZ followed by BNT, it is generally recommended to receive an mRNA vaccine (like BNT or Moderna) for the third dose.

Research has shown that mixed vaccination can lead to a more robust immune response. For example, a study conducted in Spain demonstrated that individuals who received a combination of AZ and BNT had higher antibody levels after their second dose compared to those who received two doses of the same vaccine. This trend is encouraging and supports the idea that using different vaccine platforms can be beneficial.

In conclusion, your mother's plan to receive the Moderna vaccine as her third dose appears to be a safe and effective choice, especially given her previous vaccinations. It is important to consult with her healthcare provider to ensure that her specific health conditions and any potential contraindications are taken into account. The evolving landscape of COVID-19 vaccination continues to be informed by ongoing research, and mixed vaccination strategies are increasingly being recognized as a viable approach to enhancing immunity against the virus.

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