Rollout of Bivalent COVID Booster

November 2, 2022

To combat the COVID-19 pandemic, scientists developed more than 150 vaccine candidates at unprecedented speeds in 2020 (1). In the United States, the first vaccine regimens approved by the Food and Drug Administration (FDA) included the Moderna and Pfizer vaccines which both administered messenger RNA (mRNA) derived from SARS-CoV-2, the strain first identified at the beginning of the outbreak (2). While these vaccines showed strong efficacy of approximately 95% against the original COVID-19 strain (3), novel variants of the virus began to circulate around the world by the end of 2020. Recently, a bivalent COVID booster was approved, with rollout now occurring throughout the US. 

Containing mutations in the spike protein that helped circumvent the immunity induced by the vaccines, variants of concern (VOCs) appeared significantly more infectious and were shown to be more capable of escaping neutralizing antibodies induced by vaccination or previous infection (4). Compared to the ancestral strain, a number of critical variants demonstrated significantly higher transmissibility, from an increase of 25% for beta (B.1.351) to a shocking increase of 95% for delta (B.1.617.2) (5). Because the vaccines were formulated to protect against the ancestral variant, they showed significantly lower efficacy against the mutated variants (6). While vaccines continue to prevent severe disease, they have been significantly less effective against infection from these variants, in addition to the omicron variant, even in fully vaccinated individuals (6). Therefore, scientists developed a new vaccine to specifically prevent infection from these variants. 

The new vaccine that is undergoing national rollout, known as the “bivalent vaccine” or the “updated booster,” utilizes two forms of messenger RNA — one part derived from the ancestral strain, and one part derived from the B.4 and B.5 omicron variants (7). Similar to seasonal flu shots, the updated COVID-19 booster was designed to target the strain that is predicted to dominate in coming months (8). The addition of the omicron mRNA allows the new booster to induce immune responses against the most common strain currently circulating in the United States as well as the less transmissible but common variants from the original lineage (7). Offered by Moderna and Pfizer, the booster is expected to confer elevated efficacy against variants compared to the original vaccines (7). Although the efficacy of the boosters remains to be confirmed by large, real-world datasets, studies have shown that the boosters produce more antibodies against the omicron variants than the initial two-dose regimen (7). While the introduction of the updated boosters was met with concern about safety, researchers assert that the boosters do not cause worsened side effects compared to the typical vaccines (9).  

The FDA issued an Emergency Use Authorization for the two versions of the updated booster in August 2022 to prepare for an increase in omicron cases in winter (8). Following this approval, the Centers for Disease Control and Prevention recommended that individuals aged 5 and older should receive the booster at least two months after completing a two-dose regimen, even if they have already received the previous booster (10). 

However, according to recent polls, the public appears unaware of the new boosters, with approximately 51% of respondents indicating that they have heard “a little” or “nothing at all” about the shots (11). Although tens of millions of doses have been delivered to tens of thousands of sites around the country, only 1.5% of Americans have received the updated booster as of September 2022 (12).  

Researchers blame the lack of awareness and low vaccination rates on the increasing sense of normalcy in light of reduced COVID-19 restrictions (13). However, based on statistical modeling, researchers hypothesize that omicron variants will surge in winter 2022 (8). Therefore, the FDA and CDC continue to recommend obtaining an updated booster shot to avoid this predicted increase.  

To increase booster vaccination rates, researchers recommend that health care providers discuss the bivalent COVID booster with their patients, administer vaccine information, and help host vaccination events to facilitate rollout (14). While the updated boosters show promise in protecting against COVID-19 variants, awareness must be increased to prevent the uptick in omicron cases on the horizon. 


1: Kaur, S. and Gupta, V. (2020). COVID-19 vaccination: a comprehensive status report. Virus Research vol. 288. DOI: 10.1016/j.virusres.2020.198114. 

2: Ying, B., Whitener, B., van Blargan, L., Hassan, A., Shrihari, S., Liang, C., Karl, C., Mackin, S., Chen, R., Kafai, N., Wilks, S., Smith, D., Carreno, J., Singh, G., Krammer, F., Carfi, A., Elbashir, S., Edwards, D., Thackray, L., Diamond, M. (2021). Science Translational Medicine, vol. 14. DOI: 10.1126/scitranslmed.abm3302.  

3: Malik, J., Ahmed, S., Mir, A., Shinde, M., Bender, O., Alshammari, F., Ansari, M., Anwar, S. (2022). The SARS-CoV-2 mutations versus effectiveness: new opportunities to new challenges. Journal of Infection and Public Health, vol. 15. DOI: 10.1016/j.jiph.2021.12.014. 

4: Bekliz, M., Adea, K., Vetter, P., Eberhardt, C., Hosszu-Fellous, K., Vu, D., Puhach, O., Essaidi-Laziosi, M., Waldvogel-Abramowski, S., Stephan, C., L’Huillier, A., Siegrist, C., Didierlaurent, A., Kaiser, L., Meyer, B. and Eckerle, I. (2022). Neutralization capacity of antibodies elicited through homologous or heterologous infection or vaccination against SARS-CoV-2 VOCs. Nature Communications, vol. 13. DOI: 10.1038/s41467-022-31556-1.  

5: Campbell, F., Archer, B., Laurenson-Schafer, H., Jinnai, Y., Konings, F., Batra, N., Pavlin, B., Vandemaele, K., van Kerkhove, M., Jombart, T., Morgan, O. and de Waroux, O. (2021). Increased transmissibility and global spread of SARS-CoV-2 variants of concern as at June 2021. Eurosurveillance, vol. 26. DOI: 10.2807/1560-7917.ES.2021.26.24.2100509. 

6: Zeng, B., Gao, L., Zhou, Q., Yu, K. and Sun, F. (2022). Effectiveness of COVID-19 vaccines against SARS-CoV-2 variants of concern: a systematic review and meta-analysis. BMC Medicine, vol. 20. DOI: 10.1186/s12916-022-02397-y.  

7: Chalkias, S., Harper, C., Vrbicky, K., Walsh, S., Essink, B., Brosz, A., McGhee, N., Tomassini, J., Chen, X., Chang, Y., Sutherland, A., Montefiori, D., Girard, B., Edwards, D., Feng, J., Zhou, H., Baden, L., Miller, J. and Das, R. (2022). A bivalent omicron-containing booster against COVID-19. New England Journal of Medicine, vol. 387. DOI: 10.1056/NEJMoa2208343.  

8: Callaway, E. (2022). Will there be a COVID winter wave? What scientists say. Nature News Explainer. URL: 

9: Polack, F., Thomas, S., Kitchin, N., Absalon, J., Gurtman, A., Lockhart, S., Perez, J., Marc, G., Moreira, E., Zerbini, C., Bailey, R., Swanson, K., Roychoudhury, S., Koury, K., Li, P., Kalina, W., Cooper, D., Frenck, R., Hammitt, L., Tureci, O., Nell, H., Schaefer, A., Unal, S., Tresnan, D., Mather, S., Dormitzer, P., Sahin, U., Jansen, K., Gruber, W. (2020). Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine. New England Journal of Medicine, vol. 383. DOI: 10.1056/NEJMoa2034577.  

10: Centers for Disease Control and Prevention. (2022). Stay up to date with vaccines. CDC release. URL:  

11: Sparks, G., Lopes, L., Hamel, L., Montero, A., Presiado, M. and Brodie, M. (2022). KFF COVID-19 vaccine monitor: September 2022. Poll. URL:  

12: Haines, M. (2022). Many Americans in no rush to get bivalent booster. VOA News. News article. URL:  

13: Brenan, M. (2022). Roundup of Gallup COVID-19 coverage. Gallup. News article. URL:  

14: Centers for Disease Control and Prevention. (2022). Ways to help increase COVID-19 vaccinations. CDC release. URL: