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The Booster Dose for COVID-19 Has the Potential to Prevent a Fifth Wave Against the Delta Variant

Updated: Jan 24, 2022

In the USA, according to the World Health Organization (WHO), there have reportedly been 46 million confirmed cases of COVID-19 with 752 thousand deaths, and as of the fifth of November 2021, a total of 450 thousand vaccine doses have been administered [1]. To combat the emerging Delta variant, booster vaccines are currently being administered for a subset of the population, but Pfizer and BioNTech, on November 9th, asked the Food and Drug Administration (FDA) to authorize a booster dose for people 18 and older.

Vaccination against the viral SARS-CoV-2 has been proven to be highly effective against SARS-CoV-2 and especially effective in preventing hospitalisation. However, in a recent July 2021 study involving patients admitted to hospital with a positive SARS-CoV-2 PCR test, researchers found that “nearly a fifth of patients had received at least one dose of the vaccine” and that “more than a quarter of fully vaccinated patients admitted to hospital with SARS-CoV-2 were severely or critically ill with COVID-19” [2]. While some of these patients might have a weaker immune response because of comorbidities such as older age, overweight, and immunosuppressive medications, the breakthrough infections are mostly attributed to new SARS-CoV-2 variants surfacing that have indicated decreased vaccine effectiveness [2]. Certainly, the severity of disease among people who have a breakthrough infection is less severe for people who are vaccinated, but there is a growing concern over the breakthrough infections caused by SARS-CoV-2 variants [3]. The Delta variant specifically is more virulent and extremely transmissible [2]. This has resulted in the USA and Israel already offering booster third vaccine doses.

There has been rising concerns about waning immunity, where a recent October 2021 study from Israel showed a strong relationship between when people became vaccinated and the incidence rate of breakthrough infections, with people vaccinated in January having two times the risk of suffering a breakthrough infection, compared to people who were vaccinated in March [3]. However, there assuredly continues to be minimal risks of contracting severe disease and death by COVID-19 after being vaccinated, no matter when the vaccination was received [2]. Although this waning immunity seems to have a relatively small effect on hospital burden and mortality rates, there is a fear of long-term COVID symptoms from these breakthrough infections, and an overwhelming desire by healthcare personnel and officials to minimize infection rates [4].

Studies in the U.S. and Canada looked at Pfizer’s and Moderna’s vaccines’ effectiveness at preventing infection from Delta. Even though there were different levels of decline, both studies found that both vaccines’ protection dropped over time [4]. But both these studies have found that even after several months, the Pfizer-BioNTech and Moderna vaccines continue to be highly effective at preventing hospitalization [4]. The effectiveness ratings against severe disease and hospitalization have been consistently high, even throughout the recent months against the Delta variant. However, their protection against infection has fallen. Though the vaccine remains more than 50 percent effective at preventing infection, the declines in effectiveness are significantly concerning, sparking the question of whether all adults should get a booster shot [4].

On November 19th, the FDA authorized Pfizer/BioNTech and Moderna booster shots for all adults ages 18 and older [5]. The Centers for Disease Control and Prevention (CDC) has stated that every adult who had their second shot from the Pfizer or Modern vaccine at least six months prior can get a third shot [5]. Additionally, the CDC recommends that people older than 50 or in long-term care settings get the booster shot [5]. The FDA has stated that it is permissible to “mix and match” different vaccines, so someone who received a Moderna vaccine can get a Pfizer booster [5].

Most experts agree that adults over 65 would need the booster because the consequences for waning immunity are higher for these vulnerable populations [4]. Considering that high-risk individuals received their initial vaccines earlier than most, their vaccine effectiveness against infections has decreased. The Israel study examined the effect of the Pfizer booster shot after having the initial two dose five months before, and found that “adding a third dose was estimated to be 93% effective in preventing COVID-19-related admission to hospital, 92% in preventing severe disease, and 81% in preventing COVID-19-related death” [3].

More recently, the World Health Organization (WHO) has identified a new “variant of concern” known as Omicron, which has more than 30 mutations in the spike protein alone, according to Tulio de Oliveira, director of the KwaZulu-Natal Research and Innovation Sequencing Platform [6]. In the fight against SARS-CoV-2, the immune system has been producing antibodies to recognize the virus’s spike protein, so the new mutations have created speculation that Omicron “might be able to evade antibodies produced by either a previous infection or a vaccine” [6]. According to Richard Lessells, an infectious diseases specialist at the KwaZulu-Natal Research and Innovation Sequencing Platform, the Omicron variant has the potential to spread more dangerously with its enhanced transmissibility, and may not be as easily eliminated by our immune system defenses [6].

According to Theodora Hatziioannou, a virologist at Rockefeller University in New York, vaccines can still provide protection against Omicron due to the human body’s innate immunity against infection [7]. The value of new booster shots is to broaden the range of antibodies to target new variants [7]. Moderna has announced that they will address the new SARS-CoV-2 variants of concern, with the emergence of the Omicron variant, and “rapidly advance an Omicron-specific booster candidate” [8].

Looking forward to the winter months, as of November 26, about 59.5% of the US population is fully vaccinated [8]. With the development of boosters as more variants emerge, we can still have hope that this winter and holiday season will be better than last winter when no one was vaccinated. We will all still have to be vigilant and precautious, but the vaccines and booster shots give a fighting chance against the coronavirus.


  1. World Health Organization. (n.d.). United States of America: Who coronavirus disease (covid-19) dashboard with vaccination data. World Health Organization. Retrieved November 15, 2021, from

  2. Juthani, P. V., Gupta, A., Borges, K. A., Price, C. C., Lee, A. I., Won, C. H., & Chun, H. J. (2021). Hospitalisation among vaccine breakthrough COVID-19 infections. The Lancet. Infectious diseases, 21(11), 1485–1486.

  3. Barda, N., Dagan, N., Cohen, C., Hernán, M. A., Lipsitch, M., Kohane, I. S., Reis, B. Y., & Balicer, R. D. (2021). Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study. Lancet (London, England), S0140-6736(21)02249-2. Advance online publication.

  4. Walker, A. S., & Holder, J. (2021, November 11). What we know so far about waning vaccine effectiveness. The New York Times. Retrieved November 15, 2021, from

  5. Piper, K. (2021, November 19). Two confusing questions about covid-19 boosters, answered. Vox. Retrieved November 21, 2021, from

  6. Chutel, L. (2021, November 26). Here's what we know about the Omicron variant. The New York Times. Retrieved November 26, 2021, from

  7. Zimmer, C. (2021, November 26). New virus variant stokes concern but vaccines still likely to work. The New York Times. Retrieved November 26, 2021, from®i_id=88650726&segment_id=75510&user_id=3eb9607ad2e8267c364d870767164e78.

  8. Moderna announces strategy to address omicron (b.1.1.529) SARS-COV-2 variant. Moderna, Inc. (2021, November 26). Retrieved November 26, 2021, from

  9. Mayo Foundation for Medical Education and Research. (n.d.). U.S. COVID-19 vaccine tracker: See your state's progress. Mayo Clinic. Retrieved November 26, 2021, from

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