This evidence synthesis has been compiled by members of the CITF Secretariat and does not necessarily represent the views of all CITF members.

By Mariana Bego 

The clinical efficacy of several vaccines in protecting against symptomatic COVID-19, especially in light of the circulating variants, has been an emerging research topic. Several articles referring to this ongoing subject of interest were recently published in Nature with promising results. More specifically, these studies reported the neutralization of several variants, including Delta, by the Pfizer-BioNTech vaccine, as well as an observation of antibody and cellular immune protection against several variants elicited by the Johnson & Johnson vaccine.


Key points:

– The Pfizer-BioNTech COVID-19 vaccine is capable of neutralizing several variants including Delta (B.1.617.2) and Eta (B.1.525).

– The Johnson & Johnson COVID-19 vaccine elicited neutralizing antibody titers against variants Beta (B.1.351) and Gamma (P.1). While this neutralization was observed to be lower for these variants as compared to the original SARS-CoV-2 virus, the functional non-neutralizing antibody responses and T cell responses were comparable across the original virus, Alpha (B.1.1.7), Beta, Gamma, and Iota (B.1.526) variants.


In a recent Nature article, Liu and colleagues reported that blood samples from 20 individuals, collected after two doses of the Pfizer vaccine, contained antibodies capable of neutralizing the original SARS-CoV-2 virus, as well as several variants including Delta, Kappa (B.1.617.1), B.1.618, and Eta (B.1.525). The authors conclude because vaccines are proving to effectively neutralize SARS-CoV-2 and many, if not most, variants to date, global vaccination is a central strategy to end the COVID-19 pandemic.1

The Johnson & Johnson COVID-19 vaccine has demonstrated clinical efficacy against symptomatic COVID-19, including against Beta, a variant that is partially resistant to neutralizing antibodies.2 Alter and colleagues recently reported in Nature about humoral and cellular immune responses from 20 Johnson & Johnson COVID-19 vaccine recipients against the original SARS-CoV-2 virus as well as against several variants: Alpha, Beta, Gamma, and Iota. The neutralizing antibody titers against variants Beta and Gamma were lower than against the original SARS-CoV-2 virus on day 71 following vaccination. While neutralizing antibody responses induced by this vaccine were reduced against these variants, functional non-neutralizing antibody responses and T cell responses were comparable for all the SARS-CoV-2 variants tested, i.e., Alpha, Beta, Gamma, and Iota.3

Although the relevance of these immune parameters as correlates of protection remains to be determined, the authors of these studies remain optimistic about the potential effectiveness of this vaccine against variants of concern. Nevertheless, physical barriers like masks and social distancing remain necessary and must be part of the risk-mitigation COVID strategy, particularly until two weeks after the second dose of the COVID-19 vaccine has been administered.

Scientists from Israel’s Clalit Health Services and collaborators tested whether variants of concern currently circulating in Israel were able to evade the protection provided by the Pfizer-BioNTech COVID-19 vaccine. Many of the infections observed within the time window between the first and second vaccine doses were attributed to variants Alpha and Beta.4 The authors emphasize the importance of rigorously tracking variants and of completing the two-dose regime to prevent infection and wider spread.



  1. Liu J, Liu Y, Xia H, Zou J, Weaver SC, Swanson KA, Cai H, Cutler M, Miuk A, Jansen KU, Sahin U, Xie X, Dormitzer PR, Shi PY. BNT162b2-elicited neutralization of B.1.617 and other SARS-CoV-2 variants. Nature. 2021 Jun 10. doi: 10.1038/s41586-021-03693-y.
  2. Sadoff J, Gray G, Vandebosch A, Cardenas V, Shunkarev G, Grinsreijn B, Goepfert PA, Truyers C,  Fennema H,  Spiessens B, Offergeld K, Scheper G, Taylor KL, Robb ML, Treanor J, Barouch DH, Stoddard J, Ryser MF, Marovich MA, Neuzil KM, Corey L, Cauwenberghs N, Tanner T, Hardt K, Ruiz-Guiñazú J, Le Gars M, Schuitemaker H, Van Hoof J, Struyf F, Douoguih M,  for the ENSEMBLE Study Group. Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19. N Engl J Med. 2021 Jun 10. doi: 10.1056/NEJMoa2101544.
  3. Alter G, Yu J, Liu J, Chandrashekar A, Borducchi EN, Tostanoski LH, McMahan K, Jacob-Dolan C, Martinez DR, Chang A, Anioke T, Lifton M, Nkolola J, Stephenson KE, Atyeo C, Shin S, Fields P, Kaplan I, Robins H, Amanat F, Krammer F, Baric RS, Le Gars M, Sadoff J, Marit de Groot A, Heerwegh D, Struyf F, Douoguih M, van Hoof J, Schuitemaker H, Barouch DH. Immunogenicity of Ad26.COV2.S vaccine against SARS-CoV-2 variants in humans. Nature. 2021 Jun 9. doi: 10.1038/s41586-021-03681-2.
  4. Kustin T, Harel N, Finkel U, Perchik S, Harari S, Tahor M, Caspi I, Levy R, Leshchinsky M, Ken Dror S, Bergerzon G, Gadban F, Gadban F, Eliassian E, Shimron O, Saleh L, Ben-Zvi H, Keren Taraday E, Amichay D, Ben-Dor A, Sagas D, Strauss M, Shemer Avni Y, Huppert A, Kepten E, Balicer RD, Netzer D, Ben-Shachar S, Stern A. Evidence for increased breakthrough rates of SARS-CoV-2 variants of concern in BNT162b2-mRNA-vaccinated individuals. Nat Med. 2021 Jun 14. doi: 10.1038/s41591-021-01413-7.