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

Authors of a recent modelling-based study in Nature Medicine suggest the levels of neutralizing (infection-blocking) antibodies in blood are highly predictive of the strength of immune protection. The team used a model to compare the efficacy of eight vaccines and to study antibody wane. They predict boosters will be needed about a year after the second dose of a two-dose regime.


Key points:

  • High levels of SARS-CoV-2 neutralizing antibodies (obtained from previous infection or vaccination) are a strong indicator of how protected a person is from COVID-19.
  • mRNA vaccines including the Pfizer-BioNTech and Moderna, as well as the protein subunit vaccine from Novarax, appear to be the most protective of the eight vaccines studied, while CoronaVac appears as the least protective of the eight.
  • Antibodies wane over time and boosters may be needed a year after the second dose of a two-dose regimen.


Models that can predict immune protection from COVID-19 are needed to guide the world’s pandemic response, including vaccine deployment. In a recent study published in Nature Medicine, Khoury and colleagues modeled the relationship between levels of SARS-CoV-2 neutralizing antibodies Antibodies that bind to the surface structures of a pathogen, preventing it from entering and infecting its host cells. and protection towards COVID-19. For their model, the authors gathered data from individuals who recovered from natural SARS-CoV-2 infection as well as participants from eight vaccines trials (Moderna, Pfizer, AstraZeneca, Covaxin, Johnson & Johnson, Sputnik V, Novarax, and CoronaVac).

The authors found a strong link between how many antibodies people had early in the clinical vaccine trials and vaccine-efficacy results from the later stages of the trials. In other words, people who had good levels of antibodies early on, were less likely to come down with COVID-19 during the vaccine trials.

Among the vaccines that generated the strongest neutralizing antibody responses were the mRNA-based vaccines made by Moderna and Pfizer, as well as the protein subunit vaccine from Novarax. These three were also the most protective against SARS-CoV-2 infection.

Intermediate levels of neutralizing antibodies – and intermediate protection – were observed in individuals who recovered from COVID-19, or who received India’s Covaxin and Russia’s Sputnik V. Weaker, but still protective, responses were recorded for CoronaVac, Johnson & Johnson, and AstraZeneca vaccines.

The team’s model made several more interesting predictions:

  • Several variants of concern would escape protection with more ease.
  • Antibody levels would likely wane over time, making people more prone to SARS-CoV-2 infections a while after having first been infected or having been vaccinated.
  • Despite antibody waning, those previously infected or who had been vaccinated would not have a high likelihood of severe COVID-19 disease.

The authors suggest that booster shots might be needed a year after the initial vaccination.


Khoury DS, Cromer D, Reynaldi A, Schlub TE, Wheatley AK, Juno JA, Subbarao K, Kent SJ, Triccas JA and Davenport MP. Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection. Nature Med. 2021 May 17. doi: 10.1038/s41591-021-01377-8.