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COVID Boosters: The Rationale and Controversy


Lancet 9.13.21;

Study Summary

This viewpoint paper reviewed the most current data about COVID immunity, the benefits of vaccination, and the role COVID-19 vaccination boosters might play in preventing severe infection. Key findings were:

  • Humoral (antibody based) immunity (i.e., Antibody titers) reduce over time, but, even if humoral immunity appears to decrease, this reduction does not predict reductions in the vaccine’s efficacy over time.
  • Reductions in vaccine efficacy against mild disease do not predict or correlate with reductions in the efficacy against severe disease.
  • Data shows efficacy of most of the vaccines against symptomatic disease is less for the delta variant than for the alpha variant, but there remains high vaccine efficacy against both symptomatic and severe disease due to the delta variant and all of the main viral variants.
  • One rationale for this is the protection against severe disease is mediated by both antibody response and by cell-mediated immunity, whose response lasts much longer.
  • To date, none of the data has provided evidence of declining protection against severe disease, even when there were declines in vaccine efficacy against symptomatic disease over time.
  • Current vaccine supplies would likely save more lives if used in previously unvaccinated populations than if used as boosters in vaccinated populations.


Despite the decrease in antibody titers over time, all vaccines prevent serious illness and death, even from the delta variant. Adding a booster to those who are relatively low risk is unlikely to prevent serious illness, and society would be better served and have a greater reduction in illness burden by focusing on immunizing those who are currently unvaccinated.


The great news here is the primary immunization, while possibly having less effective against symptomatic illness, is still highly efficacious in preventing serious illness and death. The quandary is what to do next.

One possible approach is to offer boosters to those who have high risk co-morbidities (i.e., cardiovascular, lung, and renal disease) AND having an organized approach to vaccinating the unvaccinated. The latter is really the only way to prevent further variants from evolving, and when combined with other population measures like social distancing and masks, the only way to fully control the epidemic.

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Coronavirus Disease 2019 (COVID-19)

Contributed by Frank J. Domino, MD, September 16, 2021