Protection from Third Pfizer COVID-19 Dose Diminishes Quickly Against Omicron

A new study makes a strong case for the second Pfizer COVID-19 booster and possibly more boosters in the future. Kaiser Permanente researchers found the first booster – the third dose – of the vaccine provided strong protection initially but that significantly waned after 3 months, even for hospitalization. Here are more details.

PASADENA, CA – A booster dose of the Pfizer COVID-19 vaccine provides strong protection, as much as 80% to 90%, in the first few months against hospital admissions and emergency department visits caused by infection with the delta and omicron variants. But a new study finds that protection diminished over time even after a third dose.

“Pfizer BioNTech COVID-19 booster doses significantly improve protection against omicron, although that protection seems to wane after 3 months against emergency room visits, and even for hospitalization,” explained lead author, Sara Y. Tartof, PhD, an epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation and a faculty member of the Kaiser Permanente Bernard J. Tyson School of Medicine, both in Pasadena. “Trends in waning against delta-related outcomes were generally similar to omicron, but with higher effectiveness at each time point than those seen for omicron.”

The study published in The Lancet Respiratory Medicine suggests that additional vaccine doses are likely necessary to maintain protection.

https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(22)00101-1/fulltext#:~:text=In%20adjusted%20analyses%2C%20effectiveness%20of,longer%20after%20the%20second%20dose

To reach their conclusions, researchers analyzed 11,123 hospital admissions and emergency department visits that did not result in hospital admission for acute respiratory infection Kaiser Permanente patient records in Southern California from December 1, 2021, through February 6, 2022, when both the delta and omicron variants were circulating, were reviewed.

Based on the results, the authors reported that:

• After 2 doses of the Pfizer COVID-19 vaccine, effectiveness against omicron was 41% against hospital admission and 31% against emergency department visits at 9 months.
• After 3 doses, effectiveness against omicron-related hospitalization was 85% at less than 3 months but fell to 55% at 3 months or longer.
• Against emergency department visits that did not result in hospitalization, vaccine effectiveness of 3 doses against omicron was 77% at less than 3 months but fell to 53% at 3 months or longer.

In terms of research on the issue, the authors point out, “Generally speaking, these data suggest that two doses of the mRNA vaccine are likely to provide only limited and short-lived protection against infection caused by the omicron variant and symptomatic COVID-19, and two doses have reduced effectiveness against hospital admission due to omicron compared to that seen for previous SARS-CoV-2 variants.”

They add, “Additionally, preliminary data suggest that three doses of the mRNA vaccine provide increased but modest protection against SARS-CoV-2 infection that wanes quickly, as well as increased protection against hospital admission in the first few months. The effectiveness of a third (booster) dose of an mRNA vaccine against infection with the omicron variant or symptomatic COVID-19 has been estimated to be higher than that achieved after two doses, but with waning observed in the first few months.”

“Although the Pfizer COVID-19 protection levels against omicron after 3 doses are substantially higher than those seen after 2 doses, they are less than those observed for delta or other COVID-19 strains,” Tartof explained. “Additional doses of current, adapted, or novel COVID-19 vaccines may be needed to maintain high levels of protection against subsequent waves of COVID-19 caused by omicron or future variants with similar potential to escape protection.”