Study: Three COVID-19 Vaccine Doses May Provide Better, Longer Protection Than Two

A third COVID-19 vaccine dose has been found to offer more durable and superior protection compared with 2 doses against contracting or being hospitalized from the Omicron variant of SARS-CoV-2 infection, according to research published in PLOS Medicine.¹

“Despite being less effective against infection with Omicron than previous variants, a third mRNA COVID-19 vaccine dose offers better protection against Omicron infection than two doses and protects well against COVID-19 hospitalization,” said Mie Agermose Gram, of Statens Serum Institut, Copenhagen, Denmark, in a press release.¹

Long-term vaccine durability can impact the rates of infections and hospitalizations against COVID-19. However, there is limited evidence about the efficacy of 2 vs 3 COVID-19 vaccine doses against these risks. Researchers conducted a nationwide cohort study to better understand the durability and efficacy of 3 vaccine doses over time.¹

The study authors gathered individual-level data of uninfected Danish residents 12 years of age and older from national Danish Civil Registration System and Danish Vaccination Registry, estimating vaccine effectiveness with vaccination status as a time-varying exposure. The team adjusted for age, sex, geographic location, and comorbidities.¹

Afterwards, investigators compared the infection and hospitalization rates of 3- and 2-time vaccinated individuals to unvaccinated individuals. Overall, the third dose provided greater and longer lasting protection against hospitalizations and infection from the Omicron variant than 2 doses.¹

“Our findings indicate that a third dose is necessary to maintain protection against infection for a longer time and to ensure a high level of protection against COVID-19 hospitalization with the Omicron variant,” the authors said in the press release.¹

In a previous study, researchers at Memorial Sloan Kettering Cancer Center compared the efficacy of 3 vs 2 doses of the COVID-19 vaccine.Nearly 100% of the participants got 2 vaccines during the study, while 60% received a third.²

One researcher wrote that the “study demonstrates improved vaccine-derived protection against COVID-19 infection in 3D [third-dose] vs. 2D [two-dose] mRNA vaccinees during the Omicron surge."²

Receiving 3 doses was found to increase protection against Omicron by more than 33%. ²

Further researcher suggests that 4 COVID-19 vaccine doses offer better protection against the Omicron variant than 2 or 3 doses.² An Israel-based study compared infection rates among health care workers who had either 3 or 4 vaccine doses. The researchers found that individuals who received 3 doses had a 13% increased breakthrough infection rate^.2

The current study was limited because the data were not randomized, which might exclude more data differentiating results from the vaccinated and unvaccinated groups.¹

The authors concluded that the “continued emergence of new variants and waning vaccine durability require ongoing evaluation of vaccine effectiveness against infection and hospitalization to inform future vaccination strategies.”¹

References

1. PLOS. Three COVID-19 vaccines may provide greater protection from COVID-19 infections than two. EurekAlert! September 1, 2022. Accessed on September 2, 2022. https://www.eurekalert.org/news-releases/962637
2. Beusekom, Mary V. Studies: 3 or 4 COVID vaccine doses protective against Omicron. CIDRAP. August 3, 2022. Accessed September 2, 2022. https://www.cidrap.umn.edu/news-perspective/2022/08/studies-3-or-4-covid-vaccine-doses-protective-against-omicron