3 vaccine doses are critical for protection against the COVID-19 Omicron variant
3 vaccine doses are critical for protection against the COVID-19 Omicron variant

3 vaccine doses are critical for protection against the COVID-19 Omicron variant

Investigators are calling for routine monitoring of vaccination effectiveness as the pandemic continues to evolve.

Three doses of an mRNA vaccine are required to achieve an equivalent level of protection against COVID-19 Omicron variant, which 2 doses give against the Alpha and Delta variants, results of a study published in BMJ showed.

In addition, the results show that although the severity of the disease among people admitted to the hospital is lower with Omicron than with Delta, the former is still at risk of critical illness and death.

The results of previous studies suggested reduced the effectiveness of the vaccine against infection and hospitalizations for Omicron compared to previous variants. However, little is known about the effectiveness of vaccines in preventing the most serious infections of COVID-19 in people taking Omicron.

Investigators aimed to address this issue and assessed the clinical severity of COVID-19 associated with the Alpha, Delta and Omicron variants among hospitalized adults and compared the efficacy of 2 and 3 doses of mRNA vaccines to prevent hospitalizations. related to variants.

The study included 11,690 adults admitted to 21 hospitals across the United States between March 2021 and January 2022. There were 5,728 people with COVID-19 and 5,962 people without COVID-19 who were used as controls.

The individuals were classified into 3 groups based on viral gene sequencing for the variant or after the dominant circulating variant at that time.

Between March 11, 2021, and July 3, 2021, the Alpha variant was the primary strain; between July 4, 2021 and December 25, 2021, it was the Delta variant; and between December 26, 2021 and January 14, 2022, it was the Omicron variant.

Vaccine efficacy was calculated for each variant and the severity of the disease was compared between the variants. Investigators used the World Health Organization’s clinical progression scale, which evaluates how seriously ill a person becomes in the hospital.

The efficacy of 2 doses of an mRNA vaccine to prevent hospitalization with COVID-19 was lower for the Omicron variant than for the Alpha and Delta variants by 65%, 85% and 85%, respectively, whereas 3 doses achieved 86% efficacy against Omicron, equivalent to 2 doses of Alpha and Delta.

Among those not vaccinated and hospitalized with COVID-19, the Delta variant was associated with the most serious disease, followed by Alpha and then Omicron.

In contrast, the Omicron variant was associated with significant critical illness and death, with 15% of people hospitalized with this variant, both unvaccinated and vaccinated, developing into invasive mechanical ventilation and 7% dying in the hospital.

In addition, vaccinated individuals admitted to the hospital with COVID-19 had a significantly lower severity of disease severity than unvaccinated individuals for all variants.

“As the COVID-19 pandemic continues to evolve, routine monitoring of vaccine efficacy, particularly against serious disease, and monitoring variants to identify viral variants will be crucial in informing booster vaccine policy decisions and vaccine strain updates,” said investigators investigating. in a statement.

The study was observational, so investigators recognized that variant error classifications could have occurred, adding that they did not take into account differences in clinical management during different variant periods.


Third vaccine dose critical for protecting populations against omicron variant. EurekAlert. News release. March 9, 2022. Visited March 10, 2022. https://www.eurekalert.org/news-releases/945612

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