An additional booster dose of mRNA vaccination in health workers has certain short-term benefits: WHO

The World Health Organization (WHO) has said that giving an extra booster dose of the mRNA COVID-19 vaccination to high-risk groups, such as health workers, those over 60, and people with immunocompromising illnesses, is beneficial.

The WHO, with the support of the Strategic Advisory Group of Experts (SAGE) on immunization and its COVID-19 Vaccines Working Group, recommended a 4-6-month delay for a first booster after completion of the first series of the vaccine, notably in the case of Omicron.

Two main scenarios to evaluate when considering additional booster doses

According to the WHO, the two main scenarios to evaluate when considering additional booster doses are the use of additional doses in those who are unable to mount and sustain adequate immune responses, and considerations for additional booster doses to be administered in order to protect high-risk populations and health workers in order to keep the health system running during periodic waves of disease surges.

Available data for WHO EUL COVID-19 vaccine products reveal that vaccine efficacy and immunogenicity are lower in immunocompromised people (ICPs) than in people without immunocompromising diseases, according to the report.

“In some ICPs, an additional dosage incorporated in an extended primary series improves immune responses. Given the significant risk of severe COVID-19 infection in ICPs, WHO has already recommended that all COVID-19 vaccines include an extended primary series (i.e. third dose) as well as a booster dose (i.e. fourth dose) for ICPs,” it stated.

Some nations are presently offering additional booster doses beyond the initial booster dosage, according to the WHO, although data on additional booster doses is only available for mRNA vaccines as of May 2022, not for other vaccine platforms.

The WHO listed seven studies that assessed the relative effectiveness of a fourth dosage four months following a third dose of mRNA vaccine versus individuals who had three doses during a time when Omicron was the most common circulating strain globally.

The WHO stated, “Taken together, these studies demonstrate some short-term benefit of an extra booster dose of mRNA vaccine among health workers, people over 60 years of age, or those with immunocompromising diseases.”

It stated that there is insufficient evidence to justify an increased dose for healthy younger populations; preliminary research suggests that the advantage is low in younger people.

“The limited available data suggest that there is a benefit that supports the administration of an additional booster dose for highest risk groups,” the WHO said, adding that in those most at risk for severe disease or death (i.e. adults over 60 years old, or those who are unable to mount a full immune response), the additional benefit of an additional mRNA vaccine booster dose might be “warranted.”

While seasonality for SARS-COV-2 has not been fully confirmed, evidence from the prior two years supports the hypothesis of greater transmission during the winter season. 

“As a result, preparations for a catch-up to increase primary series coverage and boosting for those at highest risk should take seasonality into account for countries with either a Northern or Southern Hemisphere winter season,” the WHO noted. 

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