MRNA boosters are most effective upon receiving Janssen vaccination

A coronavirus booster shot provides a better immune response against COVID-19 than a single vaccine dose. mRNA boosters are also the most effective upon receiving Janssen. This information has emerged from a collaborative study between several organisations, including the Leiden University Medical Centre (LUMC). Findings have been published in the New England Journal of Medicine.

Due to the circulation of new coronavirus variants, the immune system can be ‘boosted’ most efficiently by combining a single Janssen vaccination with the Pfizer and Moderna mRNA vaccines, compared to a second Janssen dose or no booster at all. Researchers expect an increased effectiveness against virus infection and transmission based on observations made in the SWITCH study – a multicentre study coordinated by Erasmus MC, which includes the LUMC, UMC Groningen and Amsterdam UMC.

Healthcare workers from various academic hospitals, who had received a single dose of the Janssen vaccine in spring of 2021, were invited to take part of the study. Participants were randomly assigned a booster with Janssen, Moderna, Pfizer or none. The study looked at the effects of combining the booster shot with different vaccines on the immune system response.

Clearing out the coronavirus

Investigators focused on the effects of booster vaccines in two particular areas of the immune system: antibodies and immune cells. Antibodies are important in preventing the coronavirus infection, and immune cells ensure the coronavirus is cleared away as soon as it enters the body. An elevation in both was observed upon receiving the booster shot with Janssen, Moderna or Pfizer. However, the increase was greater with Moderna and Pfizer than with the Janssen vaccine.

Antibody levels

Janssen was the only shot approved for single dose administration and protected 85.4% of vaccinated subjects against severe COVID-19 after 28 days. Although acceptable, antibody levels upon receiving one dose of Janssen were lower than that seen after two vaccinations with an mRNA vaccine. “Because of the emergence of coronavirus variants, it is important we highlight that an additional vaccine after Janssen is appropriate!”, says Leo Visser, Professor of Infectious Diseases and also coordinator of the SWITCH study at LUMC. Not only is “mixing” with Janssen more effective than “matching”, but it is also well tolerated.

Future research will demonstrate the added value of boosting against severe disease. Investigators note that discussions concerning the need for booster shots must take into account target groups, circulation of variants and the inequality access to vaccines worldwide. Boosting with an available vaccine is better than not boosting at all.

Basis for policy

The SWITCH study is a randomised, controlled trial that included 461 healthcare workers who had received a the Janssen vaccine in May or June of 2021. In Leiden, 80 staff members from the LUMC participated. The study served as a basis for policy-making by the Health Council and the national OMT. SWITCH was made possible thanks to a financial contribution from ZonMw.

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