Simple and effective: with only one shot, Janssen vaccine promised to protect us against Covid-19, where the other vaccines require two doses. This asset is about to disappear: a booster shot is soon to be proposed to some patients.
The reason behind? The vaccinal booster shot campaign the French government is trying to start this Fall. After being referred to, the Haute Autorité de Santé has delivered a report: people over 65 years of age and showing comorbidities should get a booster shot to help their immune defense system with another dose of vaccine by the end of October.
In their report, released this August 24, 2021, the HAS recommends: for “people vaccinated with the Janssen vaccine, a booster shot with an mRNA vaccine (Comirnaty® or Spikevak®) is possible from 4 weeks after the first injection”.
The second dose given to people vaccinated with Janssen will be completed with mRNA vaccines, namely Pfizer or Moderna vaccines. And for good reason according to our peers from Le Monde. Several studies tend to show the use of a mRNA vaccine as a second shot to complete the first dose of an adenovirus-based vaccine "boosts the immune response" without causing adverse effects. A precious detail as no other data as for the second Janssen dose gives details as for the immune response it could induce.
The Health Minister confirmed this recommendation will be followed by the government and encouraged to people involved. According to Le Parisien, at the end of July 2021, 800,000 people in France were vaccinated with Janssen.
The Haute Autorité de Santé shares fear as for the long-term effectiveness of the Janssen vaccine, that seems less performant than the others with the variants. According to recent studies, on which the report was based, the HAS reports the Janssen vaccine is sadly “lacking in data available enabling to confirm the long-term effectiveness of Janssen’s single-jab vaccine against the Delta variant”. Yet, according to a study released this past September 2 in the New England Journal of Medicine, antibodies are still around eight months past the single-dose shot, giving an idea as for the effectiveness of the vaccine over time. Details as for the effectiveness are expected once results of phase 3 Ensemble and Ensemble 2 are released.