What dosage levels for the Janssen vaccine?

The Janssen vaccine is one of various COVID-19 vaccines currently available. It is based on adenovirus viral vector technology which contains DNA coding for the SARS-CoV-2 spike surface protein. This vaccine has several advantages: it requires one injection, and storage is simple. However, like the majority of vaccines on the only market, while it has proved to be effective in protecting the lower respiratory passages, it is less effective in the upper respiratory passages. This means that the virus may be able to self-replicate in the upper passages and consequently spread. The vaccine does, however, protect against severe forms of the disease.

However, it may be possible to obtain complete effectiveness by increasing the injected dose. It is for this reason that Dutch and American researchers (Janssen Vaccines & Prevention, Leiden, Netherlands, Harvard Medical School, Boston, USA) have been analysing the effectiveness of different doses of the Janssen vaccine in protecting the respiratory passageways.

The researchers immunised macaque monkeys with low doses of the vaccine (4 different doses, 5 macaques per dose). They observed production of anti-protein antibodies against the SARS-CoV-2 spike, with increased levels of neutralising antibodies associated with the 3 highest doses given. They also detected the presence of B-memory lymphocytes, though levels were minimal when the lowest dose was administered.

Regarding the protection conferred by the vaccine, the vaccinated animals were not infected by the virus in the lower respiratory passageways. However, at these dosage levels, the majority of the animals were infected in the upper respiratory tracts. The scientists observed that protection against the virus correlated with levels of neutralising antibodies and B lymphocytes: the higher the levels, the more the animal was protected.

The researchers showed that lower doses of the vaccine do protect against serious forms of COVID-19. However, higher doses were found to be necessary in order to stop the virus spreading by multiplying in the upper respiratory tracts.