Many countries have now started to roll out vaccination efforts to contain the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen that causes the coronavirus disease 2019 (COVID-19).
One of the candidate vaccines, the adenovirus serotype 26 (Ad26) vector-based vaccine expressing an optimized SARS-CoV-2 spike (Ad26.COV2.S) or JNJ-78436735, is now in Phase 3 of human trials.
Developed by Janssen Vaccines (Johnson & Johnson) and Beth Israel Deaconess Medical Center (BIDMC), the vaccine is a single-dose human adenovirus vector vaccine, which has shown a 66-percent efficacy against SARS-CoV-2.
A new study, conducted by researchers at the Harvard Medical School, Tufts University and the Massachusetts Institute of Technology in the U.S. and the Janssen Vaccines & Prevention BV in the Netherlands, showed that a single immunization with a low dose of the Ad26.COV2.S vaccine – also known as the ‘Johnson & Johnson vaccine’ – effectively protected against SARS-CoV-2 challenge in rhesus macaques.
The team also revealed that a higher vaccine dose might be needed to protect the upper respiratory tract compared with the lower respiratory tract.
The team’s findings have been released on the preprint bioRxiv* server.
The Ad26.COV2.S vaccine was derived from the first clinical isolate of the Wuhan strain. The Ad26 vector is used in the Ebola vaccine that was approved by the European Medicines Agency.
Ad26-based vaccines are safe and immunogenic since they are based on Janssen’s AdVac technology platform, which was also used to develop and manufacture other vaccine candidates against the Ebola virus, the human immunodeficiency virus (HIV), the respiratory syncytial virus (RSV), and the Zika virus.
In previous SARS-CoV-2 vaccine studies in nonhuman primates, the protection in the upper respiratory tract tends to be less strong than the protection in the lower respiratory tract. This means that protecting against asymptomatic infection may become more difficult to achieve than protection against severe pneumonia in humans.
However, the role of vaccine doses in the protection of the upper and lower respiratory tracts remains unclear.
In the study, the researchers assessed the immunogenicity and protective efficacy of a titration of the Ad26.COV2.S dose levels to determine if it would still be effective against SARS-CoV-2.
The researchers vaccinated 30 rhesus macaques once with various doses of the vaccine, including 1x1011, 5x1010, 1.125x1010, or 2x109 vp Ad26.COV2.S or sham and were exposed to the virus by the intranasal and intratracheal routes.
Interestingly, the research findings showed that vaccination with doses as low as 2x109 bp provided strong and potent protection in bronchoalveolar lavage. Meanwhile, doses of 1.125x1010 vp were required for protection in nasal swabs.
The team noted that low doses of the vaccine protected against SARS-CoV-2 in the lower respiratory tract. However, they also found that higher doses are needed to protect the upper respiratory tract. Also, suboptimal vaccine dose levels have led to decreased efficacy to protect against the infection, while no evidence of vaccine-associated enhanced respiratory disease (VAERD) was noted.
The researchers observed that low doses of Ad26.COV2.S protected against the virus’s challenge in the lower respiratory tract, but that higher vaccine dose levels were required to protect in the upper respiratory tract. Suboptimal vaccine dose levels resulted in reduced protective efficacy, but no evidence of VAERD was observed.
There are currently 2 phase 3 human trials in progress to determine the safety and efficacy of the vaccine against the virus in a large group of people.
If the results are promising, the vaccine may be used alongside the current candidates to prevent infection in many countries.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.