United States: A recent study by researchers was done to compare the immunization of mucosal and intramuscular vaccines on airborne infection and transmission of SARS-CoV-2, performed on the Syrian hamsters, findings of which were published in Science Advances.
Need of the study
The vaccines for Covid were established in 2020. They center on the spike protein and are 75-95 percent efficacious against similar variants.
However, with subsequent mutated forms of the virus, such as the Omicron, lowered the effectiveness of the vaccines, hence the booster shots. This virus has been transmitted mainly through respiratory droplets but also through contact.
About the study
This study was conducted to assess the impact of mucosal and systemic immunization on SARS-CoV-2 transmission using Syrian hamsters.
Hamsters were immunized intranasally with chimpanzee adenoviral-vectored vaccine (ChAd-CoV-2-S) or intramuscular BNT162b2 (BioNTech and Pfizer COVID-19 vaccine residual) and then exposed to SARS-CoV-2-infected hamsters, reports news-medical.net.
For the upper and lower respiratory tract, viral titers were assessed to estimate transmission. Primary contact hamsters that were not infected were also omitted. The hamsters were randomly split into vaccination and donor/contact subgroups.
Human Vero cells with transmembrane protease serine 2 (TMPRSS2) and angiotensin-converting enzyme 2 (ACE2) were used to grow the virus for the experiment.
Swabs of the nasal washes, lungs, and nasal turbinates were obtained for virological examination using RT-q PCR and plaque assay.
Both hamsters were immunized intranasally with ChAd-CoV-2-S or intramuscularly with BNT162b2, with other controls handled with phosphate-buffered saline (PBS).
Findings of the study
For the experiment, donor hamsters were infected with 105 plaque-forming units (PFU) of the WA1/2020 D614G variant. Consequently, primary contact hamsters (C1) were exposed to the donors for 8 hours within 24 hours of infection, as reported by reports news-medical.net.
Secondary contact C2 hamsters were then challenged with the C1 hamsters for eight hours after one, two, or three days of incubation.
The virological investigation of nasal washes, nasal turbinates, and lungs proved the effectiveness of primary airborne transmission for all tested specimens, excluding one nasal wash of a C1 animal from the 48-hour incubation group.
Mucosal and systemic COVID-19 vaccines’ effectiveness in reducing airborne transmission and infection was assessed.
Syrian hamsters were vaccinated intranasally with ChAd-CoV-2-S or intramuscular with BNT162b2.
Blood samples were taken from all the treated hamsters 21 days after immunization, and phylogenetic analysis was done two weeks after exposure to SARS-CoV-2-infected donors.
Virological analysis revealed that the viral inoculums reduced ChAd-CoV-2-S immunization in hamsters’ upper and lower respiratory tracts compared to non-vaccinated hamsters.
Conversely, hamsters vaccinated with the mRNA vaccine exhibited a comparatively lower degree of decrease in the titer and RNA levels, with very few animals becoming SARS-CoV-2 negative.
Mucosal immunization seems to be more effective in offering protection against contagion by airborne infective agents and their transmission.
To determine the effect on secondary transmission, vaccinated and unvaccinated C2 hamsters were for ChAd-CoV-2-S- and mRNA-vaccinated contact one hamster 72 hours after direct exposure.
In the unvaccinated controls, secondary airborne transmission (SAT) produced high virus titers in the nasal turbinates, nasal washes, and lungs.
Conclusions
In conclusion, the ChAd-CoV-2-S nasal vaccine halted primary transmission and lung infection and arrested secondary transmission to newly vaccinated and naive hamsters.
On the other hand, broad immunization with the symmetric mRNA vaccine did not stop replication in the lungs or consecutive transmission.
Therefore, these findings prove that mucosal vaccines could effectively lower respiratory tract infections and the community spread of SARS-CoV-2 by blocking sequential transmission cycles.