Boosting with an aerosolized Ad5-nCoV elicited robust immune responses in inactivated COVID-19 vaccines recipients

Introduction

The SARS-CoV-2 Omicron variant has become the dominant SARS-CoV-2 variant and exhibits immune escape to current COVID-19 vaccines, the further boosting strategies are required.

Methods

We have conducted a non-randomized, open-label and parallel-controlled phase 4 trial to evaluate the magnitude and longevity of immune responses to booster vaccination with intramuscular adenovirus vectored vaccine (Ad5-nCoV), aerosolized Ad5-nCoV, a recombinant protein subunit vaccine (ZF2001) or homologous inactivated vaccine (CoronaVac) in those who received two doses of inactivated COVID-19 vaccines.

Results

The aerosolized Ad5-nCoV induced the most robust and long-lasting neutralizing activity against Omicron variant and IFNg T-cell response among all the boosters, with a distinct mucosal immune response. SARS-CoV-2-specific mucosal IgA response was substantially generated in subjects boosted with the aerosolized Ad5-nCoV at day 14 post-vaccination. At month 6, participants boosted with the aerosolized Ad5-nCoV had remarkably higher median titer and seroconversion of the Omicron BA.4/5-specific neutralizing antibody than those who received other boosters.

Discussion

Our findings suggest that aerosolized Ad5-nCoV may provide an efficient alternative in response to the spread of the Omicron BA.4/5 variant.

Clinical trial registration

https://www.chictr.org.cn/showproj.html?proj=152729, identifier ChiCTR2200057278.

Prevalence of saliva immunoglobulin A antibodies reactive with severe acute respiratory syndrome coronavirus 2 among Japanese people unexposed to the virus

While the COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a threat to public health as the number of cases and COVID-19-related deaths are increasing worldwide, the incidence of the virus infection is extremely low in Japan compared with many other countries. To explain this uncommon phenomenon, we investigated the prevalence of naturally occurring ("natural") antibodies, focusing on those of the secretory immunoglobulin A (sIgA) form, reactive with SARS-CoV-2 among Japanese people. One hundred and eighty healthy Japanese volunteers of a wide range of age who had been considered to be unexposed to SARS-CoV-2 participated in this study. Saliva samples and blood samples were collected from all of the 180 participants and 139 adults (aged ≥ 20 years) included therein, respectively. The determination of saliva IgA antibodies, mostly comprising sIgA antibodies, as well as serum IgA and immunoglobulin G antibodies, reactive with the receptor binding domain of the SARS-CoV-2 spike-1 subunit proteins was conducted using an enzyme-linked immunosorbent assay. The major findings were that 52.78% (95% confidence interval, 45.21%-60.25%) of the individuals who had not been exposed to SARS-CoV-2 were positive for saliva IgA antibodies with a wide range of levels between 0.002 and 3.272 ng/mL, and that there may be a negative trend in positivity for the antibodies according to age. As we had expected, a frequent occurrence of assumable "natural" sIgA antibodies reactive with SARS-CoV-2 among the studied Japanese participant population was observed.