Recombinant chimpanzee adenovirus vector vaccine expressing the spike protein provides effective and lasting protection against SARS-CoV-2 infection in mice.

SARS-CoV-2 infection is a global public health threat. Vaccines are considered amongst the most important tools to control the SARS-CoV-2 pandemic. As expected, deaths from SARS-CoV-2 infection have dropped dramatically with widespread vaccination. However, there are concerns over the duration of vaccine-induced protection, as well as their effectiveness against emerging variants of concern. Here, we constructed a recombinant chimpanzee adenovirus vectored vaccine expressing the full-length spike of SARS-CoV-2 (AdC68-S). Rapid and high levels of humoral and cellular immune responses were observed after immunization of C57BL/6J mice with one or two doses of AdC68-S. Notably, neutralizing antibodies were observed up to at least six months after vaccination, without substantial decline. Single or double doses AdC68-S immunization resulted in lower viral loads in lungs of mice against SARS-CoV-2 challenge both in the short term (21 days) and long-term (6 months). Histopathological examination of AdC68-S immunized mice lungs showed mild histological abnormalities after SARS-CoV-2 infection. Taken together, this study demonstrates the efficacy and durability of the AdC68-S vaccine and constitutes a promising candidate for clinical evaluation.

Longevity of immunity following COVID-19 vaccination: a comprehensive review of the currently approved vaccines.

It is unknown how long the immunity following COVID-19 vaccination lasts. The current systematic review provides a perspective on the persistence of various antibodies for available vaccines.Both the BNT162b2 and the mRNA-1273 induce the production of IgA antibodies, reflecting the possible prevention of the asymptomatic spread. The mRNA-1273 vaccine's antibodies were detectable until 6 months, followed by the AZD1222, 3 months, the Ad26.COV2.S and the BNT162b2 vaccines within 2 months.The BNT162b2 produced anti-spike IgGs 11 days after the first dose and peaked at day 21, whereas the AZD1222 induced a neutralizing effect 22 days after the first dose.These vaccines induce T-cell mediated immune responses too. Each one of the AZD1222, Ad26.COV2.S, mRNA-1273 mediates T-cell response immunity at days 14-22, 15, and 43 after the first dose, respectively. Whereas for the BNT162b1 and BNT162b2 vaccines, T-cell immunity is induced 7 days and 12 weeks after the booster dose, respectively.

Development of an Adeno-Associated Virus-Vectored SARS-CoV-2 Vaccine and Its Immunogenicity in Mice.

Owing to the outbreak of the novel coronavirus (SARS-CoV-2) worldwide at the end of 2019, the development of a SARS-CoV-2 vaccine became an urgent need. In this study, we developed a type 9 adeno-associated virus vectored vaccine candidate expressing a dimeric receptor binding domain (RBD) of the SARS-CoV-2 spike protein (S protein) and evaluated its immunogenicity in a murine model. The vaccine candidate, named AAV9-RBD virus, was constructed by inserting a signal peptide to the N-terminus of two copies of RBD, spaced by a linker, into the genome of a type 9 adeno-associated virus. In vitro assays showed that HeLa cells infected by the recombinant AAV virus expressed high levels of the recombinant RBD protein, mostly found in the cell culture supernatant. The recombinant AAV9-RBD virus was cultured and purified. The genome titer of the purified recombinant AAV9-RBD virus was determined to be 2.4 × 1013 genome copies/mL (GC/mL) by Q-PCR. Balb/c mice were immunized with the virus by intramuscular injection or nasal drip administration. Eight weeks after immunization, neutralizing antibodies against the new coronavirus pseudovirus were detected in the sera of all mice; the mean neutralizing antibody EC50 values were 517.7 ± 292.1 (n=10) and 682.8 ± 454.0 (n=10) in the intramuscular injection group and nasal drip group, respectively. The results of this study showed that the recombinant AAV9-RBD virus may be used for the development of a SARS-CoV-2 vaccine.