The optimal
booster vaccine schedule against COVID-19 is still being explored. The
present study aimed at assessment of the immunogenicity and antibody
persistency of inactivated-virus based vaccine, BBIP-CorV and
protein-subunit based vaccines, PastoCovac/Plus through heterologous and
homologous prime-boost vaccination. Totally, 214 individuals who were
previously primed with BBIBP-CorV vaccines were divided into three arms
on their choice as heterologous regimens BBIBP-CorV/PastoCovac (n = 68),
BBIBP-CorV/PastoCovac Plus (n = 72) and homologous BBIBP-CorV (n = 74).
PastoCovac booster recipients achieved the highest rate of anti-Spike
IgG titer rise with a fourfold rise in 50% of the group. Anti-RBD IgG
and neutralizing antibody mean rise and fold rise were almost similar
between the PastoCovac and PastoCovac Plus booster receivers. The
antibody durability results indicated that the generated antibodies were
persistent until day 180 in all three groups. Nevertheless, a higher
rate of antibody titer was seen in the heterologous regimen compared to
BBIP-CorV group. Furthermore, no serious adverse event was recorded. The
protein subunit-based booster led to a stronger humoral immune response
in comparison with the BBIP-CorV booster receivers. Both the protein
subunit boosters neutralized SARS-CoV-2 significantly more than
BBIP-CorV. Notably, PastoCovac protein subunit-based vaccine could be
successfully applied as a booster with convenient immunogenicity and
safety profile.