A study recently published on a pre-print server revealed that a single dose of the Oxford-AstraZeneca (ChAdOx1 nCoV-19) vaccine could elicit higher titers of neutralizing antibodies, effectively acting as a booster dose, in people who have already been infected. Prior infection is associated with the development of immunoglobulin (IgG) antibodies directed against the spike, as well as neutralizing antibody titers equivalent to or even higher than those elicited by two doses of mRNA-based vaccines.
This has led to the consideration that a single dose of vaccine is adequate for this group, and a second dose may be, in fact, more likely to induce vaccine-related side effects. The same has not been reported to any large extent with the Oxford vaccine, which is built on an adenovirus vector platform. The comparison cohorts consisted of healthcare workers with and without a history of prior COVID-19. The comparison was made between two doses of the Pfizer mRNA vaccine BNT162b2 and one dose of the Oxford-AstraZeneca vaccine. Another pair of cohorts included those who received a single dose of the Oxford vaccine after prior natural infection with SARS-CoV-2. One group was less than 11 months from the infection at the date of vaccination, while the other had been infected before this.
Two control groups included unvaccinated previously infected individuals and unvaccinated individuals without evidence of prior infection. The study shows high levels of spike-targeting IgG and neutralizing antibodies in all cases, after a single dose of the Oxford-AstraZeneca vaccine, whether the person had been previously infected with the wild-type strain or with the other variants. This also holds whether the infection occurred within or beyond 11 months before the date of vaccination. The researchers conclude that one dose of the Oxford-AstraZeneca vaccine in a previously infected recipient is an effective booster of the specific immune reaction to SARS-CoV-2 when administered 11 or more months after natural infection. The elicited antibody titer and neutralizing activity are comparable to that observed after two doses of the Pfizer vaccine.
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