A second shot of a messengerRNA (mRNA) based coronavirus disease (Covid-19) vaccine administered to those vaccinated with first dose of the Oxford-AstraZeneca (ChAdOx1 nCoV-19) vaccine induces a strong immune response, researchers have found in two separate studies, one of which was released on Thursday .
On Thursday, the New England Journal of Medicine published the results of a study conducted at the University Hospital of Northern Sweden in CoVacc, with Umea University, Sweden, serving as trial sponsor, which showed that an AstraZeneca (ChAdOx1-S) shot followed by a Moderna (mRNA-1273) one generated more immunity than two doses of the former. The study was conducted on 88 health care workers.
The second study, published in late June in Lancet, was conducted at five university hospitals in Spain and showed the effectiveness and safety of a second dose of the Pfizer/BioNTech (BNT162b2) vaccine on those who received one dose of the AstraZeneca one. The study covered 676 individuals
The studies are important as they show the advantages of mixed vaccine regimen, something that countries could use to their advantage while planning second doses, and, so-called booster doses (a third dose) that may be required a year or so after people receive both doses.
“BNT162b2 given as a second dose in individuals prime vaccinated with ChAdOx1-S induced a robust immune response, with an acceptable and manageable reactogenicity profile,” said the study paper, which assess the immunogenicity and reactogenicity of BNT162b2 administered as second dose in participants primed with ChAdOx1-S.
{{/usCountry}}“BNT162b2 given as a second dose in individuals prime vaccinated with ChAdOx1-S induced a robust immune response, with an acceptable and manageable reactogenicity profile,” said the study paper, which assess the immunogenicity and reactogenicity of BNT162b2 administered as second dose in participants primed with ChAdOx1-S.
{{/usCountry}}In the Moderna study, researchers found antibody levels up to 125 times higher when the second dose was mRNA-1273 as compared to five times higher when it was also AstraZeneca.
“We conclude that the mRNA-1273 vaccine can efficiently stimulate the SARS-CoV-2–specific B-cell memory that has been generated by a prime dose of ChAdOx1 nCoV-19 vaccine 9 to 12 weeks earlier and that it may provide better protection against the B.1.351 variant than a ChAdOx1 nCoV-19 boost...”
Experts say it is time to think about booster doses. “We need to start thinking about this now as at some point we would need a booster dose. It would depend on how the pandemic pans out...,” said Dr Navin Kumar, head, clinical microbiology and infection control, Manipal Hospitals.