Mix-and-match better than same-type booster vax against COVID-19

Getting a heterologous vaccine booster appears to confer a greater protection against COVID-19 than homologous booster, suggest data from a Singapore study.

In addition, the risk of severe COVID-19 illness was lower among booster recipients than those who only had two vaccine doses in the primary series, regardless of whether the booster was of a heterologous or homologous vaccine type.

“The study results support recommendations for vaccine boosters and suggest that heterologous boosting may provide greater protection against COVID-19,” said the researchers. “Heterologous boosting was associated with lower SARS-CoV-2 incidence rates than homologous boosting.”

Among participants who had received two doses of BNT162b2 for their primary series, the incidence of confirmed SARS-CoV-2 infection was lower in those who had been boosted, regardless of whether the booster was a homologous or a heterologous vaccine, compared with non-boosted individuals (incidence, 227.9 and 147.9 vs 600.4 per million person-days; incidence rate ratio [IRR], 0.272 and 0.177 for homologous- and heterologous-boosted, respectively). [JAMA 2022;doi:10.1001/jama.2022.1922]

Similar results were seen among participants who were given the mRNA-1273 vaccine as the primary series. Compared with non-boosted individuals, boosted individuals had fewer confirmed infections, with greater reduction seen in those who received a heterologous booster vs a homologous booster (100.6 per million person-days; IRR, 0.140 vs of 133.9 cases per million person-days; IRR, 0.198).

In addition, the risk of severe COVID-19 was also lower with booster vs no booster among individuals who had two doses of BNT162b2 for the primary series. Compared with non-boosted individuals (incidence, 20.5 cases per million person-days), the incidence for severe illness was 1.4 cases per million person-days with homologous booster (IRR, 0.047) and 2.3 cases per million person-days with heterologous booster (IRR, 0.078).

“Severe infections were lower among those receiving a booster after BNT162b2 as the primary series compared with non-boosted individuals, regardless of the type of booster,” observed the researchers.

The study used official data of 703,209 eligible individuals (59 percent were aged 60–69 years, by person-days; 53 percent female) that were reported to the Ministry of Health, Singapore — of which, 576,132 received boosters.

As the data were collected during early phase of the booster vaccination programme (September 15 to October 31, 2021), data from younger age groups were lacking. The small number of SARS-CoV-2 infections following mRNA-1273 vaccination and short follow-up period were among the limitations of the study. The authors also acknowledged that there might be unknown individual characteristics influencing their choice of booster that could potentially confound the analysis.

“Reports of waning antibody levels and breakthrough infections among vaccinated individuals have prompted the recommendation for vaccine boosters to prevent SARS-CoV-2 infections," the researchers noted.