COVID-19 Scan for May 11, 2022

Mix-and-match mRNA COVID vaccines may offer more Omicron protectionResearchers in Singapore discovered that a Moderna COVID booster following a two-dose Pfizer vaccine series induced a stronger neutralizing antibody response against the Omicron variant in adults compared with an all-Pfizer series, according to a study today in Clinical Infectious Diseases.The randomized controlled trial included 100 healthy adults who had completed their initial vaccination series with Pfizer-BioNTech's mRNA vaccine, 6 to 9 months prior to this study.

Participants were assigned to get either a Pfizer booster or a Moderna booster in about a 1:1 ratio. The primary end point of the study was the level of neutralizing antibodies against SARS-CoV-2 wild-type and variants of concern at day 28 post-booster.Mean SARS-CoV-2 spike antibody titers were lower in the Pfizer-only group—22,382 international units per milliliter (IU/mL; 95% confidence interval [CI], 18,210 to 27,517), compared with 29,751 IU/mL in the Moderna group (95% CI, 25,281 to 35,011; P = 0.034).More significantly, the group with a Moderna booster had higher antibodies against variants of concern, including Omicron.

The median surrogate neutralizing antibody level against Omicron in the all-Pfizer group was 72.8%, compared with 84.3% in the mixed-vaccine group.Participants ages 60 and older showed a more robust immune response to mixing than younger participants, the authors said; in that group, three Pfizer doses offered 64.6% protection against Omicron, compared to 89.2% for older adults who received a Moderna third dose."For the vulnerable older age group in particular, a heterologous booster COVID-19 vaccine regimen induces a higher anti-spike antibody titer and a stronger