Mix-and-match mRNA COVID vaccines may offer more Omicron protection
Researchers 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 neutralizing antibody response against the highly infectious Omicron variant (~20% higher neutralization) than a homologous booster regimen," the authors concluded.
May 11 Clin Infect Dis study
Kids' odds of spreading COVID-19 in households rising with new variants
A systematic review and meta-analysis published today in the International Journal of Infectious Diseases suggests that while children account for less household COVID-19 transmission, their infectiousness appears to be on the rise as new SARS-CoV-2 variants emerge.
Researchers from the National Clinical Research Center for Child Health and Disorders in China led the study, which involved searching the PubMed and EMBASE databases from inception to Apr 20, 2022. Forty-eight studies were included for meta-analysis, and 47 were chosen for case analysis.
The pooled secondary attack rate (SAR) of pediatric index patients and household members was 0.20 (95% confidence interval [CI], 0.15 to 0.26) and 0.24 (95% CI, 0.18 to 0.30), respectively, in the meta-analysis. SAR refers to the likelihood of transmission to another person.
Child index cases had a 36% lower COVID-19 transmissibility risk than adults, and child contacts had a 26% lower risk (relative risk [RR], 0.64; 95% CI, 0.50 to 0.81 and RR, 0.74; 95% CI, 0.64 to 0.85, respectively). Younger and older children were equally vulnerable to infection (RR, 0.89; 95% CI, 0.72 to 1.10).
Increased household SAR was seen in children throughout different variant periods (wild-type virus, 0.20; Alpha, 0.42; Delta, 0.35; and Omicron, 0.56). The estimated SAR of adult household contacts was 0.32 (95% CI, 0.27 to 0.37) in 41 studies.
Older adults were significantly tied to a higher SAR than younger adults (RR, 1.45; 95% CI, 1.24 to 1.70 for adults younger than 60; RR, 1.24; 95% CI, 1.02 to 1.50 for older adults).
In the case analysis, 10.3% of 78 family clusters were associated with an infected child, leading to 7.7% of 207 secondary cases, versus 92.3% of those linked with an infected adult. Pediatric infections were implicated in 29.8% of 282 household contacts and 60.3% of 78 family clusters. Secondary infections spread by children made up 30% of 207 secondary infections, compared with 70% for adults.
"Given the potentially serious complications of pediatric COVID-19, vaccination research and implementation in children remain a must," the researchers concluded.
May 10 Int J Infect Dis study