Geneva: Since October 5, 2021, four notable new studies have provided evidence of COVID-19 vaccine performance after full vaccination against Variants of Concern, the World Health Organization informed here today.
A test-negative case control study from the United States of America (not yet peer reviewed) evaluated the
effectiveness of Moderna-mRNA-1273 against SARS-CoV-2 infection among members (4.6 million) of a large healthcare system in Southern California aged 18 years and older. A total of 8, 153 cases were included in the study and 5 controls were matched to each case. Vaccination with Moderna-mRNA-1273 was found to be highly effective at preventing SARS-CoV-2 infection due to Delta 14-60 days post second dose (VE: 94.1%, 95% CI: 60.5 – 96.3), but declined to 80.0% (95% CI: 70.2-86.6%) at 151-180 days post second dose. Vaccine efficacy/effectiveness (VE) against infection due to non-Delta variants showed a similar pattern with a VE against infection 14-60 days post second dose of 98.6% (97.3-99.3%) which reduced to 88.7% (73.2-95.2%) at 121-150 days. VE against hospitalization due to Delta over the entire study period (≥ 14 days post second dose) was 97.6% (92.8-99.2%). VE estimates against infection over the entire study period (≥ 14 days post second dose) were 98.4% (96.9-99.1%), 95.5% (90.9-97.8%), and 90.4% (73.9-96.5%) for Alpha, Gamma, and Mu variants, respectively.
A second study from Canada (not yet peer-reviewed) provided updated results from a previous version of the pre-print. The study evaluated VE of Pfizer BioNTech-Comirnaty, Moderna-mRNA-1273, and AstraZeneca-Vaxzevria vaccines against symptomatic disease and against hospitalization or death due to Alpha, Beta, Gamma, and Delta VOCs. All vaccines were highly effective at preventing both symptomatic disease as well as hospitalization or death or more days post final vaccination (two doses). VE against symptomatic disease was ≥ 86% for each vaccine and against each VOC. VE against hospitalization or death was ≥ 92% for each vaccine against each VOC. These estimates include a follow-up time post full vaccination of up to 28 weeks, 25 weeks, and 3 weeks for Pfizer BioNTech Comirnaty, Moderna-mRNA-1273, and AstraZeneca-Vaxzevria vaccines, respectively. Of note, VE of AstraZeneca Vaxzevria against hospitalization or death due to Beta was not reported; several VE estimates were approximated to be 100% but could not be reliably assessed due to no cases in the vaccinated group.
A third peer-reviewed study from Spain, assessed the effectiveness of Pfizer BioNTech-Comirnaty, Moderna-mRNA1273, AstraZeneca-Vaxzevria and Janssen-Ad26.COV 2.S vaccines in preventing SARS-CoV-2 infection due to Alpha and Delta variants based on the vaccine status of close contacts of index cases. Moderna-mRNA-1273, Janssen Ad26.COV 2.S Pfizer BioNTech-Comirnaty, and AstraZeneca-Vaxzevria were found to be 86% (56-95%), 77% (27-93%), 71% (61-78%), and 38% (-42-73%) effective at preventing infection among close contacts due to Alpha 14 or more days post final dose, respectively, with follow-up time since complete vaccination up to 28, 23, 31 and 16 weeks for each of the vaccines, respectively. VE against infection due to Delta was similar to Alpha for the mRNA vaccines [67% (59-74%) for Pfizer BioNTech-Comirnaty, 77% (63-85%) for Moderna-mRNA-1273]. However, VE against Delta infection was lower for Janssen-Ad26.COV2.S at 42% (18-59%) than that against Alpha, although with
very wide confidence intervals for both VE estimates. The VE of AstraZeneca-Vaxzevria against Delta was 55% (39-67%); comparison to that of Alpha is hindered due to the very small numbers with Alpha infection. This study also evaluated the VE of one dose of AstraZeneca-Vaxzevria followed by a second dose of Pfizer BioNTech-Comirnaty vaccine against infection due to Delta. VE of this heterologous regimen against Delta infection 14 or more days post second dose was 86% (45-97%), with a follow-up time up to 21 weeks post full vaccination. The lower VE estimates from this study compared to estimates from other studies can possibly be explained by the fact that close contacts of index cases face frequent exposure and are, therefore, at higher risk of becoming infected even if vaccinated.
A fourth study from Israel (not yet peer reviewed) evaluated the effectiveness of a booster dose of Pfizer BioNTech Comirnaty at preventing infection, severe disease, and death compared to two doses of the same vaccine during a time when Delta was the predominant variant37. Protection against confirmed infection was lower among individuals receiving a third booster dose relative to those who received two doses of the vaccines 5 or more months prior by a factor of 8.8-17.6 depending on age group. The rate of severe disease among individuals 60 years and older was 18.7-fold (95% CI 15.7-22.4) lower in the group who received a booster dose, as compared to the group who did not receive a booster dose, and among individuals 40-59 years old, was 22-fold (95% CI 10.3-47) lower. Among persons 60 years and older, the rate of death was lower in the group who received a booster dose by a factor of 14.7 (9.4-23.1) compared to the group who did not receive a booster dose. Follow up time post-booster ranged from 3.5 weeks for individuals 16-29 years to 8 weeks for persons 60 years and older.
– global bihari bureau
