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28th June 2021
With the emergence of COVID-19 variants, there is a race to ensure that the whole adult population is vaccinated to reduce the risk of severe illness and hospitalisation. But what is the real-world effectiveness against the predominant COVID-19 variants ,was a question posed in a preliminary analysis of data from EAVE II, a Scotland-wide surveillance programme which contains data on 5.4 million people (around 99% of the Scottish population), by researchers from Public Health Scotland. In a letter to the Lancet, the researchers used this database to profile COVID-19 patients and explore the risk of hospitalisation for the virus and to estimate the effectiveness of vaccines at preventing hospital admissions. They focused on two COVID-19 variants of concern (VOC); the alpha VOC (S gene negative) and the Delta VOC (S gene positive). The analysis was based on all individuals who had a PCR test and compared the proportion of cases which were positive among individuals who had been vaccinated with those who were unvaccinated. The team defined a COVID-19 hospital admission as being within 14 days of testing positive for virus or individuals who tested positive within 2 days of hospitalisation. The period of analysis was 1 April to 6 June 2021.
Prior to the period of analysis, 44.7% of the population in Scotland had received at least one dose of a COVID-19 vaccine and 7.6% had been fully vaccinated. By the end of the study period (6 June), the proportion of adults who had received at least one vaccine dose rose to 59.4% and 39.4% had been fully vaccinated. There were 19,543 confirmed positive COVID-19 infections during the period of study, of whom 377 were admitted to hospital. In addition, 7723 (39.5%) of infections and 124 (35.5%) of hospital admissions were for the Delta VOC and 70% of infections occurred in those without any vaccination. Using regression analysis, the researchers calculated that delta VOC cases were associated with an increased risk of hospitalisation (hazard ratio, HR = 1.85, 95% CI 1.39 – 2.47) compared with the Alpha VOC. Moreover, the risk of hospitalisation increased with the number of COVID-19 relevant co-morbidities.
Among those infected with the alpha VOC, the risk of hospitalisation was significantly reduced (HR = 0.28) for vaccinated compared to unvaccinated individuals. Similarly, the risk was reduced among those infected with the delta VOC (HR = 0.38). In terms of vaccine effectiveness in the whole cohort, 14 days after being fully vaccinated with the BNT162b vaccine, there was a good level of protection against the alpha VOC although this was reduced for the delta VOC (92% vs 79%, Alpha VOC vs Delta VOC). In contrast, protection with the ChAdOx1 was lower (73% vs 60%, alpha VOC vs delta VOC).
In summarising their findings, the authors noted that the risk of hospitalisation was nearly double with the Delta VOC compared with the Alpha VOC. Moreover, while the results suggested that the BNT162b vaccine appeared to be more effective against the Delta VOC, the small number of cases meant that these results should be interpreted with caution.
Shiekh A et al. SARS-CoV-2 Delta VOC in Scotland: Demographics, Risk of Hospital Admission, and Vaccine Effectiveness. Lancet 2021
28th May 2021
COVID-19 mutations are to be expected and one particular lineage, B.1.617.2, first identified in India, has spread globally to at least 43 countries. As with all COVID-19 variants, a major concern for governments, is whether currently approved vaccines will provide sufficient protection against any such variants, especially given the fact that two recent variants, B.1.1.7 (first identified in the UK) and B.1.351 (identified in South Africa) have been shown to be resistant to sera from vaccinated individuals. Nevertheless, other data is more encouraging, suggesting that the BNT162b vaccine is effective against both variants of concern. The Indian variant of concern, B.1.617.2, has mutations in the spike protein which could potentially impact on the immune response. In a preprint study, a team from Public Health England, examined the effectiveness of two COVID-19 vaccines, BNT162b and ChAdOx1 against the variants of concern, B.1.1.7 and B.1.617.2. Data on the date of vaccinations and vaccine type were extracted from a national registry until 16th May 2021 and genomic sequencing was used to identify the proportion of different variants of concern present in positive PCR test samples.
A total of 12,675 sequenced cases were included in the analysis with 11,621 cases of B.1.1.7 and 1054 of B.1.617.2. Among individuals who had only received a single vaccine dose, overall efficacy was 33.5% against B.1.617.2 and 51.1% against cases of B.1.1.7. For the two vaccines, single vaccination with BNT162b had an efficacy of 49.2% against B.1.1.7 and only 33.2% against B.1.671.2. Similarly, the ChAdOx1 vaccine was only 51.4% effective against B.1.1.7 and 32.9% effective against B.1.671.2. However, once fully vaccinated, the overall vaccine efficacy was 86.8% against B.1.1.7 and 80.9% against B.1.617.2. The BNT162b was found to be the most effective with an efficacy of 93.4% and 87.9% against B.1.1.7 and B.1.617.2 respectively. However, while less effective, the ChAdOx1 still provided a satisfactory level of protection with a reported efficacy of 66.1% and 59.8% against B.1.1.7 and B.1.617.2 respectively.
The authors discussed how their findings indicated that only a single vaccine offered limited protection against these variants but that the efficacy was satisfactory once individuals were fully vaccinated, highlighting the importance of ensuring that all adults receive both doses.
Bernal JL, Andrews N, Gower C et al. Effectiveness of COVID-19 vaccines against B.1.617.2. variant. Public Health England 2021