Coronavirus Research Tracking - 23 June

Delta variant special edition

Given the potential exposure to the Delta variant in Wellington over the last weekend this mid-week release reposts some earlier papers on this variant, and some new ones. Much of the research is coming from the UK, where the variant is becoming dominant and there is very good surveillance and research capability.

The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.

New research

Risk assessment of Delta variant in the UK

The latest Public Health England technical briefing notes that it is too soon to compare the case fatality rate for the Delta variant with the Alpha or other variants. Evidence however does indicate that vaccinations are effective in reducing hospitalisations for those infected by the Delta variant. 

An updated risk assessment on the Delta variant has also been published by Public Health England.

Comparing vaccine efficacy

A paper uses data from published studies to estimate and compare vaccine efficacy for several vaccines. It looks at the ability to prevent infection, reduce transmission, prevent disease and death. It also compares how effective some of the vaccines, after one and two doses, are against the Alpha, Beta, Gamma and Delta variants.

The results will change as more studies are published. Some caution is required in comparing results because study designs vary. The paper has not yet been peer reviewed.

More evidence that vaccinations provide protection against Delta variant

While the Delta variant shows reduced neutralisation by sera from convalescent and vaccinated people, it does not evade immune responses. The level of reduction in neutralisation ability (2.6 to 4-fold) for Delta is lower than that seen for the Beta variant, but similar to that found for the Alpha and Gamma variants. 

The research also showed that sera from some people previously infected with the Beta or Gamma variants showed no neutralisation activity against Delta, so that there may be lower levels of immunity against Delta for those who had earlier Beta or Gamma variant infections. 

The Delta and B.1.617.1 variants show only a modest increase in binding affinity with the ACE2 receptor, compared with much stronger increases (up to 7 to 19-fold) for Alpha, Beta and Gamma and some other variants. So, the increased transmissibility of Delta appears to be due to another factor. The paper was published in Cell

Previous papers covered by the Tracker

Vaccine effectiveness

The Pfizer/BioNTech and AstraZeneca/Oxford vaccines were as effective at preventing hospitalisations for the Delta variant as for the Alpha variant, according to analyses from Public Health England. Both one and two doses the vaccines provided very good protection against severe Covid-19. This is based on an analysis of over 14,000 cases involving the Delta variant. The paper, which is very brief, has not yet been peer reviewed.

In Scotland the Delta variant has rapidly become the most common variant. It is most frequently found in younger people, and the risk of hospitalisation is about twice that as for the Alpha variant. The Pfizer/BioNTech and AstraZeneca/Oxford vaccines reduced the risks of infection and hospitalisation from the Delta variant, but not as much as for the Alpha variant. 

Good protection became evident when assessed at least 4 weeks after the first vaccine dose. The study found that the AstraZeneca vaccine may be less effective at preventing infections from the variant Delta than the Pfizer vaccine, though the nature of the study did not allow for an accurate assessment of efficacy. The paper was published in The Lancet

Sera from 20 people vaccinated with the Pfizer/BioNTech vaccine was able to neutralise several newly emerged variants. While neutralisation was lower for some of the variants, the observed levels were judged to still be effective. Variants tested were Delta, B.1.617.1 & B.1.618 (both first identified in India), and B.1.525 (first identified in Nigeria). The experiments used pseudoviruses containing only the spike protein from the SARS-CoV-2 viruses. The paper was published in Nature.

The Pfizer/BioNTech vaccine is less effective against the Delta variant. Sera from 250 people who had received one or two vaccine doses were tested on five viral strains using a live virus assay. A similar reduced level of neutralising antibody activity was found for Delta as for the Beta variant, and lower than that seen for the Alpha variant. The difference was most marked when comparing variants after one vaccine dose. The authors suggest that delaying the second dose may increase risk of infection with the Beta and Delta variants. The paper was published in The Lancet

Similar results were found in an analysis by Public Health England for incidence of symptomatic infections. While the effectiveness of a single dose of either the AstraZeneca/Oxford or Pfizer/BioNTech vaccine was lower for the Delta than the Alpha variant, after two doses the difference became smaller. The paper has not yet been peer reviewed.

Monoclonal antibodies and sera from convalescent and vaccinated people were 3- to 6-fold less potent against Delta (B.1.617.2), compared with the  Alpha (B.1.1.7) variant. This is similar to the response seen for the Beta (B.1.351) variant. The Delta variant has nine distinctive spike protein mutations. 

Two doses of the Pfizer/BioNTech vaccine provided a large boost in neutralisation activity. One dose of the AstraZeneca/Oxford vaccine did not result in a strong neutralisation response against Delta, or the Beta variant.  The paper has not yet been peer reviewed.

High levels of effectiveness against the Delta variant were seen following two doses of the AstraZeneca/Oxford or Pfizer/BioNTech vaccines. Analysis of thousands of cases in the UK found that after one dose the effectiveness was 20% lower than for the Alpha variant, but the difference after two doses was much smaller. The paper has not been peer reviewed.

The greater transmissibility of the Delta variant

The Delta variant is causing concern because it appears to be more transmissible, can cause more severe symptoms, and may be better able to avoid antibody neutralisation. It appears to be spreading quickly among younger people and the unvaccinated or partially vaccinated.

Public Health England’s 3rd June technical briefing on variants of concern described that 61% of recently sequenced cases in the UK were of the Delta variant, and the prevalence of this variant was rapidly increasing. 

The report noted that the Delta variant appears to be more transmissible than the Alpha. It calculated that the secondary attack rate (probability of a close contact becoming infected) for people who have not travelled is higher for Delta (12.4%), compared to 8.2% for Alpha.

The Delta variant spread more rapidly within households than the Alpha variant, an English study has shown. A 64% increase in the odds of household transmission was found for the Delta variant, compared to the Alpha. The study didn’t have information on household sizes, which may affect the results. The paper has not yet been peer reviewed.

The greater severity of the Delta variant

A UK risk assessment for the Delta variant (from 3 June) indicated that there may be a greater risk of hospitalisation with this variant compared with Alpha. Vaccinations do provide protection, though the effectiveness appears lower than for Alpha.

A B.1.617 variant with L452R, E484Q and P681R mutations in the spike protein shows a modest ability to avoid neutralising antibodies generated by the Pfizer/BioNTech vaccine. While lab tests indicated that the variant was less effective at infecting cells, the P681R mutation enhanced fusion between an infected cell and other cells, which may lead to increased pathogenicity. The study has not yet been peer reviewed.

A news article in the 11 May issue of Nature discusses what was known about the B.1.617 variants spreading in India at that time.

Other SMC resources