Alpha to Delta switch behind city’s 4th wave
- Late on Thursday, Public Health England (PHE) updated its technical analysis of the variant to say that the variant that was first found in India is more likely to lead to hospitalisations than the variant that has been predominant in the UK.
The Delta variant of Sars-Cov-2 out-competed the Alpha variant within weeks and went on to spark Delhi’s most devastating wave of Covid-19 yet, according to a new report by Indian scientists who carried out genomic analysis, providing yet more evidence that India needs to reconsider its decisions to delay second doses of the vaccine.
The report is yet to undergo peer review and was published late on Thursday by researchers from the National Centre for Disease Control (NCDC) and Institute of Genomics and Integrative Biology (IGIB).
It is part of a flurry of scientific evidence published in the last 24 hours that reinforces fears that the Delta variant, also known as B.1.617.2, is harder to contain and may be leading to more vaccine breakthrough cases and even severe disease – attributes that have implication for India’s vaccination drive, especially the decision to delay second doses.
“Although we don’t have effectiveness data for the Covishield vaccine against severe disease with the Delta variant, the UK data from PHE and from the Crick Institute point to the urgent need to review our data and our policies and use impact modeling to decide if a change is needed,” said Dr Gagandeep Kang, professor of microbiology at Christian Medical College-Vellore.
“While much more remains to be done, three takeaways for now are: Delta (B.1.617.2) is more transmissible than Alpha (B.1.1.7), there seems to be greater immune escape and reinfection, and fully vaccinated breakthroughs were disproportionately due to Delta,” said Dr Anurag Agarwal, director, IGIB, in a tweet.
Late on Thursday, Public Health England (PHE) updated its technical analysis of the variant to say that the variant that was first found in India is more likely to lead to hospitalisations than the variant that has been predominant in the UK, or the Alpha variant (also known as B.1.1.7). A previous PHE analysis on May 27 showed the efficacy of one dose against the Delta variant was significantly lower than against the other variants (see box).
On Friday, Lancet published a fresh analysis of how vaccines perform with the variants in lab tests – where antibodies from vaccinated individuals are made to react with the different variants. It showed that the neutralising capacity of antibodies from people who got two doses of the Pfizer-BioNTech vaccine was 5.8 fold lower when the Delta variant was involved, as compared to the predecessor variant that was prevalent in 2020. This was similar to the loss of neutralisation activity seen with the Gamma (or B.1.351) variant, which has been established to be significantly resistant to vaccines.
In contrast, the Alpha variant (B.1.1.7) led to only a 2.6 fold loss in neutralisation by vaccine-trained antibodies.
The authors of the Lancet study, also from the Public Health England, said that the findings back their decision to reduce the gap between two vaccine doses, which UK announced on May 15. “These data therefore suggest that the benefits of delaying the second dose, in terms of wider population coverage and increased individual NAbTs (neutralising antibody titers) after the second dose, must now be weighed against decreased efficacy in the short term, in the context of the spread of B.1.617.2 (Delta variant).
“Worldwide, our data highlight the ongoing need to increase vaccine supply to allow all countries to extend second-dose protection as quickly as possible,” they said.
Agrawal said the timing of doses was a “complex issue”. “There are some benefits, some losses. Overall an acceptable strategy if used with flexibility of giving second dose at 8 weeks in some situations and longer intervals for others,” he said.
Taken together, these findings mean the Delta variant ticks all three boxes of traits that make a variant particularly dangerous: it is more transmissible, it is more resistant, and it can lead to more serious disease.
On transmissibility, Indian researchers from NCDC and IGIB say the manner in which the Delta variant replaced the Alpha variant in Punjab “was surprising since there is no known mutation in B.1.617 lineage or in B.1.617.2 that is associated with such high transmissibility.” Punjab previously had the Alpha variant as the dominant virus.
In Delhi, the Delta variant was relatively obscure at 5% in February, at a time when the Alpha variant’s prevalence was estimated at 20% of all samples. But by mid-April, the Delta variant overtook Alpha in prevalence, and at one point in mid-April was estimated to have a prevalence rate of 65%. It was around this time the positivity rate – the proportion of samples that return positive – in Delhi jumped to over 36%.
The Indian researchers too note that the viral load of the Delta variant (B.1.617.2) appeared to be higher than the Alpha variant (B.1.1.7), “and based on data from India and UK, so does vaccination break-through rate”. They add that B.1.617.2 is “capable of creating very fast rising outbreaks with vaccination breakthroughs”.
“We would re-emphasize that prior infections, high seropositivity and partial vaccination are insufficient impediments to its spread, as seen in Delhi, and strong public health response will be needed globally for its containment,” the authors said.