AstraZeneca / Covishield vs Delta Variant, and Timing of 2nd dose of vaccine

The delta variant of SARS-COV2 is estimated to be 30-100% more transmissible than other prevalent variants and cause more severe infections than the original alpha-variant. At last count, it has spread to 80 countries and has rapidly become the dominant strain in several countries such as India and UK. Some concerns were expressed that the delta variant arose due to evolutionary pressures caused by mass vaccination. The clear answer to this is NO. The delta variant was first detected in December 2020, much before any vaccination was done in India. The strain is spreading rapidly globally as it is much more transmissible than other strains.

Breakthrough Infections in Vaccinated Persons

In April 2021, the Central Government stated that the incidence of post-vaccination COVID infections was very small at 2 to 4 per 1,000 population. However, on 17th June 2021, the Odisha government has red flagged breakthrough infections in fully vaccinated population in the state and have appointed a technical committee to look into breakthrough infections, although they have not given any numbers for their cause of concern.


Delta variant in USA

In the USA, according to the American Medical Association, over 95% of physicians have been fully vaccinated as of June 2021. COVID infections were seen in only 4.7% of fully vaccinated physicians and 63.6% of cases were in unvaccinated – a clear proof that both Pfizer and Moderna vaccines are working well against presently circulating strains in the USA. But with the Delta variant now touching 10% of fresh cases in the country and doubling every week, US President Joe Biden has expressed his apprehensions on possible rapid spread of this variant. Pfizer has claimed that their mRNA vaccine is highly effective against this variant, even though antibodies developed against the vaccine are five times lower than for the alpha variant.

UK Investigation into variants and vaccine efficacy

The UK government has released its investigation report into SARS-COV2 variants of concern, in which it is now stating that the Delta variant is the most prominent strain in the country with over 90% of fresh cases. There are some concerns in UK too, that the Delta variant may be causing breakthrough infections in fully vaccinated persons. The latest press release by the Public Health England (PHE) claims that both the Pfizer and the Oxford – AstraZeneca vaccines are highly effective against the Delta variant of SARS-COV2. The UK has vaccinated over 50% of its population fully and almost 80% with one dose. It would be reasonably accurate to consider that both vaccinated and unvaccinated persons were subject to similar risk factors and exposure. If the vaccines do not work, we should expect that the incidence of infection as well as death in vaccinated and unvaccinated population should be similar. But as per the data put out by the NIH, 12 out of 42 patients who succumbed to COVID were fully vaccinated with another nine being partially vaccinated. 23 were not vaccinated – a number almost twice as high as fully vaccinated persons. Out of 223 admissions, only 20 were fully vaccinated – a difference of around 90%.

Who has been vaccinated in the UK?

Poor Protection in First Dose

However, the protection offered against symptomatic COVID due to delta variant by a single dose of vaccination according to the same study is only 33% for AstraZeneca and 50% for Pfizer vaccine. According to the UK Government, “the difference in effectiveness between the vaccines after 2 doses may be explained by the fact that rollout of second doses of AstraZeneca was later than for the Pfizer-BioNTech vaccine, and other data on antibody profiles show it takes longer to reach maximum effectiveness with the AstraZeneca vaccine.” Clearly then, delayed administration of the second dose is resulting in delayed achievement of sufficient levels of immunity and this strategy is fraught with danger and keeps partially vaccinated people at higher risk for longer.

India’s second dose problem

As of now, only about 5% of India’s population is fully vaccinated. Partial vaccination does not offer any significant protection against the delta variant with a low efficacy of 33%. The challenge before India is to give the second dose to 20% of its massive population, and generate enough doses to administer to the remaining targeted 40% population (above 18 years). I have pointed out earlier that India’s strategy of delaying second dose seemed to be more out of compulsions related to availability than science. By next month, we will most likely have an additional two vaccines being pumped into the market and shortage would be addressed significantly. We must abandon the delayed second dose policy and revert to vaccination in 4-6 weeks as had been done earlier.

Studies from CMC Vellore as well as Fortis group have shown that vaccination was 92% – 94% effective in preventing infection and hospitalisation. A small study of just 113 healthcare workers from Fortis Hospital showed that one in seven healthcare workers tested positive despite complete vaccination but only one needed hospitalisation (incidence less than 1%). Another observational study from Apollo Indraprashtha Hospital Delhi revealed that the incidence of COVID in vaccinated healthcare workers was just 2.62% and risk of hospitalisation only 0.06%, which is quite spectacular considering the extent of destruction the pandemic caused in Delhi during the second wave. All these healthcare workers had been fully vaccinated, with most of them receiving the doses 4-6 weeks apart.

The government on the one hand claims that data from vaccination of healthcare workers clearly shows the benefits of vaccination program, but on the other hand is overlooking the fact that most healthcare workers who received their doses at 4-6 weeks interval were equally well protected as those who received delayed doses. It would be very unfair to subject a large section of the population of the country to an avoidable risk for two additional months each, given that they can be brought to fully immunized status much earlier.

A small study on Covaxin conducted by ICMR showed that the vaccine produced higher antibody response than seen in COVID recovered patients even though levels were 2 to 4 times lower in those infected by delta strain. Covaxin second dose has been administered at 4 weeks throughout and hence is unaffected by the second dose problem. Covovax although yet to receive approval and complete phase 3 trials in India has claimed 93% efficacy against “variants of concern”. Again, this vaccine too is unlikely to be affected by a “delayed second dose” controversy. The only vaccine in which this is a topic for discussion is the AstraZeneca – Covishield, and here too there is a strong case for reverting to early second dose for offering adequate protection to those who have already taken the first dose, considering the PHE study showing poor efficacy of a single dose of the vaccine against the delta variant.

My recommendation to the government therefore is to revert to early second dose vaccination for Covishield for ensuring adequate protection of our large partially vaccinated population of 20 crores plus against the delta strain, and focus efforts on bringing more manufacturers into play faster to address the issues related to adequate stock of vaccines for the remaining population.

Differing opinions are welcome as long as you keep it clean, so go for it :)