How effective is vaccination against delta variant?

The author dwells upon the issues of delta variant's relentless surge, effectiveness of vaccines against delta strain, new COVID drugs in trial, and the scenario for pediatric infections.


Representational Image (Photo: Pixabay)

Just when COVID vaccines were approved for use after the indispensable clinical trials and when the world was heaving a sigh of relief and looking forward to the imminent end of the pandemic, the delta variant of SARS-2 coronavirus emerged and has since surged across the globe like a brutal juggernaut. That the delta is so amazingly powerful may be realised from a simple fact: it now accounts for 97 per cent of all new Covid cases in the US. In May 2021, it has very low officially recorded case of delta infections. The delta variant also currently accounts for over 90 per cent cases in the UK. Why is it so worrisome? First, it is much more contagious. Second, it results in much higher viral load in the infected person. Third, it has relatively shorter incubation period compared to the original coronavirus. Fourth, delta's unique characteristics have implications for contact tracing and quarantine protocols.

According to a report by Quartz India (July 27, 2021), that cites findings of Chinese scientists, people infected with the delta variant have more than 1,000 times the viral load than those infected with the original Wuhan strain. As we may realize, a higher viral load can increase the risks of more severe disease and higher COVID transmissibility. The WHO has called the delta variant as the "fastest and fittest" strain so far. Even in countries with high vaccination rates such as Israel, the UK, and the US, the variant is currently causing the cases to surge at alarming levels. The delta strain possibly replicates faster leading to higher viral load. It also has a shorter incubation period of just 4 days against 6 days for other variants. This means that delta infections may show up positive just 4 days after the suspected infection compared to 6 days for the original strain. This means that contact tracing of infections by delta variant would be much more challenging than those by other variants. Also, the quarantine protocol for a negative test taken 72 hours prior to travel may be too long a window for the delta variant and may need to be revised.

As there is as yet no specific cure for COVID-19, the only shield against delta infections would be strict enforcement of COVID-appropriate behaviour and full vaccinations of all vulnerable populations as soon as possible, for reasons cited later. Some countries are already approving third dose or on the verge of approval. So, with the delta unstoppably spreading across the globe, we mustn't be content with single shots of the majority of the population. The majority of the population must be doubly jabbed (fully vaccinated) on a war footing.

Effectiveness of vaccines against delta variant

What do we mean by vaccine effectiveness? It refers to how well a vaccine works in the real world. It's calculated with respect to particular outcomes, such as infection, symptomatic disease, hospitalizations or death. So one can talk about how well a vaccine protects us against infections or deaths or other outcomes. If a vaccine is 70 per cent effective against hospitalizations, it means that of 100 unvaccinated people admitted in hospital due to COVID infections, only 30 would have landed in hospital had they been vaccinated. The delta variant seems to be relatively more resistant to most currently used vaccines than the alpha variant first detected in Kent, England (the UK strain).

In general, COVID vaccines are most effective against the most severe outcomes, such as death, and less effective against less severe outcomes, such as asymptomatic infections. As per a report in The Guardian (June 15, 2021), quoting a Public Health Scotland study (which has been published in The Lancet journal), 2 weeks after the 2nd dose of vaccine, protection against infection was 92% for the alpha variant and 79% for the delta variant, for the Pfizer vaccine. The corresponding figures for the AstraZeneca vaccine was 73% and 60% respectively. Protection by a single dose is relatively much lower, especially against the delta variant.

According to the latest findings of Public Health England (PHE), 4 weeks after a single dose, both the Pfizer and AstraZeneca vaccines conferred about 50% protection against symptomatic infection by the alpha variant. However, for the delta variant, this protection was relatively much lower: 36% and 30% protection against symptomatic infections by delta strain, for the Pfizer and AstraZeneca vaccines respectively. This means that, of 100 people vaccinated with a single shot of AstraZeneca (CoviShield in India), about 70 face the risk of developing symptomatic infections from delta variant. For those receiving 2 vaccine doses, this figure reduces to just about 40 people (out of 100) facing the risk of catching symptomatic infections. All these findings point to the need for administering 2  doses of the vaccine to the majority of the population as soon as feasible.

The figures are much more heartening for vaccine's protection against hospital admissions. According to a study by PHE (The Guardian, June 15, 2021), the Pfizer vaccine was 94% and 96% effective against hospitalizations from delta variant, after one and two doses respectively. The corresponding figures for the AstraZeneca vaccine was 71% and 92% respectively. To reduce the risk of hospital admissions due to delta strain and decrease the burden in hospitals too, the 2nd dose of the vaccine is urgently warranted.

A Mayo Clinic study (The Quint, Aug. 13, 2021) paints an even grimmer picture of the mRNA vaccines against the delta variant. Both the Pfizer and Moderna vaccines are now showing declining effectiveness. From January to June 2021, the vaccines were around 90% effective against infections, before delta variant appeared on the scene. But the effectiveness began dipping in June and declining even more in July, as the delta variant began surging in the US. The Pfizer vaccine is now just 42% effective against infections by the delta strain. The corresponding figure for the Moderna vaccine is 76%. The current surge in new infections and breakthrough infections in the US is supposed to be due to the spread of the delta strain and declining effectiveness of the mRNA vaccines (major vaccine in the US) against this variant. There are possibly two reasons for reduction in effectiveness. First, the immunity provided by a vaccine may wane over the course of a few months. Second, variants such as delta may be partially vaccine-resistant. That's why there is now a talk of a booster dose. Israel has already began booster dose program on Aug. 1 for people over the age of 60. It has now expanded the eligible group to individuals over the age of 50. The US has also now approved booster vaccine for people with weak immune systems (immunocompromised individuals).

However, the vaccines are still effective against hospitalizations and severe disease. Both the vaccines in preventing hospitalisations by more than 75%.

New COVID drugs in trial

WHO is now testing 3 new candidate drugs for COVID-19 in its 'solidarity trials.' These three medicines-artesunate, imatinib, and infliximab-will be tested on hospitalized COVID-19 patients in 52 countries (UN News, Aug. 11, 2021). There are now more than 203 million COVID cases worldwide but we still don't have a cure for this nasty disease. Of course, for severe and critical patients, we do have some tools such as oxygen support, dexamethasone and other steroids, blood thinners and IL-6 blockers that tame the 'cytokine storm.' But the world desperately needs more effective and accessible therapeutic agents.

These 3 drugs were chosen by an independent panel of experts for their potential in reducing the risk of death. All of them are 'repurposed drugs', as they are already being used to treat other conditions. Artesunate is an antimalarial drug, imatinib is used to treat cancers including leukemia (blood cancer), and infliximab is a monoclonal antibody used to treat rheumatoid arthritis, Crohn's disease, and other inflammatory syndromes.

We may fondly hope that one or more of these drugs pass the trial soon and are soon used to save thousands of precious lives that may otherwise fall prey to the wily SARS-2 coronavirus.

Coronavirus infections in chidlren

Previously it was thought that children mostly suffer from asymptomatic or mild COVID infections; they rarely develop severe disease or die from the disease. With the global surge of the delta variant, the scenario is rapidly changing. Of late, pediatric infections are surging in several parts of the world including the US; a significant fraction of the cases are also landing in hospitals. According to a report by National Public Radio (NPR, Aug. 10, 2021), coronavirus infections among children are rapidly rising in parts of the US. This is, of course, understandable. As more and more adults get vaccinated, the virus would increasingly find kids as vulnerable hosts. Children have a poorly developed immune system and most countries still don't deploy vaccines for young kids (12 years and below). Though kids mayn't usually suffer from critical illness, if the pool of infected kids rise significantly, a fraction would definitely land in hospitals, and a small fraction may also die. In addition, those kids who recover from asymptomatic and mild infections may suffer Long COVID, just as adults do (MIS-C is one long-haul Covid syndrome in kids). The only sure way of protecting kids is to fully vaccinate the adults around the kids. Till all adults are vaccinated and till appropriate control measures are in place, it would be too risky to open schools and put our children at the risk of exposing them to the wily coronavirus.

Children now account for nearly 15% of all new cases in the US for the week ending on Aug. 6, 2021. It's still not clear if the delta strain can make kids sicker. It still appears that severe illness, hospitalizations, and deaths are rae in children. But the growing number of hospitalized children can put a serious strain in the health care system.

Some experts opine that infections in children by delta strain seem to result in unusual symptoms such as fever, sore throat, nausea and diarrhea. Some kids also exhibit other symtoms that are seen in adults e.g. cough, breathing difficulties, fatigue, headache and body aches, runny nose, loss of smell (anosmia) and ageusia (loss of taste). As and when a third wave comes, the number of vulnerable adult population would be drastically reduced. Therefore, we must on the alert about how to protect our children during the third COVID wave and enhance health care facilities for them, before the third wave hits.

Possible measures for Manipur

Manipur must initiate the following measures to squarely face a possible third COVID-19 wave:

  1. Speeding up vaccinations in a big way; aggressive vaccinations with monthly targets to cover all eligible population with first doses in the next few weeks (4-6 weeks); and targeted vaccinations of all adult population with second doses in the next 2-3 months.

  2. Regular & repeated COVID testing in hotspots.

  3. Enhancing the ratio of RT-PCT to Rapid Antigen Testing (RAT).

  4. Weekly "awareness messaging" about the pandemic to the public by a designated healthcare official.

  5. Genomic sequencing of a subset of positive cases and surveillance of the variants including the delta variant: which COVID strains are there in Manipur, where are they, and where are they moving towards.

  6. Contact tracing and government-monitored isolation of positive cases, wherever feasible.

  7. Boosting up healthcare provisions such as medical oxygen plants, tankers and cylinders; steroids, antifungal drugs, oxygen concentrators, ventilators, oximeters, masks, PPEs, sanitizers etc.

  8. Strengthening of healthcare infrastructure such as construction of new COVID hospitals.

  9. Provision of more COVID care centres (CCCs), more Covid beds and ICUs in existing hospitals

  10. Constitution of a special taskforce for the third wave; a separate taskforce for pediatric COVID is also highly recommended.

  11. Special provisions for kids such as pediatric hospitals, wards, and ICUs, pediatric oximeters, concentrators, and ventilators and strengthening of staff such as pediatricians and pediatric nurses and paramedical workers etc.

(The views expressed are personal)

First Published:Aug. 15, 2021, 1 a.m.

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