News
On blood-clotting incidents, vaccines and variants
With concerns rising over the alleged drop in the platelet count and blood-clotting in a few cases, the Sunday Times sought the opinion of the Head of the Department of Immunology and Molecular Medicine, University of Sri Jayewardenepura, Prof. Neelika Malavige about this and other questions on vaccines and variants.
Setting down the facts, Prof. Malavige said that reports from some European countries which have rolled out the AstraZeneca vaccine had indicated that in some vaccinated people, there had been a drop in their platelet count and formation of blood clots leading to death.
“The European Medicines Agency (EMA) has reported this extremely rare side effect in younger people (20-50 year-old group) than in older people (especially those over 60), with a female preponderance,” she said, stressing that the important thing is to assess the benefit-risk ratio of the vaccine. The exact incidence of this “very rare” side-effect is not known.
Quoting the EMA, Prof. Malavige says that it had investigated 25 cases, particularly involving rare blood clots after vaccination and ruled that AstraZeneca’s coronavirus vaccine is “safe and effective”.
However, the EMA has said that it could not rule out a link to a “small” number of “rare” and unusual blood clot cases – an assessment that opened the way for European countries to restart paused inoculation programmes, while not fully allaying fears surrounding side-effects.
Prof. Malavige said that these seem to be very rare complications resulting from the person’s immune response, rather than the vaccine. This seems to be happening 6-14 days after vaccination and not immediately.
“It is essential to have a mechanism to monitor vaccine safety and if or when severe adverse effects are reported to thoroughly investigate them, although a majority of such complaints may not be related to the vaccine,” she stressed, adding that in COVID-19, when a person gets the disease, there seems to be blood clotting too, so it is important to monitor people who may be predisposed for clotting.
In the United Kingdom (UK), even though 11 million people have been given the AstraZeneca vaccine, no such complication has been reported. This is while many of the European countries that suspended the AstraZeneca shots — including Germany, France, Italy and Spain — said that they would resume vaccination on Friday or next week as some like Sweden and Norway said they would need time to make their own scientific evaluations.
Q. How does a vaccine work?
A. The World Health Organization (WHO) has so far given emergency-use listing to the Pfizer, AstraZeneca and Johnson & Johnson vaccines against COVID-19, while Sri Lanka has done so for AstraZeneca and Sputnik V.
These vaccines fall into two groups – adenoviral vector vaccines and mRNA vaccines.
Some of the adenoviral vector vaccines include AstraZeneca (chimpanzee adenovirus vector) and Sputnik V and Johnson & Johnson (adenoviral vector).
The mRNA vaccine is the Pfizer vaccine.
When we look at the adenoviral vector vaccines, it is similar to a tool which can be used to deliver different types of items depending on the need. The delivery mechanism (tool) is the adenovirus vector, but the item being delivered can be various types of protein for the different types of vaccine.
When considering the Sputnik V, adenovirus human vaccine trials have been carried out from 2005 to 2018 for HIV but because the efficacy was less, it had not been registered. This is while between 2015 and 2018, adenovirus vector vaccines were also under clinical trials for Ebola.
The clinical trial phases are:
Pre-clinical studies –
safety studies/animal model efficacy studies
Phase 1 clinical studies –
vaccine safety and dosage assessment
Phase 2 clinical studies –
vaccines in expanded safety trials
Phase 3 clinical studies –
vaccines in large-scale efficacy trials
With regard to the AstraZeneca’s vaccine, the ‘ChAdOx1’ is the tool or mechanism which has been used in clinical trials for advanced prostate cancer between 2015 and 2017 (Phase I) and 2017 and 2020 (Phase II). As such, they have known this vaccine platform for a while.
With these platforms being known for both Sputnik V and AstraZeneca, the data on how they worked in humans have been there from then.
The item delivered has varied from the prostate cancer antigen to protein from HIV and Ebola. When the new coronavirus began spreading across the world, instead of the prostate cancer antigen or the protein from HIV or Ebola, what was substituted to be delivered through this platform or tool was the spike protein of the coronavirus.
Meanwhile, the Pfizer vaccine uses mRNA (messenger ribonucleic acid). Here a lipid envelope contains a piece of mRNA with codes for the spike protein of the coronavirus. When the vaccine is injected into a human, this lipid nano-particle goes into the muscle cell. These tiny particles of the virus or ribosome that function to synthesize proteins, have nothing to do with the person’s cell nuclei or DNA (deoxyribonucleic acid).
The spike protein is synthesized in the human cell, released to the body and results in the development of antibodies and a T-cell response (T-cells are important white blood cells of the immune system and play a central role in the adaptive immune response).
Our genome is DNA and there is no way that any vaccine can be incorporated into our DNA as it is RNA. While DNA is the hereditary material in humans and almost all other living organisms, RNA is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. The vaccines do not cause infertility or impotence.
Q. What are variants?
A. It is natural for all viruses to mutate. Around 99.9 % of the time, these mutations are insignificant. They become significant if such a mutation increases transmissibility and severe disease and escapes vaccine efficacy.
Virus mutation is due to the law of natural selection. Viruses mutate to stay longer and these are called ‘escape’ mutations because usually when a virus is there for a while, people can develop immunity. Then the virus mutates to escape the immunity developed by people and keep spreading disease.
Two of the variants which are causing worry are the South African and Brazilian variants.
However, there is good news because the vaccines that have been developed do prevent severe disease and death. The next step, therefore, is to update these vaccines to meet these new mutations.
In an mRNA or vector vaccine, what they have to do is to introduce new spike proteins of the new mutation because the fundamental vaccine is already there. They can be rapidly modified to meet the challenges being posed by the new variants and that is what is happening currently.