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Mixing and matching of two vaccines is not only good but better than taking either jab alone: Virologist Prof. Polly Roy

London School of Hygiene & Tropical Medicine's Polly Roy on why it's important to vaccinate everyone - rich or homeless - against Covid-19, and why 'vaccination and only vaccination is the way forward'.

June 08, 2021 / 02:24 PM IST
Virologist Professor Polly Roy works at The London School of Hygiene & Tropical Medicine.

Virologist Professor Polly Roy works at The London School of Hygiene & Tropical Medicine.


Polly Roy is a professor of virology in the Department of Pathogen Molecular Biology within the Infectious and Tropical Diseases Faculty at The London School of Hygiene & Tropical Medicine.

Roy has made significant contributions to understanding the basic molecular and cell biology, atomic structure, mechanisms of virus entry, genome synthesis, RNA packagingcapsid assembly, egress and cell-to cell transmission of viruses with double-stranded RNA genome.

In a telephonic interview she talks about the efficiency of Sputnik vaccine, the need to spruce vaccination and more.

Edited excerpts:

India will soon start administering the Sputnik vaccine. How does this vaccine work and what is your opinion about it?

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COVID-19 Vaccine

Frequently Asked Questions

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How does a vaccine work?

A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

How many types of vaccines are there?

There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

What does it take to develop a vaccine of this kind?

Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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The Sputnik vaccine is very good and is well-designed. The Sputnik vaccine, Covishield vaccine and Johnson & Johnson vaccine for Covid-19 are similar as all use harmless adenoviruses to deliver a single component of the coronavirus that causes Covid-19. The component they carry is the spike protein of SARS-CoV-2, the antigen which then generates protective antibodies in the human body. Ideally, all need two doses to make high levels of antibodies to stop SARS-CoV-2 infection, although one dose appears to be enough to stop serious disease.

The Sputnik vaccine uses two different vectors, both already developed and tested separately by other companies, the first vector is called Ad26, and has been developed by Johnson & Johnson as their Covid-19 vaccine and the second vector is Ad5, developed by CanSinoBio, a Chinese company, for their vaccine. Both have been shown to be safe and efficacious. Because of the usage of two different vectors for the two doses, the Sputnik vaccine may be more effective. In the other vaccines, including Covishield, the same vector is used twice, which can result in the first shot interfering with the second in the making of antibodies.

Can we have a mix-and-match of vaccines? Why was it decided to increase the gap period between the two doses of Covishield?

As a virologist and vaccinologist, I am convinced that mixing and matching of two vaccines is not only good but better than either alone. For instance, if you have had the first dose of Covishield, you can have the second dose of any other vaccine as per their availability and convenience. The different adenoviruses will not interfere. As regards the reason behind increasing the gap between two doses of Covishield, it is to allow the immune system more time for the production of antibodies, which in turn can fight the virus with more strength.

Can someone develop fatal Covid after being injected with both the vaccine doses?

This should not happen, and if it does, it is most likely the result of some underlying condition, like the body not being able to make enough antibodies. If someone is on immunosuppressives, for example, their immune system is already compromised and Covid can cause further havoc. Certain drugs (for example, some cancer drugs) may also hamper the making of antibodies. I would say that death of a person due to Covid after two doses is rare and not to be directly related to Covid.

How long does it take for antibodies to be produced after the second dose of the vaccine? Typically, how long will the vaccine be effective against the virus?

Well, to produce a good amount of antibodies, it takes four to six weeks after the second dose. Ideally, the effect of the vaccine should last for at least six months to one year. But we do not know about this as yet although early data looks promising in that, typically for most vaccines, protection will last for at least a year.

What should be done to arrest the spread of Covid-19?

The vaccine is the key to controlling Covid. India is a diverse country and there is a lot of disparity. We must understand that even if a beggar on the street is infected, he can create a pandemic. So the only solution is vaccinating all – irrespective of power and money.  The virus does not care who you are. Moreover, variant viruses of SARS-CoV-2 which we have seen may have small differences but they can pose more risk in infected people -more transmission equals more variants. To summarise, vaccination and only vaccination is the way forward.

How can mutations be minimised? Will the vaccine be effective against the mutated virus?

Proteins are the bricks of the virus and the proteins are made of amino acids which can change due to mutations in the viral genome. This can make the virus more transmissible. Most mutations everywhere are seeing a change in the receptor binding site of the spike. A receptor-binding domain (RBD) is a key part of a virus located on its ‘spike’ protein that allows it to dock to receptors and gain entry into cells to initiate infection. To date, although the variants have shown some lesser sensitivity to the vaccine, none has totally escaped it which is encouraging for future control.  At this juncture we should  worry less about the variants and more about getting vaccine to all.

Will the third wave attack the children more?

No, there is no scientific evidence that the children will be affected specially in the third wave although as the older are prioritized for vaccination children will naturally form a bigger proportion of the immune naive population. Luckily however, they are very unlikely to experience a severe infection.

When do we see an end to this pandemic?

This all depends on how quickly a country can vaccinate its entire population. There is a need for global collaborations amongst the countries, and India needs to step up in the manufacture of more indigenous vaccines. However, the good news is that infection can be controlled, and subject to an increased vaccine roll-out, this pandemic will end, as all do.
Vanita Srivastava

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