Decoded: Why the Moderna Covid-19 vaccine holds promise over Pfizer's

The joke on Delhi social media is that the two new coronavirus vaccines would be unacceptable to Delhi colleges with admission cut-offs far higher than the rated effectiveness of about 95 per cent. Jokes aside, most people don’t understand what “95 per cent” (or “94.5 per cent”) means.

Nor do people outside the biomedical research circuit grasp the magnitude of creating a working vaccine for any disease, within a year. To put that in perspective, the fastest vaccine development cycle on record was four years, for mumps.

The rapid-fire development of Covid-19 vaccines is not only due to the enormous resources thrown at Covid-19; it was possible due to use of new techniques, for so-called RNA vaccine development.

How do we calculate a vaccine’s effectiveness?

Say, there’s a trial with 10,000 people. They are divided into two equal lots of 5,000 each sorted out with similar characteristics of age, health, gender, et cetera, split between the two groups. One group gets the vaccine; the other a placebo. In a double blind trial, the doctors don’t know who gets what.

Let’s say, 50 people in the placebo group contract Covid-19, and only five individuals get it in the vaccinated group. The doctors then assume (with some degree of statistical fudging) that the vaccine has been effective in protecting 45 people, who would otherwise have been infected. So they take the ratio 50:5 and claim the vaccine is about 90 per cent effective.

In this case, one of the Covid-19 vaccines — the Moderna — is in ongoing trials with two groups of 15,000-odd volunteers each. So far, 90 people in the placebo group have contracted Covid-19, while only 5 persons in the vaccinated group have contracted Covid-19. That works out to about 95 per cent effectiveness.  The other vaccine — from Pfizer — claims similar effectiveness.

Assume for everyone’s sake, those calculations and the assumptions are accurate and bad side-effects don’t crop up. These trials are ongoing, so the “effectiveness” numbers will change, maybe even for the better. We also don’t know how long the immunity lasts yet.

How long will it take?

Those vaccines (or any of the other four, or five, in development) must be produced in quantity to inject billions of people. This will take time. Vaccines are supposed to create herd immunity. As the number of immunised people increases as a per cent of the population, infection rates drop. Even a non-immunised person is less likely to contract the disease, simply since there is less chance of encountering someone who is infected.

Eventually, if the vaccination programmes gets enough mileage, the disease is eradicated. This happened with smallpox and polio (except in a few countries), and it has greatly reduced incidence of cholera and hepatitis. Indians above a certain age will recall the annual smallpox vaccination (it was itchy) and a very painful “TABC” vaccine, which immunised against two strains of typhoid, and cholera. 

How do vaccines work?

Edward Jenner created the first vaccine back in 1798. He noticed dairy workers who were often infected with cowpox, a disease that primarily targets cattle, had smallpox immunity. So he created a vaccine using biomaterials (don’t ask, it’s disgusting!) harvested from diary workers who had recovered from cowpox. This worked. The two diseases are caused by closely related viruses. The cowpox victims had antibodies that fought off smallpox.

Later scientists discovered someone injected with a weakened or dead strain of a virus would develop antibodies. Until very recently, the basics of vaccine development involved creating weak or dead strains of virus or bacteria to be injected. The body developed antibodies, which then recognised and fought off full-fledged infections.

What’s new about RNA vaccines?

The new RNA-based technology bypasses creating dead viruses. The body uses RNA — Ribonucleic Acid — to give instructions to the DNA to produce antibodies. In effect, RNA carries the coded “recipe” for antibodies. An RNA-based vaccine is based on injecting RNA with those coded instructions. It’s a much faster, much cleaner process, which works by creating RNA with desired coding in the lab.

How much will it cost and what are the other issues?

RNA is delicate. The Pfizer vaccine (more than 90 per cent effective) must be stored at minus 20 degrees Celsius. Creating cold chains to deliver this to billions is impossible in any reasonable time. However, the Moderna vaccine (also RNA based and 94.5 per cent effective) seems viable at normal refrigeration temperatures of 2-8 degrees Celsius, which makes distribution easier. Even so, this will be a herculean task. An off-the-cuff estimate that Rs 80,000 crore is required to immunise India’s 1.3 billion could well be an underestimate.