Explained: How animal serum is used to make vaccines

Mention of newborn calf serum in a recent research paper released by the Indian Council of Medical Research (ICMR) and Bharat Biotech in the development of Covaxin has invited furore from some corners.

The Union Health Ministry has stepped in to quash these fears by clarifying that calf serum was not an ingredient of the final vaccine product, but is only used for growing cells in the laboratory that aid in the development of the vaccine.

Why is calf serum used in making vaccines?

Vaccines like Bharat Biotech’s Covaxin use the dead or inactivated virus to produce a response from the body’s immune system, which still recognises parts of the inactivated virus and mounts a defence.

To get the vaccines ready for use, the virus needs to be grown in specific ways, or cultured, in laboratory conditions. Viruses need living cells with special molecules known as “growth factors” to grow properly. This is where a solution with 5-10 per cent of calf serum is used to provide these complex growth factors that mimic human cells.

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Why does it have to be from cows?

The US Food and Drug Administration’s website says cows are used often in the development of vaccines because they are large animals, easily available and rich in enzymes. Cow foetuses are especially rich in the vital growth factors, though scientists turned to newborn calves as ethical concerns over the practice grew.

Though cow serum is rich in the nutrients needed to foster cell growth, much of the reason it is commonly used in the vaccine-making process is because it is much easier to source than other animals, given large farms in the United States, Australia and New Zealand.

Is there any calf serum in the finished vaccine?

After the growth process is completed, the vero cells are washed with water and chemicals several times over to cleanse them of the newborn calf serum. The cells are then infected with the coronavirus for viral growth.

The vero cells are completely destroyed in the process of viral growth, after which the laboratory-grown virus is inactivated and purified to make the vaccine, which contains no calf serum.