Role of Animal Serum in Vaccine Making

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    Recently, the Government issued a clarification stating that the Covaxin vaccine did not contain the serum of a newborn calf. 

     

    Background

    • Animal rights organisation People for the Ethical Treatment of Animals (PETA) has cited reports that Covaxin uses Newborn Calf Serum (NBCS) during the production stage.
    • The calves used in the extraction of this serum are taken away from their mothers shortly after birth, which traumatises and distresses both the mother and calf.
      • The Prevention of Cruelty to Animals (Slaughter House) Rules, 2001, prohibits the slaughter of pregnant animals and animals less than three months old.
    • PETA India has urged the Drugs Controller General of India to direct vaccine manufacturers to replace newborn calf serum (NBCS) with animal-free which is commercially available and chemically-defined media for the production of the COVID-19 vaccine.
      • Animal-free media could be used to grow Vero cells for virus production instead of using NBCS extracted by slaughtering calves.
    • PETA also claimed that the use of animal-derived components such as NBCS in vaccine production compromises the quality and reproducibility of research and is often associated with the risk of contamination by non-human proteins and pathogens.

     

    Government Response 

    • The Union Health Ministry stated that the final vaccine (Covaxin) “does not contain NBCS at all and the calf serum is not an ingredient of the final vaccine product.
    • The NBCS was used only for the preparation/growth of Vero cells
      •  Vero cells are used to establish cell lives which help in the production of vaccines. This technique has been used for decades in Polio, Rabies, and Influenza vaccines.
      • These Vero cells, after the growth, are washed with water, chemicals (also technically known as a buffer), many times to make them free from the newborn calf serum. Thereafter, these Vero cells are infected with coronavirus for viral growth.
      • Thereafter this grown virus is also killed (inactivated) and purified. This killed virus is then used to make the final vaccine.
    • Hence, the final vaccine (Covaxin) does not contain newborn calf serum at all and the calf serum is not an ingredient of the final vaccine product.”
    • Covaxin is highly purified to contain only the inactivated virus components by removing all other impurities.

     

    How are Viruses Cultured?

    • Vaccines like the one made by Bharat Biotech uses the disease-causing virus itself to trigger an immune response in human beings.
    • The virus is killed, or inactivated, before being used in the vaccine, and injected into the human body, but it is still able to trigger an immune response.
    • The virus needs to be grown, or cultured, in the laboratory to be used in the vaccine.
      • Scientists try to create conditions conducive for the growth of these viruses by recreating the kind of environment that exists in an infected person’s tissues. 
      • Therefore, solutions containing ‘nutrients’ act as the growth medium for the virus.
      • These nutrients, like specific sugar and salt molecules, are extracted from tissues of suitable animals like horses, cows, goats or sheep.
      • The virus grows in these nutrient-rich solutions. After that, it goes through several stages of purification that make it suitable to be used in a vaccine.
      • There is no trace of the growth medium after the entire process is over.

     

    Why are Cow Components Used in Vaccine Development? 

    • The cow components are used mainly because cows are large animals, easily available, and rich in some of the useful chemicals and enzymes.
    • Cow milk is a source of amino acids, and sugars such as galactose. Cow tallow derivatives used in vaccine manufacture include glycerol.
    • Gelatin and some amino acids come from cow bones. Cow skeletal muscle is used to prepare broths used in certain complex media. 
    • Many difficult to grow microorganisms and the cells that are used to propagate viruses require the addition of serum from blood to the growth media.
    • Synthetic serum, and other nutrients, have also been developed, but the  serum from newborn calf, which has been used in vaccine production for over 50 years, has “proven itself as an extremely effective growth supplement
    • Animal Serum in vaccines
      • The animal serum has been used in the development of vaccines in other ways as well. 
      • The use of horse serum as an antibody supplement in the diphtheria vaccine is more than 100 years old. 
        • Horses used to be injected with small doses of bacteria that caused diphtheria so that they could develop antibodies. Later, the blood of the infected animal was used to extract the antibodies and used in the vaccine.

     

    Image Courtesy: TOI

     

    Covaxin

    • It is developed by Hyderabad-based biotechnology firm Bharat Biotech in collaboration with the Indian Council of Medical Research (ICMR) and the National Institute of Virology (NIV), Pune.
    • It is the first indigenous Covid-19 vaccine to receive approval.
    • It is based on an inactivated virus platform, one of the oldest known methods to develop an inoculation.
    • This technique has been used historically for several other diseases including Hepatitis A, Influenza, Polio and Rabies.
    • It is more likely to work against newer variants of the virus, including the UK variant as it contains immunogens (epitopes) from other genes in addition to those from Spike protein.

     

    Vero cells

    • Vero cells are derived from the kidney of an African green monkey, and are one of the more commonly used mammalian continuous cell lines in microbiology, and molecular and cell biology research. 
    • This unit includes protocols for the growth and maintenance of Vero cell lines in a research laboratory setting.
    • It has also been used in many other applications, including the propagation and study of intracellular bacteria and parasites, and assessment of the effects of chemicals, toxins and other substances on mammalian cells at the molecular level.
    • For long term storage, Vero cells are kept either in liquid nitrogen or at -80°C
    • Vero cells usually take 2-3 passages to reach their regular growth rate, and this should be taken into account if planning to use the cells for experiments, infections, etc. 
    • It is important to note that Vero cells are anchorage-dependent cells and therefore cannot be grown in suspension.

                                        Image Courtesy: Researchgate

     

    Source: IE