Explained: The shelf life of Covid-19 vaccines

The ministry called the allegations “false and misleading” and said they were based on “incomplete information”. He pointed out that the shelf life of Covaxin, the only vaccine given to people under the age of 18, was extended in November after proper regulatory review, and as such, those doses of the vaccine were as good as any. any other.

What led to the concerns?

The anxiety came after several people reported that batches of vaccine that were due to expire in November were being given to younger people on Monday. The government then clarified that the shelf life of these vaccines had been extended from nine months to 12 months in November itself and that there was therefore nothing wrong with these batches.

The Department of Health said vaccine shelf life is being extended by the national regulator, the Central Drugs Standard Control Organization, or CDSCO, based on a comprehensive analysis and review of study data from stability provided by vaccine manufacturers. He also pointed out that CDSCO had also previously approved the extension of Covishield’s shelf life and that nothing special had been done for Covaxin.

Why has the expiry date for Covaxin been extended?

In response to a request from Bharat Biotech, the maker of Covaxin, CDSCO approved on October 25, 2021, to extend the shelf life of this locally developed vaccine from 9 to 12 months from the date of manufacture. This approval was based on the availability of additional “stability data” that was submitted by the company to CDSCO.

With the extended shelf life, hospitals could use expired stock and avoid wasted vaccine. It is estimated that 20 crore of vaccine doses are needed to fully immunize the nearly 10 crore of people in the 15 to 18 year age group.

In a recent statement, Bharat Biotech said it has documented excellent readings of safety and immunogenicity data in children. More than 15 crore doses of Covaxin have been administered nationwide to adults since vaccination began last year.

What are the “stability” and “shelf life” of a vaccine?

Vaccines are complex mixtures of proteins, carbohydrates, fats, inactivated viruses or adjuvants, which are substances intended to enhance the immune response and subsequent clinical efficacy of the vaccine. Together, these elements contribute to the overall efficacy and safety of the vaccine.

Like other drugs, vaccines have an expiration date and shelf life determined by the manufacturer and approved by regulatory authorities. The constituents of a vaccine can deteriorate over time due to slow chemical reactions and lose effectiveness.

According to the World Health Organization (WHO), stability is the ability of a vaccine to maintain its chemical, physical, microbiological and biological properties within specified limits throughout its shelf life.

A series of tests are designed to obtain information on the stability of a vaccine in order to define its shelf life and period of use under specified packaging and storage conditions. And depending on the nature of the antigen and other components, and the manufacturing process, stability parameters are selected on a case-by-case basis, according to WHO guidelines.

Stability studies have three specific objectives, which differ throughout the lifespan of a vaccine. First, it is carried out to determine the shelf life and storage conditions. Second, stability studies monitor the stability of the vaccine during the post-licensing period, that is, when the vaccine is on the market. Third, according to WHO guidelines, stability studies are conducted to support manufacturing changes by demonstrating the comparability of products made by different processes.

How is the shelf life calculated?

Shelf life is calculated by storing the product at different temperatures for different lengths of time and then testing its effectiveness, said leading virologist Dr Shahid Jameel. By storing the particular product at different temperatures and then checking periodically for degradation of the product, an expiration date is reached.

The length of time the product is stable and effective under the specified conditions is considered to be its shelf life. There are different biochemical ways to estimate degradation, said leading immunologist Dr Vineeta Bal.

According to WHO guidelines, the shelf life of a vaccine is the period of time during which the vaccine, if stored correctly, is expected to meet specifications, as determined by stability studies on a number of batches of the product. The shelf life is used to establish the expiration date of each lot.

For vaccines, this is done by injecting into small animals (usually mice) to assess whether the ability to make antibodies decreases with time and temperature during storage, Dr Jameel said. An expiry date means that roughly beyond that date the vaccine will not increase immunity as well as it did before. It may still work, but in a sub-optimal way, he said.

“The shelf life of a vaccine reflects the length of time the vaccine retains its potency and stability at a given storage temperature and therefore its efficacy. The shelf life is used to establish the expiration date of each batch of vaccine product. The expiration dates do not affect the safety of the vaccine, but are rather related to the potency or protection offered by the vaccine, ”the WHO regional office for Africa said in a statement in May of l ‘last year.

WHO had said that any extension of the shelf life would only apply to vaccines not yet labeled and distributed. Therefore, doses that have expired or are near expiration in distribution for use will not be affected by a future shelf-life extension decision.

Is this date extension a special favor granted to Covaxin?

No. As mentioned, CDSCO extended Covishield’s shelf life from nine months to 12 months in February last year, following a similar process. The vaccine manufacturer must submit data to show that their vaccine retains stability for longer periods of time. If the controller is satisfied with the data, it may extend the expiration period.