COVID-19: How is expiration date of vaccines determined?

With no takers for the stockpiles of COVID-19 vaccines, India’s private hospitals are looking at the central government for a bailout. A majority of these doses are set to expire by March-April, according to media reports.

Private hospitals administered only 4-5 per cent of the 1.7 billion doses given in India since the vaccination drive began January 17, 2021, according to Economic Survey 2021-22.

Wasted doses are a cause for concern around the globe. Only last month, Nigeria was forced to destroy a million doses of the AstraZeneca vaccine because they were past their expiry date.  Indonesia witnessed a similar fate. Around 100 million doses were rejected in December 2021 because they were too close to their expiry date, according to UNICEF officials. 

How is the expiry date determined? Is extending the expiry date of a vaccine regular practice? Are COVID-19 vaccine expiration dates too cautious? Experts weigh in.

As the vaccine is being developed, it is stored at different temperatures for different periods of time. It is then physically characterised, based on various parameters. 

Versions of the product, stored at varying temperatures for different durations, are injected into animals to see if it raises an adequate amount of antibodies. “You essentially take fresh vaccines and stored vaccines, and compare them,” Dr Shahid Jameel, immunologist and former head of former head of the Indian SARS-CoV-2 Genomics Consortium, told Down To Earth.

Date of expiry for both Covaxin and Covishield was extended last year by the Central Drugs Standard Control Organization (CDSCO) from nine months to 12 months after manufacture, based on shelf life and stability. 

A stability test is conducted to determine “acceptable quality, effectiveness and safety for a certain period of time under certain preservation conditions” of a vaccine, according to Creative Biolabs, a leader in the vaccine analytical development sector.  This also provides data to help regulate the shelf life of a vaccine.

The World Health Organization’s regional office in Africa made a statement in May 2021: 

The shelf life of a vaccine is a reflection of how long the vaccine retains its potency and stability at a given storage temperature and therefore its effectiveness. The shelf life is used to establish the expiry date of each batch of the vaccine product. 

Expiry dates do not affect the safety of the vaccine, rather are related to the potency or amount of protection the vaccine gives, the United Nations health agency noted. 

With time, especially with increasing temperature, the potency of vaccines goes down. However, that does not mean it’s unsafe to take an expired vaccine. “If it said that shelf life is six months, it doesn't mean that the day after the six months, it becomes completely useless,” Dr Jameel explained. 

Potency doesn't drop dramatically after the expiry date, it goes down slowly, he added. “Usually, the expiry date given is half of the storage time after which it starts losing potency.” 

Expired vaccines are not particularly unsafe or dangerous if administered, but are more likely to be associated with a poor immune response, said Satyajit Rath, immunologist and visiting faculty at the Indian Institute of Science Education and Research in Pune.

Extending the expiry date of a vaccine is regular practice and has been done in the past. The national regulator — CDSCO in India — analyses data gathered by the vaccine manufacturer for potency. The body can grant permission to extend the date of expiry if it is convinced. 

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