Covid-19: How is a vaccine’s shelf life calculated?

The Centre recently issued a clarification following concerns that children were being administered “expired” Covaxin vaccines. The Union Health Ministry said the claims were misleading and based on incomplete information, adding that Covaxin’s shelf life had been extended following regulatory scrutiny. Covaxin is the only vaccine against Covid-19 approved for children in the 15-18 age group.

SHELF LIFE OF A VACCINE

Recently, concerns were raised after teenagers were administered Bharat Biotech’s Covaxin, which was supposed to expire in November. The Union Health Ministry, however, clarified that the Central Drugs Standards Control Organisation (CDSCO) had extended the shelf life of vaccines following comprehensive analysis and examination of stability study data provided by the manufacturers. In a similar move last year, the Trinidad and Tobago Health Ministry had extended the shelf life of the Pfizer/BioNtech vaccine from six to nine months.

STABILITY TESTS

According to the World Health Organization, a vaccine’s stability is determined by its ability to retain physical, chemical, biological, and microbiological properties within specified limits throughout its shelf life. The stability tests determine a vaccine’s storage conditions and shelf life after monitoring its stability when it is commercially marketed. These tests are conducted to support manufacturing changes by demonstrating the comparability of the vaccine manufactured through different processes.

CALCULATING SHELF LIFE

Shelf life is calculated by storing the vaccine at various temperatures for various lengths of time and then testing its effectiveness. The shelf life establishes a batch’s expiry date — meaning the date after which the dose, while working sub-optimally, won’t raise immunity. Expiry dates affect a vaccine’s potency, not safety. The World Health Organization has said any shelf-life extension would only apply to vaccines not yet labelled and distributed.

INDIA SITUATION

Manufacturers have to submit data to the CDSCO to show that its vaccines retain stability for longer periods. The regulator extends the expiry period if it is satisfied with the data. Last February, the CDSCO extended the shelf life of Covishield, produced by Serum Institute of India from nine to 12 months. Covaxin’s shelf life was extended in October.