Explained: Why AstraZeneca halted then resumed its trial, and the challenges in vaccinating the whole world

Recently drugmaker AstraZeneca paused its clinical trial of Oxford University’s Covid-19 vaccine, after one of the trial participants developed a serious adverse reaction. There was no official clarification on what kind of reaction it was, or if it had anything to do with the vaccine.

They were media reports stating that the ailment was Transverse Myelitis, a serious condition involving inflammation of the spinal cord, which can cause muscle weakness, paralysis, pain and bladder problems. In rare instances, transverse Myelitis can also be triggered by a vaccine.

Following a review by UK drug regulator MHRA and an independent safety review committee, AstraZeneca has now resumed its vaccine trials. But trials halted in India, Brazil, the US and South Africa are yet to resume. In India, Serum Institute of India (SII), which has partnered with AstraZeneca, is conducting phase 2/3 clinical trials.

There are a number of reactions that can qualify as suspected serious adverse reactions, symptoms that require hospitalisation, life-threatening illness and even death. But these are generally very rare. To be sure, vaccines cause side effects, most of which are mild, including soreness, swelling or redness at the injection site, and fever.

Reinfections Another cause of concern is a possible reinfection of Covid-19. Recently, a 33-year-old Chinese male from Hong Kong was reportedly infected by Covid for the second time during a trip to Europe, four-and-a-half months after he first tested positive for the disease.

It was found through genomic sequencing that his second infection involved a different variant of the SARS-CoV-2 virus. While the person was found to be asymptomatic during his reinfection, his case nevertheless raised questions about antibodies waning over time and the viability of a vaccine itself.

The WHO still maintains that there is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection.

But experts say the immunity induced by a vaccine is more enduring compared to that from a natural infection.

Is there enough manufacturing capacity? The biggest global challenge is insufficient vaccine production capacity to inoculate even the most vulnerable populations. In an interview with the Financial Times, Adar Poonawalla, CEO of Serum Institute of India, the world’s largest vaccine maker, warned that there will not be enough Covid-19 vaccines available for everyone in the world to be inoculated until the end of 2024, at the earliest.

He expects the world would need 15 billion Covid-19 vaccines (two doses per person) to immunise everyone. Serum Institute has been trying to raise funds to produce 1 billion doses.

Cold storage and handling

Another big challenge in an immunisation drive is storing and handling vaccines. Many vaccines are sensitive to heat. If they are exposed to temperatures outside the recommended ranges, they lose potency and may not offer any protection. Storage and handling errors can result in the loss of patient confidence when repeat doses are required. Most conventional vaccines these days are heat-stable vaccines.

For instance, Pfizer-BioNTech’s Covid-19 vaccine, which is cruising ahead in clinical trials, has one major challenge. The mRNA vaccine cannot be stored in conventional refrigerators. Instead, it requires special ultra-low-temperature freezers that can store medicines at approximately 94 degrees below zero.

Pfizer will be making a custom-built freezer called a ‘cool box’ to distribute the vaccines and the company will remotely monitor the temperature in these boxes. This will have implications on the cost of the vaccine.

It is not known what the recommended temperature range for other vaccines is, but this will certainly be an important factor in a country like India, with its high temperatures, the absence of widespread cold-storage facilities, and likely challenges in handling the vaccines.