Commentary: We can't give up on developing other COVID-19 vaccine candidates now
Results from Moderna’s and Pfizer’s coronavirus vaccine candidates show why pursuing more than one option gives the world the best chance to eliminate the pandemic, say two immunology experts.
MELBOURNE: American biotech firm Moderna has released early results from its phase 3 clinical trials, announcing in a press release on Monday (Nov 17) that its COVID-19 vaccine has an efficacy of 94.5 per cent, according to an “interim analysis” by an independent data and safety monitoring board.
While this is good news, many questions remain.
We don’t yet know how long protection against the virus will last with this vaccine. We also don’t know for sure whether this vaccine is safe and effective in different types of people, such as pregnant women, the elderly, or those with a chronic illness.
Once a vaccine is deployed “in the real world”, we’ll start to understand its true effectiveness. In practice, this is likely to be different to its efficacy in highly controlled clinical trials.
Thus far, we can only say the Moderna vaccine prevents COVID-19 symptoms, as only volunteers who developed symptoms in this trial were analysed. We don’t know for sure if it can prevent infection altogether.
Vaccines that control disease symptoms, rather than stopping infectious viruses from being transmitted from person to person, are valuable.
But it is “transmission-blocking” vaccines that are most effective at rapidly reducing viral spread and have the highest chance of eliminating a pathogen from a population.
MODERNA’S CANDIDATE MAY BE EASIER TO TRANSPORT
Like Pfizer’s vaccine, Moderna’s is an mRNA vaccine.
The company is co-developing it with the National Institute of Allergy and Infectious Diseases, part of the US federal health department.
The practical advantage Moderna appears to have over Pfizer is that its temperature requirements for distribution are simpler: 4 degrees Celsius rather than -70 degrees Celsius.
Storing and transporting a vaccine at 4 degrees Celsius initially — the temperature of a household fridge — is much easier. By contrast, -70 degrees Celsius freezers may only be found at major hospitals.
For storage beyond 30 days the Moderna vaccine needs to be kept at -20 degrees Celsius, but even -20 degrees Celsius freezers can be secured more easily.
VARYING DEGREES OF EFFICACY FOR DIFFERENT AGE GROUPS
However, while both vaccines seem to induce neutralising antibodies against the SARS-CoV-2 “spike protein”, both report relatively poor induction of the other arm of the immune response: T cells that can target the virus, particularly those that can do it after the virus has hidden inside cells.
What’s more, neither vaccine has been shown to perform as well in older people compared to young adults.
As a matter of fact, early phase 1 and 2 trials of the Pfizer vaccine saw the vaccine perform half as well in older individuals for antibody production.
Moderna’s latest human trial assessing safety and the vaccine’s ability to induce immune responses, which published final results in September after peer review, showed its vaccine induced the production of a similar amount of antibodies in adults under 70 years old, compared with those over 70. This is great news.
However, the shot induced significantly fewer T cells in adults over 71, particularly the type of T cells expected to be able to kill virus infected cells.
Thus far, it’s not known whether this will result in less protection or less sustained immunity, but it is concerning this vaccine could be potentially less effective in older people.
MANY SUCCESSFUL VACCINES IDEAL
It’s great news that multiple vaccines in the pipeline are showing good results. We now have two mRNA COVID vaccines with greater than 90 per cent reported efficacy, according to early phase 3 trial results.
This opens the door to the possibility we might have many successful vaccines, and be able to tailor different vaccines to people with different needs.
There are still more than 200 COVID vaccine candidates, many of which use different processes and types of technology. Some of these will work better for different people, for example older people, pregnant women or people with chronic diseases.
For example, the “adenovirus” vaccines, of which the Oxford University vaccine is one, seems to be good at inducing T cells.
And the University of Queensland’s vaccine looks well placed to induce immune responses specifically in older people.
Tailoring different vaccines to different people will help us increase coverage and hopefully increases the likelihood we can eliminate this virus safely.
Magdalena Plebanski is Professor of Immunology, RMIT University. Vasso Apostolopoulos is Professor of Immunology and Pro Vice-Chancellor, Research Partnerships, Victoria University. This commentary first appeared in The Conversation.