mRNA vaccine update October 2020

More progress with mRNA vaccines

Concerns have lingered over the ChAdOX (“the Oxford”) vaccine candidate since pre-clinical trial data suggested it would be unlikely to provide complete protection. It appeared to provide good protection against lower-airway viral replication, but no evidence of a reduction of viral replication in nasal tissue was provided. That means the virus could still be transmitted between people.

That does not mean the vaccine is not useful and it is not a confirmed position, as yet. The full trial study data will be required to objectively evaluate the effectiveness of the candidate vaccine.

Better than nothing

Although the vaccine may not entirely prevent transmission of the virus, it does still have significant likely benefits. The data confirmed that the vaccine significantly reduced the severity of COVID-19 illness, which is likely to save many lives.

mRNA vaccinations

We recently highlighted a novel approach to making a COVID vaccination, the “mRNA” pathway. These vaccines may be quite potent and much quicker to produce at scale than traditional manufacturing methods.

RNA vaccines take advantage of the process that our cells use to make proteins inside the body. The mRNA vaccine is ‘coded’ for a disease-specific (in this case COVID-19) antigen. The cells in the body then make the antigen, which is in turn recognised by the immune system.

More data published recently suggests that two mRNA candidate vaccines triggered strong immune responses, with few side effects. Both candidates appear to provide good protection from lower-airway viral replication and nasal tissue viral replication. That means they may be able to offer complete protection from infection and prevent onward transmission.

The vaccine candidate we highlighted, mRNA-1273, has just been shown to neutralise the SARS-CoV-2 virus, quickly provide protection for lower airways and nasal passages and did not cause any changes to lung tissue. The results showed the case for moving the candidate into much larger human trials, which are underway in the United States.

Now Phase 1 trial results from two more mRNA vaccine candidates have shown that they also trigger strong immune responses. The trial is still ongoing and is in a fairly limited cohort of patients (195 people). The trial is placebo-controlled, observer-blinded (but not double-blind) and patients were randomised into control or candidate groups.

The vaccine dose was escalated amongst most participants over a three-week period. Results were compared to the immune response triggered by convalescent serum treatment.

Safety first

The primary goal of the trials was to prove the safety of the vaccines, not the effectiveness of the vaccinations. One candidate (BNT162b2) showed a lower incidence and severity of reactions to the vaccine, particularly amongst older patients. Both candidates showed a stronger immune response than that triggered by convalescent serum therapy.

The results showed that both candidate vaccines were safe for human use and supported the selection of the candidates for larger Phase 2 and 3 trials.

It will still take many months for any candidate vaccine to have significant amounts of objective data available to study. However, the results show that novel approaches to vaccine development may be just as effective, if not more so, than traditional approaches.