An mRNA vaccine may protect older patients

Good news in the race for a vaccine

A trial study published yesterday has shown encouraging results from an mRNA vaccine candidate amongst patients in the over-50’s age group – those most at risk from COVID-19.

Although there are huge number of vaccine trials being conducted worldwide, many of which have shown positive results so far, there has been some doubt about the effectiveness of some types of vaccine amongst more mature patients. Those are, of course, the people who are likely to benefit most from a vaccine.

A team of scientists led by a specialist in infectious diseases and vaccination at Emory University School of Medicine, Atlanta, Georgia, has shown that an mRNA COVID-19 vaccine candidate (mRNA-1273) has triggered a positive immune response amongst targeted groups of patients. The results were published yesterday in the New England Journal of Medicine.

Although the study is based upon low numbers of patients (it had 40 participants), it has cleared the ‘Phase 1’ threshold for success and will now move to ‘Phase 2’, which will involve significantly larger numbers of patients. Numbers of participants in Phase 1 trials have to be restricted, because it involves the greatest levels of risk.

In the study, the research team vaccinated 40 people who were stratified according to age (56 to 70 and 71 and above). All the participants were given two doses of the vaccine, with the dose increased sequentially a month after the initial dose. The trial was split into two cohorts – a low dose group (25 μg) and a high dose group (100 μg).

Although the vaccine did elicit some adverse responses (fatigue, chills, headache, muscle pain and pain at the injection site), they were all categorised as mild or moderate in severity. The adverse responses were linked to the greater doses and were more common after the second injection.

The higher does injection trigger a stronger antibody response in the patients, which supports that level of dosage as a potential candidate in another large USA-wide (‘Phase 3’) mRNA vaccine trial being led by the National Institute of Allergy and Infectious Diseases. That trial is due to be completed in November 2021.

How do mRNA vaccines work?

Ribonucleic acid (RNA) is a molecule which fulfils an essential role in our bodies in coding, decoding, regulating and expressing our genes. It’s a bit like the HTML code used to create a webpage – it instructs the body what to do and when is just about every area of our biological functions.

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.

Conventional vaccine approaches, however, are proven to provide durable and long-lasting protection, which mRNA vaccines are not. Despite their proven effectiveness, they are difficult to manufacture at scale or to develop quickly in response to a pandemic.

mRNA vaccines represent a potentially promising alternative to conventional vaccination, as they seem to offer high potency, a relative capacity for rapid development and can be produced at scale much more rapidly than conventional vaccines.

The limits of the study

The authors of the paper reporting the results do also clearly state that no correlation between the immune response that was triggered and actual protection against COVID-19 has been established.

However, the level of antibody response that was triggered has been found to correlate with protection against many other viruses.

Although it may be sometime before a candidate vaccine is proven to work and can also be manufactured at scale, the response shown amongst the ager groups of those most at risk is definitely a positive sign.