Clinical trials, mRNA, herd immunity? - a glossary of Covid-19 vaccine terms

THE FIRST PERSON on the island of Ireland yesterday received the Pfizer/BioNTech Covid-19 vaccine.

With a number of vaccines close to being approved for use by the European Medicines Agency (EMA), it is widely expected Ireland’s vaccination programme will be rolled out from January. 

The Government has announced its allocation strategy, publishing a list of groups in order of priority. Care home residents over the age of 65 and staff at these facilities will receive the vaccine first.

So, here’s a breakdown of some of the commonly used terms related to Covid-19 vaccines, and what they mean. 

Coronavirus

There’s a reason we knew it first as coronavirus, before we knew it as Covid-19.

Coronaviruses are a large family of viruses that can cause illnesses in humans and animals. In humans, many of them cause respiratory infections ranging from the common cold to more severe conditions such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Symptoms (SARS).

SARS-CoV-2 is the most recently discovered coronavirus.

Covid-19

As mentioned above, Covid-19 is an infectious disease and the most recently discovered form of coronavirus. It was unknown before the outbreak in Wuhan in China in December 2019.

Vaccine

Vaccines are manufactured in different ways using part of the germ or virus which causes the disease.

It is a substance that prompts the body’s immune system to recognise a particular pathogen – like a virus – and create antibodies to destroy it. If vaccinated, it means you are then in a much better position to combat the virus if you later become infected. 

Vaccination/Inoculation 

This is simply the process of administering a vaccine to the body. This is typically done through injection, as is the case with the Pfizer/BioNTech Covid-19 vaccine.

Clinical Trial

Before a vaccine is approved for use, its efficacy must first be tested in a clinical trial which observes the health outcomes of people who are given a dose of a vaccine and people who take a placebo.

Researchers also use clinical trials to see whether a vaccine causes problematic side effects.

Phase 1

The first phase of a clinical vaccine trial generally involves between 20 and 100 volunteers and the intention is to establish whether the vaccine is safe, whether it seems to work and whether there are any serious side effects. This phase will also look at how the size of the dose may be related to side effects.

Phase 2

The second phase involves several hundred people and aims to establish the most common short-term side effects and how the immune systems of those who have been given the vaccine respond. 

Phase 3

This is the most crucial and the most thorough. It involves hundreds of thousands of people, some of whom will be given a placebo.

This phase examines how people who get the vaccine compared with those who get the placebo, whether it is safe and/or effective and it also aims to catch less common side effects as it involves a larger – and ideally more diverse – pool of people. 

The results of the the trials go straight to regulators for examination after Phase Three and if the vaccine is approved based on the results, it can begin to be manufactured and administered. 

In the case of several Covid-19 vaccines these have already been manufactured, with Pfizer/BioNTech the first one to be approved for use. 

Margaret Keenan, 90, is the first patient in the United Kingdom to receive the Pfizer/BioNtech covid-19 vaccine at University Hospital, Coventry. PA PA

Emergency Use Authorisation 

The UK used this mechanism to speed up its roll-out of the Pfizer/BioNTech vaccine by applying through its Medicines and Healthcare products Regulatory Agency (MHRA).

It basically means approval can be sought and green-lighted much quicker and, given the scale and severity of the pandemic, countries are keen to see effective vaccines administered. 

Pfizer/BioNTech also applied to US Food and Drug Administration (FDA) in the United States for emergency use. The FDA is due to meet on Thursday to consider approving the application.

Ireland and the EU, meanwhile, are waiting for the European Medicines Agency (EMA) to meet on 29 December. The EMA is due to decide if both the Pfizer/BioNTech vaccine and the Moderna vaccine should be approved for use. 

The EMA has insisted it has the “most appropriate” method to approve a Covid-19 vaccines after the UK fast-tracked its process. 

Immunity 

This is the body’s ability to fight off an infection, often with the help of antibodies.

Active immunity means that antibodies are generated through exposure to a pathogen or a vaccine. 

Immunisation

This is the process of making a person – or millions of people – immune to a disease. It’s essentially the goal of vaccination.  

Herd Immunity 

This means that enough people have become immune to a disease that it makes it difficult to spread. 

In the case of Covid-19, scientists estimate that about 70% of the population will need to be vaccinated to achieve herd immunity.

In the early days of the pandemic, there were calls from some quarters to achieve herd immunity to the virus without any a vaccine having been developed. 

Chief Medical Officer Dr Tony Holohan said in October that said the application of herd immunity as a “serious health policy” in relation to Covid-19 “has no substance”. 

“Herd immunity is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached,” he said.

mRNA

The Pfizer/BioNTech vaccine is known as a messenger RNA (mRNA) vaccine.

Conventional vaccines are produced using weakened forms of the virus, but mRNAs use only the virus’s genetic code.

An mRNA vaccine is injected into the body where it enters cells and tells them to create antigens.

These antigens are recognised by the immune system and prepare it to fight coronavirus.

No actual virus is needed to create an mRNA vaccine. This means the rate at which it can be produced is dramatically accelerated.  

As a result, mRNA vaccines have been hailed as potentially offering a rapid solution to new outbreaks of infectious diseases.

In theory, they can also be modified reasonably quickly if, for example, a virus develops mutations and begins to change.

mRNA vaccines are also cheaper to produce than traditional vaccines, although both will play an important role in tackling Covid-19.

One downside to mRNA vaccines is that they need to be stored at ultra-cold temperatures and can’t transported easily.

Cold storage 

For temperatures as cold as the Pfizer/BioNTech vaccination requires, dry ice has to be brought into the mix. Currently, the vaccine is shipped in coolers that can be fed with dry ice to keep it frozen for 15 days. After this it can be refrigerated for up to five days before being diluted and injected.

The medical community is already well familiar with the use of the ‘cold chain’ for vaccinations such as flu, but GPs and pharmacists, who will likely play a significant role in the vaccination programme, do not have this kind of infrastructure.

Ireland last week received a shipment of nine cold storage freezers which will be used early next year as the vaccine is rolled out.