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The use of messenger RNA (mRNA) in medical interventions has been researched for the last 20 years, including in vaccines hoping to fight diseases such as cancer, rabies, Ebola and Zika fever, which means the research technology was ready to be applied to this new disease, COVID-19. With the authorisation of two mRNA vaccines for emergency use to fight COVID-19 and more vaccine candidates in development, we can build protection against the virus in our communities if enough people are vaccinated.

What is COVID-19?

Coronaviruses are a family of viruses that cause a number of different diseases, including COVID-19. Coronaviruses get their name because of the shape of the viruses, which have spiky proteins that resemble a crown. In Latin, “corona” means crown. This unique shape allows the virus to attach itself to the cells in our eyes, mouth, nose and throat and immediately start to multiply.

COVID-19 is an infectious disease caused by a strain of coronavirus discovered in 2019, called SARS-CoV-2. 

The disease is typically spread through respiratory droplets in the air from an infected person. SARS-CoV-2 causes a range of symptoms from none at all to severe symptoms, including fever, cough, fatigue and breathing difficulty.

The COVID-19 outbreak is defined as a pandemic, because it has spread across multiple countries and has affected a large number of people, whereas an epidemic is when a disease outbreak occurs in a specific geographic area.

mRNA and how it works in a vaccine

Messenger RNA, or mRNA, are molecules within the body that contain genetic instructions for cells to make proteins that are required for the body to function properly. Unlike conventional vaccines, mRNA vaccines do not use a weakened or killed virus. Instead, mRNA vaccines deliver synthetic mRNA molecules into cells, instructing them to make antigens.
An antigen is a foreign invader that the immune system recognises as not being part of itself, such as the protein surface of a virus. In the case of the COVID-19 mRNA vaccines, cells are instructed to only make the SARS-CoV-2 spike protein, which is enough to activate the immune system. The cells are not given enough instructions to make a full virus, so the vaccine cannot cause COVID-19.
The generated SARS-CoV-2 spike protein serves as an antigen that triggers the immune system to produce specific protective antibodies that neutralise the virus - in this case, the antibodies needed to fight COVID-19. As a result, if a person is subsequently exposed to COVID-19, the immune system will already be trained to detect the antigens and produce antibodies to attack them. A vaccinated person’s immune system can better defend against the infection altogether or greatly reduce the severity of the infection.

How many doses of the mRNA vaccine are required?

The two mRNA vaccines for COVID-19 that have received conditional marketing authorisation in Europe require two doses, several weeks apart, to be effective. With these vaccines, if the body only encounters the antigen once, it’s unclear how long the protection would last. Encountering the same antigen again in a short time boosts the abundance of protective antibodies on standby, so people are safeguarded for as long as possible.

Like many vaccines for other common diseases, people may need to get vaccinated for COVID-19 again in the future. The frequency would depend on a variety of factors, including what proportion of the population receives the vaccine and how long the body retains the antibodies. Researchers are still learning how long these mRNA vaccines may provide protection in the longer term.

How does a vaccine help build herd immunity?

For many years, vaccines have been preventing illness, saving countless lives, and have greatly reduced or eliminated several diseases around the world. Advancements in vaccines are some of the greatest public health achievements over the last century. The only way we can build enough protection in our communities is if the majority of people receive the vaccine.

It's important to note that vaccinations and herd immunity are not two separate approaches to fighting a pandemic. Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. Vaccines are used to help populations reach herd immunity faster.

Do I still need to get vaccinated if I have already had COVID-19?

Yes. The European Centre for Disease Prevention and Control (ECDC) recommends being vaccinated even if you have already had COVID-19, because you can get infected more than once. You may have short-term antibodies for protection after recovering from COVID-19, but we don’t know for how long this protection will last. In addition, there were no concerns reported from the clinical trials if a participant had COVID-19 and was also vaccinated.

Are there certain people who should not receive the vaccine?

Very few, but individuals with a known history of severe allergic reaction (e.g. anaphylaxis) to any component of the COVID-19 vaccine should not receive the vaccine. In addition, consider speaking with your doctor to make the decision if:

  • You are immunocompromised, meaning you have a known impaired immune system

  • You are pregnant or breastfeeding

  • You have a history of severe allergic reaction such as anaphylaxis to any vaccine or injectable therapy

  • You are currently a participant in a gene therapy clinical trial 

The vaccine is currently not being given to children under the age of 16, but with more paediatric clinical trial data, it may eventually be available to younger ages.

If I have a rare disease, will the vaccine affect my eligibility to receive gene therapy in the future?

If you are immunocompromised, speak with your health provider to make the decision about getting vaccinated. However, there is no use of a virus or viral vector with the mRNA vaccines, so receiving an mRNA vaccine will not prevent you from obtaining a gene therapy in the future for your rare disease.

If I am currently a participant in a gene therapy clinical trial can I get the vaccine?

Check with the health provider for the gene therapy trial for confirmation before receiving the vaccine.

Will the vaccine stop me from spreading the virus to others?

At this time, there is no evidence for whether the vaccine prevents transmission of SARS-CoV-2 from person to person. Clinical trials data shows that these adenovirus-based vaccines do a very good job at preventing symptomatic COVID-19, but data is still being collected to understand how well the vaccine prevents asymptomatic infections. Research is ongoing to determine whether a vaccinated person might still be able to transmit COVID-19 to someone else who is not vaccinated. This is why it is important for a large proportion of the population to be vaccinated.

How does a vaccine help to build herd immunity?    

Vaccinations and herd immunity are not two separate approaches to fighting a pandemic. Herd immunity occurs when a large proportion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. Vaccines are used to help populations reach herd immunity faster and without spreading illness. Advancements in vaccines are some of the greatest public health achievements over the last century. The only way we can build enough protection against the virus in our communities is if the majority of people receive the vaccine.

How was the mRNA vaccine produced and tested so quickly? 

The mRNA vaccines for COVID-19 have been developed at a record-breaking speed, but that doesn’t mean that they aren’t tested to the same safety and efficacy standards as other medical interventions. Before it is made widely available, any vaccine needs to be first studied in clinical trials and then reviewed and authorised by an agency that oversees the safety and effectiveness of medical products. In Europe, this is done by the European Medicines Agency (EMA).
Starting a clinical trial for any medical intervention requires a research team, adequate funding and resources and enough initial patients and data to properly plan the study. It’s a daunting task and is often why research and development take so long. Because this disease is a global health emergency, funding has been quickly directed toward reducing many of these barriers. The goal is to treat this dangerous disease as soon as possible and, as COVID-19 infection rates increased in 2020, researchers were able to accumulate a wealth of data and eager volunteers for clinical trials. In addition, under the exceptional circumstances of the pandemic, a “rolling review” process has been applied to review drugs intended to prevent or treat COVID-19.
A rolling review is a regulatory tool that EMA uses to speed up the assessment of a promising medicine during a public health emergency. Normally, all data on a medicine or vaccine’s effectiveness, safety and quality and all required documents must be ready at the start of the evaluation in a formal application for marketing authorisation. In the case of a rolling review, EMA’s human medicines committee (CHMP) reviews data as they become available from ongoing studies. Once the CHMP decides that sufficient data are available, the company can submit a formal application. By reviewing the data as they become available, the CHMP can come to an opinion on the medicine’s authorisation sooner.
During the rolling review, and throughout the pandemic, EMA and its scientific committees are supported by the COVID-19 EMA pandemic task force (COVID-ETF). This group brings together experts from across the European medicines regulatory network to advise on the development, authorisation and safety monitoring of medicines and vaccines for COVID-19 and facilitate quick and coordinated regulatory action.

How effective are the mRNA vaccines?

Based on clinical trials, researchers and health experts have found the results to be positive. The mRNA vaccines were shown to reduce the risk of adults getting COVID-19 by over 90%.
Pfizer and BioNTech’s vaccine study involved over 43,000 participants globally and was 95% effective at reducing the risk of getting COVID-19, with only eight cases appearing in the vaccinated group versus 162 in the non-vaccinated group. Racially and ethnically diverse backgrounds were achieved, making up 42% of participants. The trial also had participants in the high-risk age group of 56-85 year olds, which made up 41%.
Moderna’s study involved more than 30,000 participants in the U.S. and was 94.5% effective at reducing the risk of getting COVID-19, with only five cases found in the vaccinated group versus 90 in the non-vaccinated group. Racially and ethnically diverse backgrounds were achieved, making up 37% of participants. Almost 25% of participants were over the age of 65, and just over 15% of people had high-risk medical conditions like diabetes and heart disease. 

Why does the vaccine need to be kept cold?

An important element of mRNA vaccine production is storage. Like many existing vaccines, the Pfizer/BioNTech and Moderna mRNA vaccines for COVID-19 need to be kept cold before use. However, these two vaccines require much colder storage than most existing vaccines in order to keep the mRNA molecules from degrading.

The Pfizer/BioNTech vaccine must be transported and stored at -70º Celsius while Moderna’s vaccine must be kept at -20º Celsius. Both vaccines can then be thawed shortly before administration. Overcoming shipment and storage challenges is therefore very important for mRNA vaccine use, especially in countries that do not have existing ultra-cold storage facilities.

Are there any side effects of the COVID-19 vaccine?    

Like any medical intervention, vaccines can cause side effects, which are known from studies to be caused by the vaccine. This often means that your immune system is doing its job and any mild symptoms typically last only a few days. Side effects are a type of adverse event. An adverse event is any health problem ranging from minor to serious, that happens after vaccination, whether it is caused by the vaccine or not.
During testing in clinical trials, mRNA vaccines did not cause any serious adverse events. There have been isolated incidents of rapid onset of allergic reaction, and of facial swelling in participants who had previously received botox; all cases were treatable and the participants have recovered. Sites that are administering vaccines are now required to have appropriate medical treatments immediately available for severe allergic reactions.
The Pfizer and BioNTech vaccine trials resulted in no serious safety concerns observed, with less than 4% of participants reporting fatigue or headache.

Moderna announced that less than 10% of participants who received the vaccine reported short-lived feelings of fatigue, headache, aches and muscle pain. Though unlikely, if you have any symptoms that concern you after you are vaccinated, call your doctor.

What are clinical trials?

Clinical trials are required research processes that study the way an intervention interacts with the body. Clinical trials typically take many years and are divided into different phases that answer specific questions about the treatment, primarily whether it is safe and effective. However, the EMA and the European National Competent Authorities (NCAs) have created expedited pathways and programmes to accelerate the process while still maintaining the same high standards. This is typically done for medicines and therapies for serious diseases with no other treatment options, or for public health emergencies such as interventions that fight COVID-19.

What is Conditional Marketing Authorisation?

During a declared public health emergency, treatment and vaccine developers can apply for a Conditional Marketing Authorisation (CMA) from the EMA and can benefit from a marketing authorisation application (MAA) rolling review. A CMA allows the use of unapproved medical products or unapproved uses of approved medical products to prevent serious or life-threatening diseases during a public health emergency. A CMA for a vaccine must meet certain required criteria, including that there are no adequate, approved, or available alternatives and that the benefits outweigh the risks. The EMA evaluates whether the criteria are met for each application they receive and takes into account all the scientific evidence about the vaccine.
So far, four conditional marketing authorisations have been granted by the Commission for the vaccines developed by BioNTech and PfizerModernaAstraZeneca and Janssen Pharmaceutica NV, following EMA positive assessment of their safety and efficacy. The science behind the AstraZeneca and Janssen vaccines does not fall under the umbrella of gene therapy. They use adenovirus vectors to deliver DNA into cells, instructing them to create antibodies and start the immune system’s response for COVID-19.

Benefits of a variety of approaches

It’s common to have multiple treatments or preventive medicines in development and having more than one option creates a variety of benefits. The world needs multiple companies with approved vaccines to manufacture the number of doses needed for vaccination of the worldwide population. More vaccine approvals will help to increase patient access and some vaccine approaches may work better in certain populations.

Where can I find additional information?

The European Centre for Disease Prevention and Control (ECDC), the European Medicines Agency (EMA) and the World Health Organization (WHO) offer credible resources about COVID-19 and vaccines for COVID-19.


Last updated: 27 May 2021
This content was adapted from the American Society of Gene and Cell Therapy Patient Information Program 
The American Society of Gene and Cell Therapy is the creator of the video content on this page

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