How do vaccines work?
Around the world, vaccines save millions of lives each year. Vaccines work by training and preparing the body’s natural defenses --- the immune system--- to recognise and fight off the viruses and bacteria they target. If the body is exposed to those disease-causing germs later, the body is immediately ready to destroy them, preventing illness.
Vaccines stimulate the human body’s own protective immune responses so that, if a person is infected with a pathogen (a micro-organism that can cause disease), the immune system can quickly prevent the infection from spreading within the body and causing disease. In this way, vaccines mimic natural infection but without actually causing a person to become sick.
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What do I need to know about the PFIZER-BioNTech vaccine?
How does the Pfizer-BioNTech vaccine work?
The first vaccine authorised in the United States was developed by the pharmaceutical company Pfizer and the German firm BioNTech. It consists of two shots, given three weeks apart. The Pfizer-BioNTech shots use messenger RNA technology which has been approved by the US Food and Drug Administration (FDA), as well as the independent Medicines and Healthcare Products Regulatory Agency (MHRA) in the United Kingdom, Health Canada COVID-19 Vaccines - Canada.ca, and the World Health Organization.
The Pfizer-BioNTech approach is different from that of more traditional vaccines, which often use a weakened or dead version of a virus, or a laboratory-generated protein. The Pfizer vaccine uses genetic information that is wrapped in a protective fat layer to keep it from breaking apart. When the vaccine is injected into cells in the muscle of the upper arm, it contains molecular instructions that tell your cells to create a protein that triggers an immune response to the spike protein on the surface of the coronavirus. This means your immune system will be prepared to eliminate the COVID-19 pathogen if it tries to invade your body.
Is the vaccine safe?
The Pfizer vaccine has passed rigorous safety reviews by the FDA. The FDA regulates vaccines in the United States. Vaccines must undergo a rigorous review of laboratory, clinical, and manufacturing data to ensure the safety and effectiveness of these products. Vaccines approved may also be required to undergo additional studies to further evaluate the vaccine and often to address specific questions about the vaccine's safety, effectiveness, or possible side effects.
On 11th December 2020, the FDA issued an Emergency Use Authorization (EUA) for the use of the Pfizer-BioNTech COVID-19 Vaccine. The FDA authorised the Pfizer vaccine for people age 16 and over after reviewing data from 44,000 participants in a randomised clinical trial.
What are some of the side effects of the vaccine?
A 53-page analysis by the agency found that some people who received injections had minor unpleasant but tolerable side effects, including fatigue, headaches, muscle pain, joint pain, chills and fever. Reviewers said the two months of follow-up on 38,000 of those participants provide evidence of “a favorable safety profile, with no specific safety concerns identified that would preclude issuance of an [emergency authorization].” The issuance of an Emergency Use Authorization (EUA) is different than an FDA approval (licensure) of a vaccine. It is important to emphasise that those adverse reactions are within what is to be expected from any vaccine.
In determining whether to issue an EUA for a product, the FDA evaluates the available evidence and assesses any known or potential risks and any known or potential benefits. And if the benefit-risk assessment is favorable, the product is made available during the public health emergency.
Once a manufacturer submits an EUA request for a COVID-19 vaccine, the FDA then evaluates the request and determines whether the relevant statutory criteria are met, taking into account the totality of the scientific evidence about the vaccine that is available to the agency.
The decision by the UK regulatory authority was made with advice from the Commission on Human Medicines (CHM), the government’s independent expert scientific advisory body. A dedicated team of Medicines and Healthcare Products Regulatory Agency (MHRA) scientists and clinicians carried out a rigorous, scientific and detailed review of all the available data, starting in October 2020.
This was done using a regulatory process known as a ‘rolling review’. A ‘rolling review’ can be used to complete the assessment of a promising medicine or vaccine during a public health emergency in the shortest time possible. This is done as the packages of data become available from ongoing studies on a staggered basis.
The MHRA expert scientists and clinicians reviewed data from the laboratory pre-clinical studies, clinical trials, manufacturing and quality controls, product sampling and testing of the final vaccine and also considered the conditions for its safe supply and distribution.
The National Institute for Biological Standards and Control, part of the agency, has been and will continue doing independent laboratory testing so that every batch of the vaccine meets the expected standards of safety and quality.
Will the vaccine protect me from getting the coronavirus?
The two-shot Pfizer vaccine has been shown to be 95% effective in randomised trials.
The FDA’s independent review found that of more than 20,000 people who received both vaccine doses, only eight contracted the coronavirus, and just one person fell seriously ill.
By contrast, 162 people in the placebo group contracted the coronavirus, and nine of those people developed serious illness. Additionally, if you are in the 5% of the population for which the vaccine is not effective, and do contract the virus, your symptoms will be reduced due to the better ability of your body to fight the virus.
Will I have to get both shots of the vaccine?
It is important to note that both doses are required (two shots, given three weeks apart) for the vaccine to be effective. A typical flu vaccine only requires one dose because it puts a weakened or inactivated virus into your body to trigger an immune response and produce antibodies. The Pfizer vaccine works differently by introducing mRNA into the body to create a spike protein of COVID-19. When you receive a dose for the first time, your body primes its system. The second dose gives the boost of immunity.
How were the vaccines made so quickly and safely?
Several different types of vaccines against SARS-CoV-2, the virus that causes the disease COVID-19, have been developed and gone through an extensive approval process. Some are based on traditional methods for producing vaccines and others use newer methods. The Pfizer vaccine which is using the newer method was the first one to receive the Emergency Use Authorization.
One of the more traditional ways of making a viral vaccine is to kill the virus with chemicals, such as is done with the flu vaccine, inactivated polio or hepatitis A vaccines, so that the virus can no longer multiply. Several inactivated SARS-CoV-2 vaccines are in development. Other vaccines are based on part of the bacteria or virus, typically one or more proteins, such as the vaccines for whooping cough (pertussis) and hepatitis B virus. For SARS-CoV-2 vaccines that focus on a part of the virus, this often means the spike protein on the surface of the virus.
Newer vaccine types include what are called viral vector vaccines, in which the SARSCoV-2 gene for the spike protein is inserted into another harmless virus to deliver the gene to human cells where the spike protein is produced. The spike protein then stimulates immune responses. The most common viral vectors are adenoviruses, which typically cause common cold-like symptoms in people but are further weakened for vaccines so they cannot cause any disease at all. Several adenovirus vector vaccines for SARS-CoV-2 are in advanced clinical testing (phase 3 clinical trials).
Finally, instead of using a viral vector, the gene for the spike protein can be used directly as a vaccine in the form of DNA or messenger RNA (mRNA). These are the newest SARS-CoV-2 vaccines. There are several mRNA vaccines in advanced clinical testing.
Traditionally, it has taken many years to develop a vaccine, confirm its safety and efficacy, and manufacture it in sufficient quantities for public use. This timeline was substantially shortened for SARS-CoV-2 vaccines in development. There are several ways this has been made possible.
Some clinical trials have combined phases 1 and 2 to assess safety and the immune responses.
Due to the high number of new cases of COVID-19 around the world, differences in disease risk between those who received the viral vaccine and those who received the placebo or comparison, the vaccine testing is faster because the world is experiencing a pandemic.
The United States and other governments invested in building the manufacturing capacity to produce large numbers of vaccine doses before the findings of the Phase 3 trials were available. Typically, vaccine manufacturers wait until the Phase 3 trial is completed and shows safety and efficacy before making such a large investment in manufacturing capacity. However, recognising the urgency due to the global pandemic, the manufacturing process began at financial risk to these manufacturers, but with the anticipation of having an approved and safe vaccine ready for distribution as soon as possible.
None of these factors that contribute to the accelerated development of a vaccine for SARS-CoV-2 imply that safety, scientific or ethical integrity are compromised, or that short-cuts have been made.
If you have any further questions, please visit our Vaccine FAQs.
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