COVID-19 vaccine
A COVID19 vaccine is a vaccine designed to induce immunity against SARS-CoV-2, the virus responsible for coronavirus disease 2019. COVID-19 vaccines help reduce the risk of severe illness, hospitalisation and death from the virus.
COVID‑19 vaccines were developed at an unprecedented pace to tackle the COVID-19 pandemic, with the first clinical trials beginning in March 2020. Before approval, vaccines underwent the standard three phases of clinical trials, although phases were conducted in parallel to accelerate development. Vaccines have been developed based both on classical technologies, and novel platforms.
Prior research on coronaviruses causing severe acute respiratory syndrome and Middle East respiratory syndrome accelerated the development of various vaccine platforms in early 2020. The 2023 Nobel Prize in Physiology or Medicine was awarded to Katalin Karikó and Drew Weissman for the development of effective mRNA vaccines against COVID19.
Major vaccines include the Pfizer–BioNTech mRNA vaccine, Moderna mRNA vaccine, and the Novavax protein subunit vaccine. With the emergence of new SARS-CoV-2 variants, the original vaccines—particularly Pfizer–BioNTech and Moderna vaccines—have been updated. These "variant-adapted" vaccines are offered as booster doses. The immunity from the vaccines also wanes over time, requiring people to get boosters to maintain protection.
Common side effects of COVID19 vaccines include soreness, fatigue, headache, myalgia, and arthralgia, which resolve without medical treatment within a few days. COVID19 vaccination is safe for people who are pregnant or are breastfeeding.
The COVID19 vaccines are widely credited for their role in reducing the spread of COVID19 and reducing the severity and death caused by COVID19. Many countries implemented phased distribution plans that prioritized those at highest risk of complications, such as the elderly, and those at high risk of exposure, such as healthcare workers. By December 2020, more than 10 billion vaccine doses had been preordered, with about half of the doses purchased by high-income countries comprising 14% of the world's population., over 13billion doses of COVID19 vaccines have been administered worldwide.
Background
Before COVID19, a vaccine for an infectious disease had never been produced in less than several yearsand no vaccine existed for preventing a coronavirus infection in humans. However, vaccines have been produced against several animal diseases caused by coronaviruses, including infectious bronchitis virus in birds, canine coronavirus, and feline coronavirus.Previous projects to develop vaccines for viruses in the family Coronaviridae that affect humans have been aimed at severe acute respiratory syndrome and Middle East respiratory syndrome. Vaccines against SARS and MERS have been tested in non-human animals.
According to studies published in 2005 and 2006, the identification and development of novel vaccines and medicines to treat SARS were priorities for governments and public health agencies worldwide at the time. There is no cure or vaccine proven to be safe and effective against SARS in humans. There is also no proven vaccine against MERS. When MERS became prevalent, it was believed that previous SARS research might provide a useful template for developing MERS vaccines. As of March 2020, there was one MERS vaccine that completed PhaseI clinical trials in humans, and three others in progress, all being viral-vectored vaccines: two based on adenoviruses and one on MVA.
Vaccines that use an inactive or weakened virus that has been grown in eggs typically take more than a decade to develop. In contrast, mRNA is a molecule that can be made quickly, and research on mRNA to fight diseases was begun decades before the COVID19 pandemic by scientists such as Drew Weissman and Katalin Karikó, who tested on mice. Moderna began human testing of an mRNA vaccine in 2015. Viral vector vaccines were also developed for the COVID19 pandemic after the technology was previously cleared for Ebola.
Vaccine technologies
The initial focus of SARS-CoV-2 vaccines was on preventing symptomatic, often severe, illness. Most of the first COVID19 vaccines were two-dose vaccines. Exceptions were the single-dose vaccines Convidecia and the Janssen COVID‑19 vaccine, and vaccines with three-dose schedules, Razi Cov Pars and Soberana.In July 2021, at least nine different technology platforms were under research and development to create an effective vaccine against COVID19. The coronavirus spike protein, with the virus uses to enter the cell, induces a strong immune response and is therefore the primary target of vaccines.
However, other coronavirus proteins were also being investigated for vaccine development, for example, the nucleocapsid proteins, because they also induce a robust T-cell response, while their genes are more conserved and recombine less frequently. Future generations of COVID19 vaccines targeting more conserved genomic regions could be used to treat future variations of SARS-CoV-2, or any similar coronavirus epidemic/pandemic.
Platforms developed in 2020 involved nucleic acid technologies, non-replicating viral vectors, peptides, recombinant proteins, live attenuated viruses, and inactivated viruses.
Many vaccine technologies developed for COVID19 use "next-generation" strategies for precise targeting of COVID19 infection mechanisms. Several of the synthetic vaccines use a 2P mutation to lock the spike protein into its prefusion configuration, stimulating an adaptive immune response to the virus before it attaches to a human cell.
mRNA vaccines
Several COVID19 vaccines, such as the Pfizer–BioNTech and Moderna vaccines, use RNA to stimulate an immune response. When introduced into human tissue, the vaccine contains messenger RNA, which causes cells to express the SARS-CoV-2 spike protein. This teaches the immune system to identify and destroy the corresponding pathogen. RNA vaccines often use nucleoside-modified messenger RNA. The delivery of mRNA is achieved by encapsulating the molecule in lipid nanoparticles, which protect the RNA strands and help their uptake into the cells.mRNA vaccines were the first COVID19 vaccines authorised in the United Kingdom, the United States, and the European Union. Authorized vaccines of this type include the Pfizer–BioNTech
Severe allergic reactions to the mRNA vaccines are rare. In December 2020, 1,893,360 first doses of Pfizer–BioNTech COVID19 vaccine administration resulted in 175 cases of severe allergic reactions, of which 21 were anaphylaxis. For 4,041,396 Moderna COVID19 vaccine dose administrations in December 2020 and January 2021, only ten cases of anaphylaxis were reported. Lipid nanoparticles were most likely responsible for the allergic reactions.
In May 2025, a different version of the Moderna COVID-19 vaccine, with the trade name Mnexspike, was approved for medical use in the United States.
In June 2025, the European Medicines Agency announced that it was making data from the marketing authorization applications for COVID19 mRNA vaccines Comirnaty and Spikevax publicly available.
Viral vector vaccines
Viral vector vaccines use a modified version of a virus to generate immunity. For COVID-19, these vaccines were based of a modified adenovirus, which normally causes the common cold. It is first made harmless, by removing the genes that cause illness and those responsible for replication. The virus is further modified so that it contains DNA that encodes a SARS‑CoV‑2 protein. As such, the virus in the vaccine does not make new adenovirus copies, but only produces the antigen that elicits a systemic immune response.Unlike mRNA vaccines, which usually require freezer storage, DNA vaccines such as adenovirus vector vaccines can be kept in a fridge.
Authorized vaccines of this type include the Oxford–AstraZeneca COVID‑19 vaccine,
Sputnik V uses Ad26 for its first dose, which is the same as Janssen's only dose, and Ad5 for the second dose, which is the same as Convidecia's only dose. In August 2021, the developers of Sputnik V proposed, in view of the Delta case surge, that Pfizer test the Ad26 component as a booster shot.
Inactivated virus vaccines
s consist of virus particles grown in culture and then inactivated by methods such as heat or formaldehyde, thereby losing their disease-producing capacity while still stimulating an immune response.Inactivated virus COVID-19 vaccines are less efficient than mRNA vaccines, because the process of de-activating the virus causes the spike protein to change slightly, whereas mRNA vaccines show the spike protein in its normal state. This makes parts of the protein inaccessible to the immune system. The immunity does not last as long as with mRNA vaccines, so that additional boosters are required to maintain immunity.
Inactivated virus vaccines authorized in China include the Chinese CoronaVac and the Sinopharm BIBP
Subunit vaccines
s present one or more antigens without introducing whole pathogen particles. The antigens involved are often protein subunits, but they can be any pathogen-derived molecule or its fragment.The authorized vaccines of this type include the peptide vaccine ZF2001, MVC-COV1901, Corbevax, the Sanofi–GSK vaccine, and Soberana 02. Bimervax was approved for use as a booster vaccine in the European Union in March 2023. The Novavax COVID‑19 vaccine is another subunit vaccine. This vaccine is produced by infecting moth cells with a modified baculovirus vector, which contains a gene for a SARS-CoV-2 spike protein.
The clinical trials of V451 vaccine were terminated after it was found that the vaccine may potentially cause incorrect results for subsequent HIV testing.
Virus-like particle vaccines are one type of subunit vaccines. They look similar to viruses, but do not contain any RNA or DNA, and are non-replicating. They can be stored in a fridge, rather than using extreme cold like mRNA vaccines. One such vaccine, Covifenz, was authorized for use in 2022 in Canada, but later withdrawn.