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COVID-19 Vaccines

Published on Dec 22, 2020 and last reviewed on Apr 26, 2021   -  14 min read


A COVID-19 vaccine provides acquired immunity against the new Coronavirus. Read the article to know everything about the approved and undertrial vaccines.

COVID-19 Vaccines

Many pharmaceutical companies worldwide are working on potential vaccines for the new Coronavirus disease (COVID-19). With COVID-19 cases continuing to grow, scientists and doctors are working day and night to develop vaccines to slow the pandemic and lessen its damage.

How COVID-19 Vaccines Work?

Generally, when a virus or pathogen enters our bodies, they attack the cells and multiply. The body's immune system prevents this infection from progressing with the help of different types of white blood cells. Macrophages (one type of white blood cells) engulf and digest the virus and damaged cells. These macrophages leave behind some parts of the virus called antigens. B-lymphocytes, defensive white blood cells, produce antibodies that try to destroy the antigens left behind by macrophages. T-lymphocytes, another type of white blood cells, attack the infected cells in the body.

All these processes take a few days to weeks, and the immune system eventually fights the infection off (ideally). After the initial infection, the immune system remembers how to fight off that particular pathogen if it invades the body again. Some T-lymphocytes or memory cells remain in the body, and they attack immediately if the body reencounters the same virus.

COVID-19 vaccines are designed to provide the same immunity without getting infected with the virus. Different types of vaccines work in different ways, but in the end, all the vaccines lead to the formation of B and T-lymphocytes. These cells remember how to fight that virus in case the person gets infected in the future. The case division between vaccinated individuals and those who took the placebo indicates a vaccine efficacy rate above 90%, seven days after the second dose. This means that protection is obtained 28 days after the vaccination initiation, which consists of a 2-dose schedule.

What Are the Types of COVID-19 Vaccines?

The four main types of COVID-19 vaccines are:

  1. Whole Virus Vaccines - Many vaccines use the entire virus, either in the live-attenuated form or inactivated form, to trigger an immune response. Live-attenuated vaccines use a weakened form of the virus, which cannot cause illness but can replicate. While viruses with a destroyed genetic material can no longer multiply, they can activate the immune system and are used in inactivated vaccines.

  2. Protein Subunit Vaccines - They contain viral protein, which triggers the immune system to make T-lymphocytes and antibodies. Only using the protein minimizes the risk of side effects, but the immune response might also be weak, which is why they often require adjuvants to boost the immune response.

  3. Nucleic Acid Vaccines - These vaccines either use viral spike protein or the viral RNA or DNA. When this genetic material enters the human cells, it uses our cells to make the viral antigen, which triggers an immune response. These vaccines are easier to make and are cheaper.

  4. Viral Vector Vaccines - These vaccines also give our cells instructions to produce viral antigens. But instead of using the nucleic acid from the virus, it uses a harmless virus (not the one against which the virus is targeted). Adenovirus (the virus that causes the common cold) is often used as a vector. The side effect of this vaccine is as many might already be exposed to various adenoviruses, and when it is used as a vector, the immunity destroys it, which results in an inadequate immune response.

COVID-19 Vaccine Timeline:

A COVID‑19 vaccine is intended to provide immunity or protection against the new Coronavirus (SARS-CoV-2). Before the current pandemic, as scientists were working on developing vaccines against SARS - Severe acute respiratory syndrome and MERS - Middle East respiratory syndrome, which are diseases caused by other strains of Coronaviruses, they already had an idea about the structure and function of this virus. This has accelerated the work that is being done for COVID‑19 vaccines. The work began on these vaccines in January, soon after the virus's genome was deciphered.

In November 2020, Moderna, BioNTech and Pfizer Inc, Gamaleya Institute, and the University of Oxford announced positive vaccine trial results. By December 2020, almost 40 vaccines were in Phase I to II of their clinical trials and 17 in Phase II to III. And by 19th December 2020, 16 countries had approved the BioNTech and Pfizer Inc vaccine (Tozinameran) for emergency use. United Aram Emirates (UAE) and Bahrain have authorized the vaccine manufactured by Sinopharm (China National Pharmaceutical Group Corp). By 16th December in the UK, around 1,38,000 people have received Tozinameran. The FDA (the United States Food and Drug Administration) granted an Emergency Use Authorization (EUA) for Tozinameran On 11th December 2020 and also granted a EUA for the Moderna vaccine (mRNA-1273) a week later.

Approved COVID-19 Vaccines:

1) Pfizer, BioNTech, and Fosun Pharma - The pharmaceutical company Pfizer, in collaboration with BioNTech (a German biotech company) and Fosun Pharma, developed a two-dose mRNA vaccine (Tozinameran or BNT162b2). After conducting trials on children and adults on 9th November, the company's data showed that the vaccine was 90 % effective. The FDA then reported that the Pfizer vaccine, after the first dose, gave some protection and almost full protection after the second dose on 8th December, and on 11th December, this vaccine was given the EUA by the FDA. Reports showed an allergic reaction in a healthcare worker. The usage of this vaccine was recommended in people who are over 16 years of age. The sites that got approved to administer vaccinations in Alaska declared that they must have medications on hand to deal with an allergic response. They began testing this vaccine in children under 12 years to expand the age range by early 2022. The first shots were administered to volunteers on 24th March 2021.

2) Moderna (National Institutes of Health) - It is a two-dose mRNA vaccine (mRNA-1273) that began testing in March. In August, the company's data showed a favorable immune response in 10 people between the ages of 56 and 70 and over the age of 70. In November, reports indicated the vaccine to be 94 % effective. And in mid-December, this vaccine was given EUA by the FDA. This vaccination is given in 2 doses at a time interval of 28 days. In clinical trials, common side effects were noted. They were only mild. These kinds of effects were noted in the first seven days after vaccination.The vaccines do not contain any live coronavirus, so it is impossible to develop COVID-19 due to a vaccination.

3) Gamaleya Research Institute - It is a Russian institute, which developed a vaccine (Sputnik V or Gam-COVID-Vac) that has two components, a recombinant adenovirus type (rAd26) and type 5 (rAd5) vectors. In August, the vaccine received a "conditional registration certificate." The ongoing clinical trial in Russia involves 40,000 volunteers, and clinical trials have been announced in the UAE, India, Venezuela, and Belarus. The results of phase I and II trials found that the vaccine showed an immune response with mild side effects. The Sputnik V vaccine is 91.4 % efficient with mild side effects, and its vaccine efficacy against severe cases of Coronavirus is 100 %. After ensuring all the safety standards, Data and Safety Monitoring Board (DSMB) recommended a shift to phase III from phase II. Phase III approval for conducting trials in India was approved recently. Sputnik V depends on the virus’s genetic instructions for developing the spike protein. Sputnik V uses double-stranded DNA, unlike the Pfizer-BioNTech and Moderna vaccines, which build the instructions in a single-stranded RNA.

4) Sinovac Biotech - This is a Chinese company that developed an inactivated SARS-CoV-2 vaccine (CoronaVac). The phase III trials began in Brazil, Indonesia, and Turkey. The vaccine was granted emergency approval by the Chinese government for use on individuals at high risk of developing severe COVID-19 infection.Initial researchers in Brazil found that this vaccine was 78% effective. Later, the percentage was adjusted to 50.4%. Sinovac has provided 160 million vaccine doses to 18 countries and territories, including China, with over 70 million doses administered. Sinopharm published on 30 December that stage three trials of the vaccine revealed that it was 79% effective - more inferior than that of Pfizer and Moderna. However, the United Arab Emirates, which supported the Sinopharm vaccine earlier this month, said that the vaccine was 86% effective, according to interim results of its stage three trial. Sinovac said that the COVID-19 vaccine is safe in children between the ages of 3 to 17. Once administered, two recipients acquired high fevers in response to the vaccine, one a 3-year-old and a 6-year-old. The rest of the trial subjects felt only mild symptoms.

5)Wuhan Institute of Biological Products and Sinopharm- The vaccine BBIBP-CorV, an inactivated virus vaccine, is being tested by the Chinese company Sinopharm and developed by the Wuhan Institute of Biological Products. As the phase I clinical trial showed positive results, phase III trials began first in UAE and then in Morocco and Peru, which showed an efficacy of 86%. Bahrain and UAE have already approved the vaccine for use.

6) Bharat Biotech, Indian Council of Medical Research, and Indian National Institute of Virology - The inactivated virus vaccine (BBV152 or Covaxin) developed by the Indian company Bharat Biotech in collaboration with the Indian National Institute of Virology began the phase III trial in October. The report on Phase I trials showed the vaccine to be safe and produce antibodies against SARS-CoV-2. More than 26,000 participants were involved in phase III trials and now Covaxin has been declared as the first official vaccine in India. This whole virion inactivated COVID-19 vaccine candidate confirmed a temporary vaccine efficiency of 81% in its Phase 3 clinical trial. The trials comprised 25,800 subjects, the largest ever conducted in India, in conjunction with the Indian Council of Medical Research.

7. AstraZeneca and the University of Oxford (Covishield in India) - In April 2020, AstraZeneca and the University of Oxford announced the development of a recombinant adenovirus vaccine (AZD1222), which was based on a chimpanzee adenovirus that carries coronavirus proteins in the body. Phase III clinical trials began in Brazil, the US, and South Africa in August. When a volunteer developed transverse myelitis (a spinal inflammatory disorder), the study was halted in September 2020. A week later, the trials restarted in the UK and Brazil, and the FDA authorized the US trial to resume in October 2020. It was reported in November 2020 that the vaccine produced a strong immune response in a clinical trial involving participants over 70 years of age. But, the data released on 8th December 2020 showed that the vaccine was only 70 % effective. The efficiency was identified to be around 62% when they were administered in two separate and full doses. An increase in the efficiency up to 90% was achieved when the vaccine was given as a half dose followed by a full dose. Leaving a more extended gap between the first and second doses enhances the jab's overall effectiveness - in a sub-group given the vaccine this way, it was observed to be 70% effective after the first dose.

But recently, blood clots and unusual bleeding in a small number of vaccine recipients in European countries have cast doubt on its safety. However, no causative link has been observed between the patients' conditions and the vaccine. The reports have prompted more than a dozen countries to either partly or wholly suspend the vaccine's use while the cases are investigated. Most of the nations said they were doing so as a precaution until leading health agencies could review the cases. However, most countries continued using it after the European Medicines Agency conducted research and declared on 18th March 2021 that the AstraZeneca vaccine is safe and efficient. The EMA said the vaccine's benefits far outweighed the potential risks and pointed out that post-vaccine blood clots' rate was lower than the expected rate in the general population. After several days of uncertainty around the AstraZeneca COVID-19 vaccine trial results in the United States, the company confirmed efficacies of 76% against symptomatic disease and 100% against severe illness and hospitalization.

8. Johnson & Johnson - In late July 2020, Johnson & Johnson began a phase I/II trial in humans after their adenovirus vaccine (Ad26.COV2.S) showed positive results in monkeys. In September 2020, a phase III trial with 60,000 participants began to test their one-dose vaccine. Due to unexplained illness in one of the participants, the trial was paused in October 2020. The study will resume in the US, and the company said that the vaccine would be ready for FDA approval by February 2021. The results for the clinical trials from phase III have not arrived and so it is difficult to predict the efficiency of this vaccine. The company still said it found no proof that the vaccine had caused the disease and declared on 23 October 2020 that it would continue the trial. On 29 January 2021, Janssen proclaimed safety and efficacy data from an interim investigation of ENSEMBLE trial data. The vaccine was 66% effective at restricting the combined endpoints of moderate and severe COVID-19 at 28 days post-vaccination amongst all volunteers. A second Phase III clinical test called ENSEMBLE 2 began recording on 12 November 2020. ENSEMBLE 2 differs from ENSEMBLE in that it will analyze participants will get two intramuscular (IM) shots of Ad26.COV2.S, on day 1 and the next on the 57th day.

In February 2021, the U.S. Food and Drug Administration announced an emergency use authorization (EUA) for the third vaccine for the restriction of coronavirus disease 2019 (COVID-19) induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The EUA supports the Janssen COVID-19 Vaccine to be administered (single-shot) in the U.S. for use in people who are above 18 years of age. Thailand also cleared Johnson & Johnson’s single-shot COVID-19 vaccine for local emergency use, the third manufacturer to win the approval.

Ongoing COVID-19 Vaccine Projects:

1) Inovio - This pharmaceutical company designed the vaccine INO-4800, a nucleic-acid-based vaccine, in January 2020. Following authorization by the FDA, they started the human clinical trial in April 2020. After they got clearance from the FDA in November 2020, Phase II of the trial is ongoing. Inovio's DNA medicines release optimized plasmids instantly into cells intradermally or intramuscularly, employing Inovio's proprietary hand-held smart device called Cellectra. The Cellectra device uses a short electrical pulse to reversibly penetrate tiny pores in the cell to allow the plasmids to enter, succeeding a fundamental limitation of other DNA and other nucleic acid strategies, such as mRNA. Once inside the cell, the DNA plasmids allow the cell to generate the targeted antigen. The antigen is prepared naturally in the cell and triggers the desired T cell and antibody-mediated immune responses. Administration with the Cellectra device guarantees that the DNA medicine is efficiently transferred directly into the body's cells, where it can work to stimulate an immune response.

2) Sanofi and GlaxoSmithKline (GSK) - These French and Britain pharmaceutical companies developed an adjuvanted protein vaccine. Initial results from a phase I/II clinical trial in December 2020 showed a poor immune response in older adults but sufficient immune response in adults between 18 and 49. The company is believed to launch the next phase of the trial in February 2021. A delay in the development of this vaccine is noted in order to enhance the results in older people. The Sanofi/GSK vaccine is a recombinant protein-based vaccine depending on the baculovirus commonly seen in moths. Pieces of the novel coronavirus are applied in sequence with the baculovirus to efficiently program the immune system to recognize better and fight COVID-19. There are several other recombinant vaccines in the developing stage from other pharmaceutical companies.

3) Sanofi and Translate Bio - The French drugmaker Sanofi is also working with Translate Bio, and they developed an mRNA vaccine in February 2020. Nonhuman trials conducted on monkeys and mice showed a strong immune response. The phase II trial results will be available soon, and the phase III study will start in early 2021. The vaccine is expected to be approved in the second half of 2021.

4) CanSino Biologics - China's CanSino Biologics Inc., backed by the Chinese military, is also developing a potential COVID-19 vaccine. They are using an adenovirus Ad5 to carry coronavirus proteins into the cells. The protein elicits an immune response when combined with another compound, called the adjuvant. This vaccine is called Ad5-nCoV or Convidecia. In July 2020, it was reported that the participants in the phase II trial showed a strong immune response to the vaccine. As older adults had a weaker response, two doses might be needed for them. The Chinese military approved the vaccine in June, and it was administered to the armed forces. As of December 2020, over 20,000 participants have enrolled for late-stage human trials in Pakistan, Saudi Arabia, and Russia.

6) Novavax - The SARS-CoV-2 recombinant spike protein nanoparticle with an adjuvant vaccine (NVX-CoV2373) developed by Novavax received massive funding from the Coalition for Epidemic Preparedness Innovations (CEPI). The virus proteins are attached to microscopic particles to form this vaccine. In August 2020, a phase II trial was launched in South Africa, and a phase III trial began in the UK a month later. In September 2020, a COVID-19 vaccine manufacturing agreement was made with the Serum Institute of India to produce over 2 billion doses annually. Now, Novavax is eliminated from the emergent facility because of the lack of personal manufacturing units.

7) University of Queensland and CSL - The university, along with CSL, developed the UQ-CSL v451 COVID-19 vaccine. Phase I trial of this vaccine showed a robust response towards the virus. The vaccine was developed by growing viral proteins in cell cultures. No serious side effects or safety concerns were reported in the 216 participants. Still, as participants returned false-positive test results for HIV, it was decided that the vaccine will not go into phase II/III clinical trials.

8) Beijing Institute of Biological Products and Sinopharm - Sinopharm is also testing another inactivated virus vaccine developed by the Beijing Institute of Biological Products. In June 2020, phase III trials began in the UAE and Argentina (in September). In September 2020, this vaccine was approved by UAE to use on healthcare workers. The analysis report from the three clinical trials proved the efficiency to be about 86%.

9) Medicago and GlaxoSmithKline (GSK) - GSK and Medicago developed a COVID-19 candidate vaccine combining recombinant Coronavirus Virus-Like Particles (CoVLP) with an adjuvant system. CoVLP mimics the structure of the SARS-CoV-2 virus, resulting in an immune response. Pre-clinical results using this single-dose vaccine demonstrated high levels of neutralizing antibodies. Medicago, a biopharmaceutical company and GlaxoSmithKline (GSK), started Phase III clinical research of Medicago's plant-derived COVID-19 vaccine candidate in sequence with GSK's pandemic adjuvant, as part of the ongoing Phase II/III study.

10) CureVac and Coalition for Epidemic Preparedness Innovations (CEPI) - This company has developed an mRNA vaccine (Zorecimeran or CVnCoV), which showed antibody responses comparable to the one found in recovered COVID-19 patients. Phase IIb and III trials were initiated in December 2020. Nearly 35,000 participants were included in this trial. An interim analysis is planned to be carried out in the first quarter period of 2021. CVnCoV is an mRNA vaccine that encodes a minimum piece of the coronavirus spike protein and stimulates the immune system against it. CVnCoV technology does not associate with the human genome under typical conditions, that is, in the absence of example, an active retrovirus infection.

12. Needle-Free COVID-19 Vaccines or Inhaled Vaccine:

The company had not yet published news about the inhaled version of the vaccine. According to the company, previous trials involving the injectable product had shown 95.47% efficacy in preventing severe COVID-19 disease two weeks post-vaccination. The currently-approved COVID-19 vaccines on the market are delivered as intramuscular injections in the deltoid muscle. However, some researchers have already studied different vaccine administration techniques. The National Medical Products Administration approved the inhaled vaccine trial. Experts have assumed that the next generation of COVID-19 vaccine may comprise needle-free options, potentially eliminating hesitancy among groups with sensitivity to needles.

Oxford University said on Thursday that it was beginning a study to test the immune responses of a nasal administration of its COVID-19 vaccine generated with AstraZeneca, with 30 healthy volunteers aged 18 to 40 for the initial experiment. British researchers last September said that they would test inhaled versions of COVID-19 vaccine candidates produced by Oxford University and Imperial College to see whether they present any localized immune response in the respiratory tract.

The nasal spray vaccine is produced based on a regular poultry virus called the Newcastle Disease Virus (NDV), which can replicate in humans but do not harm. The research team directed NDV to create the spike proteins of the SARS-CoV-2 virus to prime the body's immune system to combat the coronavirus. The findings were announced recently on BioRxiv, a preprint server for analysis that has not yet been peer-reviewed.

Two other companies are also trying to generate a vaccine - Zydus Cadila replicating viral vectors and creating a DNA plasmid vaccine, and Hyderabad-based Bharat Biotech, in collaboration with the US-based FluGen, which is awaiting the first clinical trials of a nasal vaccine by late 2020.

13. Oral COVID-19 Vaccine:

In February 2020, immediately after the commencement of the COVID-19 pandemic, another Israeli team started developing what they considered will be an oral coronavirus vaccine. Experts from the Galilee Research Institute's biotechnology group announced that they were primed to build their vaccine within a few months.

There are various other vaccines, such as INO-4800, EpiVacCorona, Lunar-COV19/ARCT-021, LV-SMENP-DC, etc., are expected to release the phase I report shortly. About 50 vaccines are in early development over the biopharma landscape. Researchers are investigating ten different vaccine approaches, said Jim Mayne, vice president of science and regulatory advocacy at PhRMA.

Repurposed Vaccines against SARS-CoV-2:

Using an already approved vaccine (for some other infection) for protection against the new Coronavirus is called a repurposed vaccine. An Australian Institute (the Murdoch Children's Research Institute) is conducting a phase III trial using the bacillus Calmette-Guérin (BCG) tuberculosis vaccine to see its capacity to prevent COVID-19 in Australia, the Netherlands, Brazil, Spain, and the UK.

It is also believed that the polio vaccine might help the immune system to fight SARS-CoV-2, and the measles, mumps, rubella (MMR) vaccine to protect against inflammation and sepsis due to COVID-19. Nothing is proved yet.

Frequently Asked Questions


Are Moderna and Pfizer's COVID-19 Vaccines Given in Two Doses?

Yes, both Moderna and Pfizer's vaccines are given in two doses. The time between two doses is 21 days for Pfizer's vaccine and 28 days for Moderna.


How Effective Is the Pfizer COVID-19 Vaccine?

The Pfizer vaccine is 95 % effective at preventing symptomatic COVID-19 cases, according to the FDA.


How Effective Is the Moderna COVID-19 Vaccine?

According to the FDA, the Moderna vaccine is 94.1 % effective at preventing symptomatic COVID-19 cases.


Can Patients Currently Infected With COVID-19 Get Vaccinated?

Infected patients carry the risk of spreading the virus during vaccination. To avoid this, vaccinations should be scheduled 14 days after the resolution of symptoms.


Should Previously COVID-19 Infected People Get Vaccinated?

Yes, people who have already recovered from COVID-19 can get vaccinated. Such people already might have some level of immunity against the virus, but doctors are still advising them to get vaccinated when the vaccine becomes available to them.


Why Should People Who Have Had COVID-19 Still Be Vaccinated?

A few COVID-19-recovered patients do not seem to have a good immune response, and some reinfection cases have been reported, which is why getting vaccinated even if you were infected previously is the best thing to prevent COVID-19.


Should You Continue to Wear a Mask After COVID-19 Vaccine?

Getting the COVID-19 vaccine will prevent symptomatic COVID-19 infection, but scientists do not know if it can prevent you from spreading the virus to others. Until we know for sure, keep wearing your mask when you go to crowded places to protect others who might not have been vaccinated yet.


Can You Spread the New Coronavirus if You Get Vaccinated?

Even after getting vaccinated, you could still possibly carry and spread the new Coronavirus to others. So wear masks, maintain social distancing, and practice frequent hand-washing to protect others until the majority of the population gets vaccinated.


Can a Pregnant or Breastfeeding Woman Get the COVID-19 Vaccine?

There is no data available to determine if the COVID-19 vaccine poses a risk to pregnant and breastfeeding women. In the United Kingdom, pregnant and breastfeeding women are excluded from vaccination programs, and in the US, only women who volunteer will be given the vaccine. A study found that COVID-19 vaccines from Moderna and Pfizer are active in pregnant women, boosting their immune response and even transferring protective antibodies to their babies. In this study, eighty-four women were pregnant, and 31 were lactating. According to the researchers from centers including Harvard, MIT, Brigham, and Women's Hospital, pregnant and lactating women had a strong immune response to the vaccines compared to the 16 women who were not pregnant or lactating. On examining the umbilical cord blood and the placenta, they found that the babies born to women who had obtained the vaccine had "strikingly higher" levels of COVID-fighting antibodies than babies born to women who had previously had COVID-19.


What Are the Common Side Effects of COVID-19 Vaccine?

The common side effects noted so far during various drug trials are pain and swelling at the site of infection, fever, chills, headaches, and tiredness.


How Soon After Taking the COVID-19 Vaccine Are You Immune?

It can take a few weeks for the body to build immunity after getting vaccinated. So, it is possible to get infected with the new virus just before or after vaccination.


Who Will Get Vaccinated First?

With a limited supply of vaccine and scientists still trying to figure out how to safely transport big batches of vaccine, the available vaccine will be given to older adults, younger adults with comorbidities, and healthcare workers first.


Will COVID-19 Vaccine Provide Prolonged Protection?

It is too early to comment on the long-term protection of COVID-19 vaccines. While initial data from the clinical trials are encouraging, we just have to wait and watch.


Is It Compulsory to Get the COVID-19 Vaccine?

You can choose not to get vaccinated, and it is totally voluntary. But, it is advisable to receive all the doses of the COVID-19 vaccine for protection against the infection and to prevent the spread to others.

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Last reviewed at:
26 Apr 2021  -  14 min read




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