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COVID-19 Vaccine FAQs: Vaccine Basics and Efficacy

| May 19, 2021

COVID-19 Vaccine FAQs: Vaccine Basics and Efficacy

Originally posted January 18, 2021; most recently updated May 19, 2021

Q: How does the COVID-19 vaccine work?

A: Preventing infection is essential to ending the current pandemic. A COVID-19 vaccine helps to generate immunity to the SARS-CoV-2 virus (the virus that causes COVID-19), decreasing the risk of infection with exposure.

Currently, three COVID-19 vaccines are available in the United States.

Two of the vaccines, the Pfizer/BioNTech and the Moderna, contain messenger RNA that encodes the spike protein that the SARS-CoV-2 virus uses to attach to human cells during infection. Both of these vaccines require two doses three or four weeks apart in order to achieve an optimal immune response. When muscle cells take up the mRNA and express the spike protein, it stimulates the immune system to make antibodies against it, making recipients less susceptible to contracting the SARS-CoV-2 virus.

A third vaccine for COVID-19 was granted Emergency Use Authorization in late February. This vaccine is made by Johnson & Johnson (J&J) and uses an adenoviral vector that cannot replicate and contains DNA for the spike protein. Then, as with the mRNA vaccines, the muscle cells produce the spike protein which stimulates the immune system to make protective antibodies. This vaccine only requires a single dose.

Q: Can someone get COVID-19 from the vaccine?

A: It is not possible to get COVID-19 from any of the available vaccines. The mRNA vaccines encode only the information for the spike protein of the virus. Similarly, the J&J uses an adenovirus vector which codes for the same spike protein as the mRNA vaccines. Vaccines undergo rigorous testing through clinical trials to ensure they are safe and effective for those who receive them. The COVID-19 vaccines are being held to the same rigorous safety and effectiveness standards as all other types of vaccines in the United States.

Most side effects, if any, are similar to other vaccines, including soreness at the injection site, muscle aches, fatigue, or mild fever.

Q: Are there any safety concerns with the new technologies (mRNA and nanotechnology) being used in the development of COVID-19 vaccines?

A: There are no known additional risks of mRNA vaccines or lipid nanoparticles. Live attenuated viral vaccines, such as measles vaccine, induce an immune response by using a virus that can replicate but not cause infection. mRNA vaccines, on the other hand, simply give the body instructions to produce one very specific part of a virus – in this case, the spike protein, which induces an immune response. Because mRNA is broken down very quickly in the human body, the mRNA is wrapped in lipid nanoparticles to protect it and allow it to enter cells. Once it gets into the cells to deliver the instructions, the mRNA breaks down very quickly. It does not get into the nucleus of the cell, is not inserted into the genome and it does not change your DNA.

Although these are the first mRNA vaccines licensed for use, researchers have been studying and working with mRNA vaccines for decades. mRNA vaccines have been studied for flu, Zika, rabies, and cytomegalovirus and no safety concerns were identified.

Q: How effective are the COVID-19 vaccines currently available in the United States? Are there advantages or disadvantages to receiving the Pfizer vs. Moderna vs. Johnson & Johnson vaccine? If patients have a choice, which vaccine should they receive?

A: This STAT article provides a good side-by-side comparison of the Pfizer, Moderna, and Johnson & Johnson vaccines. The College also has a helpful comparison of the three vaccines.

All three COVID-19 vaccines have been shown to be highly effective in phase 3 clinical trials of diverse populations of adults. In the phase 3 clinical trial data published in the New England Journal of Medicine, both of the mRNA vaccines, Pfizer and Moderna, lowered the chance of developing symptomatic COVID-19 by around 95% as compared with placebo. This is remarkably effective when compared to the flu vaccine, which is typically 40-60% effective. The phase 3 clinical trial data for the Johnson & Johnson vaccine was reportedly less effective, but this varied by site and likely reflects the variants of COVID circulating in the community. The efficacy against moderate to severe COVID-19 infection 28 days after vaccination was 72% in the United States, 66% in Latin America and 57% in South Africa. The J&J vaccine was 100% effective at preventing hospitalization and death in people in the trial who got sick with COVID-19. In addition, early evidence suggests that the J&J vaccine might also provide protection against asymptomatic infection.

An important caveat to the favorable efficacy results in the clinical trials is that the performance of the vaccines in clinical practice – the effectiveness – may be different. Although the participants in both studies included people at high risk for COVID-19 complications, participants had to be clinically stable and sufficiently healthy to come in for their study visits. There is emerging evidence that some immunosuppressed patients may not respond as well to the vaccine. Also, the effectiveness of the vaccine has shown to differ depending on the variants circulating in the community. Population-based studies that include hundreds of thousands of people ultimately will give us a better sense of these “real world” data.

Q: What percentage of the population needs to get vaccinated to achieve herd immunity to COVID-19?

A: Herd immunity is a term used to describe when enough people have protection – either from previous infection or vaccination – that it is unlikely a virus or bacteria can spread and cause disease. As a result, everyone within the community is protected even if some people don’t have any immunity themselves. The percentage of people who need to have protection in order to achieve herd immunity varies by disease. Experts estimate that at least 70% of the population would need to have immunity, either through infection or vaccination, to achieve herd immunity to COVID-19.

Q: Should patients still get a seasonal influenza vaccine annually? What is the recommended interval in relationship to receiving the COVID-19 vaccine?

A: Yes, it is very important to get the influenza vaccine, particularly since influenza can cause symptoms similar to COVID-19. Reducing the number of people who get severe influenza and require hospitalization will also help ensure that the health care system, hospitals and intensive care units will not be overwhelmed should there be an increase in COVID-19 cases during flu season. According to the CDC, COVID-19 vaccines and other vaccines may now be administered without regard to timing. This includes simultaneous administration of COVID-19 vaccines and other vaccines on the same day, as well as coadministration within 14 days.

Q: What is the College’s approach to a COVID-19 vaccine?

A: The College strongly recommends frontline workers, essential workers, and patients with high-risk medical conditions receive the COVID-19 vaccine in order to protect patients and community members they come into contact with.

The College recognizes that recommending vaccination to health care workers and patients is a vital step in creating a healthier community and finding a path back to normalcy. However, our team of experts are hard at work ensuring the vaccines are effective and the benefits outweigh any potential risks prior to administering it to members or patients.

COVID-19 Vaccine FAQs

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