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COVID-19 Vaccine FAQs: Vaccine Basics and Efficacy

| August 20, 2021

COVID-19 Vaccine FAQs: Vaccine Basics and Efficacy

Originally posted January 18, 2021; most recently updated September 24, 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 February, 2021. 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: What are the safety concerns with the COVID-19 vaccines? Does the mRNA technology pose additional safety concerns over traditional vaccines?

A: The CDC reports that over 386 million doses of COVID-19 vaccines have been given in the United States from December 14, 2020 through September 22, 2021. The vaccines have undergone and will continue to undergo the most intensive safety monitoring in U.S. history. The safety monitoring has identified several, yet very rare, types of health problems after vaccination including:

  1. Anaphylaxis (after mRNA vaccines)
    Anaphylaxis to the mRNA COVID-19 vaccines is currently estimated to occur approximately 5 cases per 1 million doses, compared to 1.3 per 1 million doses, which is the incidence of anaphylaxis associated with other vaccines.The anaphylaxis rate for the J&J COVID-19 vaccine has not been reported but is likely to be closer to the general incidence seen with other vaccines.The CDC has provided recommendations for COVID 19 vaccine providers about how to prepare for the possibility of a severe allergic reaction. All people who get a COVID 19 vaccine are required to be monitored on site. People who have a history of severe allergic reactions to vaccines or other injectable therapy are monitored for at least 30 minutes after getting the vaccine. All other people are monitored for at least 15 minutes after getting the vaccine.
  2. Thrombosis with Thrombocytopenia Syndrome – a syndrome of blood clots occurring with low platelets (after J&J).TTS has occurred after receiving the J&J/Janssen COVID 19 vaccine and not after the mRNA vaccines at a rate of about 7 per 1 million vaccinated women between 18 and 49 years old. For women 50 years or older and men of all ages, this adverse event is even more rare.
  3. Myocarditis and Pericarditis (mRNA vaccines)
    The FDA issued a warning in June about heart inflammation. Since April 2021, there have been more than one thousand reports to the Vaccine Adverse Reporting System (VAERS) of myocarditis and pericarditis occurring in adolescents and young adults more often after getting the second dose than after the first dose of one of the two mRNA vaccines. Symptoms typically occur within several days after vaccination and patients have been able to return to their normal daily activities after their symptoms improve. Because the known and potential benefits of COVID 19 vaccination outweigh the known and potential risk, including the possible risk for myocarditis or pericarditis, the CDC continues to recommend COVID-19 vaccination for everyone 12 years of age and older.
  4. Guillain Barre Syndrome
    There’s a possible, but rare risk in developing Guillain-Barre syndrome after the Johnson and Johnson vaccine. To date, no cases of GBS have been seen in people vaccinated for COVID-19 with the mRNA vaccines.

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 a person’s 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: The College has a helpful comparison of the three vaccines.

Vaccine Developer Pfizer Moderna Johnson & Johnson/Janssen
Mechanism Messenger RNA Messenger RNA Inactivated adenovirus
Approval date December 11, 2020 December 18, 2020 February 27, 2021
% of people protected from getting infected in clinical studies 95% 94.1% 66.1% globally; 72% in the U.S.; 86% effective against severe disease
Who is it approved for? 12 years and older 18 years and older 18 years and older
How many doses are needed? 2 doses, 3 weeks apart 2 doses, 4 weeks apart One dose
When is full vaccination status achieved? 2 weeks after the 2nd dose 2 weeks after the 2nd dose 2 weeks after the dose
Boosters for Immunocompromised 3rd dose, at least 28 days after second dose 3rd dose, at least 28 days after second dose Not approved
Boosters for Others See CDC Statement on Pfizer Booster Shot Not approved Not approved
Are there any warnings? The FDA issued a warning in June, 2021 about heart inflammation. Since April, 2021, there have been more than a thousand reports of myocarditis and pericarditis. The FDA issued a warning in June, 2021 about heart inflammation. Since April, 2021, there have been more than a thousand reports of myocarditis and pericarditis. In July 2021, the FDA issued a warning about an increased risk for developing Guillain-Barre syndrome.
Contraindications to getting a COVID-19 vaccination People with a history of serious allergic reactions, anyone with a history of reactions to vaccine ingredients, including polyethylene glycol, and anyone with a history of allergic reactions to polysorbate. People with a history of serious allergic reactions, anyone with a history of reactions to vaccine ingredients, including polyethylene glycol, and anyone with a history of allergic reactions to polysorbate. Anyone who has had an allergic reaction to an ingredient in the vaccine, like polysorbate.
Vaccine performance against emerging variants – Alpha, Beta, Gamma, and Delta Highly effective against hospitalization and death for a variety of strains. Data suggest lower effectiveness against confirmed infection and symptomatic disease caused by the Beta, Gamma and Delta strains compared with the ancestral and Alpha variant. Highly effective against hospitalization and death for a variety of strains. Data suggest lower effectiveness against confirmed infection and symptomatic disease caused by the Beta, Gamma and Delta strains compared with the ancestral and Alpha variant. Effectiveness against variants currently being studied. An August 2021 study of South African health care workers showed 71% efficacy against hospitalization and 96% efficacy in preventing death from COVID-19.
Acquisition and transmission data for fully vaccinated people Current evidence indicates that fully vaccinated people are less likely than unvaccinated people to acquire SARS-CoV-2 or transmit it to others. Current evidence indicates that fully vaccinated people are less likely than unvaccinated people to acquire SARS-CoV-2 or transmit it to others. Currently being studied.

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.

Shared decision making is the best option to use when guiding patients regarding which vaccine to receive if a choice is available.

Q: What is the real-world effectiveness for the COVID-19 vaccines?

Many types of assessments to determine COVID 19 vaccine effectiveness in real-world conditions are ongoing. The CDC refers to these as vaccine effectiveness (VE) studies. Current ongoing VE studies include people with underlying medical conditions, include people who have been given vaccines by different types of healthcare professionals under real-world conditions and occur in settings where people may make different decisions about vaccination. The CDC is looking at how well COVID 19 vaccines work in different groups of people, such as essential workers, racial and ethnic minorities, and tribal nations. Studies are also looking at effectiveness in groups of people who are more likely to get COVID-19, as well as those who are more likely to get seriously ill if they get COVID-19.

So far, the VE studies have shown that the COVID vaccines are working well in real world settings offering similar protection at reducing the risk of COVID-19 by 90% or more. Most VE data currently available is related to the mRNA vaccines because these vaccines have been available longer. However, according to an August, 2021 study of South African health workers, the J&J vaccine showed 71% efficacy against hospitalization and 96% efficacy in preventing death from COVID-19. In addition to protecting against COVID 19, there is increasing evidence that COVID 19 vaccines also protect again asymptomatic COVID-19 infections.

Q: Is antibody testing recommended for accessing immunity to COVID-19 following vaccination?

A: Antibody tests for COVID-19 look for the presence of antibodies made in response to a previous infection or vaccination. They are an indicator of the body’s efforts to fight off the SARS-CoV-2 virus. None of the currently authorized SARS-CoV-2 antibody tests have been validated to evaluate specific immunity or protection from SARS-CoV-2 infection.

Antibody testing is NOT currently recommended to assess:

  • Immunity to COVID-19 following COVID-19 vaccination
  • The need for vaccination in an unvaccinated person

There are several issues to consider when interpreting an antibody test for SARS-CoV-2 infection:

  • Scientists have not yet established a serologic correlate of protection, which is the measurable threshold above which a person is protected against SARS-CoV-2 infection. This makes it difficult to interpret how laboratory results might translate to clinical protection.
  • Antibody testing does not evaluate the cellular immune response, which may also play a role in vaccine-mediated protection.
  • Vaccines trigger antibodies to specific viral protein targets. Currently authorized COVID-19 vaccines induce antibodies to the spike protein but not to the nucleocapsid protein, which is likely detected only after a natural infection with SARS-CoV-2. Therefore, COVID-19-vaccinated people who have not had previous natural infection will receive a negative antibody test result if the antibody test is designed to detect nucleocapsid protein.
  • Antibody tests have different levels of sensitivity (i.e., the true positive rate, or ability to identify people with antibodies to SARS-CoV-2) and specificity (i.e., the true negative rate, or ability to identify those without antibodies to SARS-CoV-2).

Q: I am fully vaccinated. Do I need a booster vaccine?

A: In general, a patient is considered fully vaccinated ≥2 weeks after a 2-dose mRNA COVID-19 vaccine series or ≥2 weeks after a single dose of J&J COVID-19 Vaccine.

Immunocompromised Individuals
The CDC recommends a third mRNA COVID-19 vaccine dose for people whose immune systems are moderately to severely compromised. This recommendation applies to immunocompromised people who originally received two mRNA COVID-19 vaccines, but not to those who received the J&J COVID-19 vaccine. CDC recommends the third dose be administered at least four weeks after a second dose of Pfizer-BioNTech COVID-19 vaccine or Moderna COVID-19 vaccine.

CDC recommendations apply to people who have:

  • Been receiving active cancer treatment for tumors or cancers of the blood.
  • Received an organ transplant and are taking medicine to suppress the immune system.
  • Received a stem cell transplant within the last two years or are taking medicine to suppress the immune system.
  • Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome).
  • Advanced or untreated HIV infection.
  • Active treatment with high-dose corticosteroids (i.e., ≥20mg prednisone or equivalent per day), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor-necrosis (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory.

The CDC recommends people talk to their health care provider about their medical condition, and whether getting an additional dose is appropriate for them. The CDC has recommendations for providers to use when talking with patients who are immunocompromised about a third dose of an mRNA vaccine.

Non-immunocompromised individuals
The CDC recommends a booster shot of the Pfizer-BioNTech COVID-19 vaccine in certain populations and also recommends a booster dose for those in high risk occupational and institutional settings. These recommendations only apply to individuals who completed the two-dose Pfizer-BioNTech COVID-19 vaccine series. Recommendations for individuals who received the Moderna or J&J vaccines will be forthcoming once additional data is available.

The CDC recommends:

  • People 65 years and older and residents in long-term care settings should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series.
  • People aged 50–64 years with underlying medical conditions should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series.
  • People aged 18–49 years with underlying medical conditions may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks.
  • People aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks.

According to the CDC, occupations at increased risk for COVID-19 exposure and transmission include front line essential workers and health care workers. The CDC previously identified the following groups in this category*:

  • First responders (healthcare workers, firefighters, police, congregate care staff)
  • Education staff (teachers, support staff, daycare workers)
  • Food and agriculture workers
  • Manufacturing workers
  • Corrections workers
  • U.S. Postal Service workers
  • Public transit workers
  • Grocery store workers

*List could be updated in the future

Q: Should asthma patients taking either inhaled corticosteroids or biologics or both consider themselves immunocompromised enough to consider early acquisition of third COVID vaccine?

A: The CDC doesn’t consider asthma or inhaled corticosteroids for asthma as leading to an immunocompromised state. There’s no data to suggest that biologics and/or inhaled corticosteroids have any effect (good or bad) on response to a COVID-19 vaccine including a booster injection. Only patients on daily oral corticosteroids of 20mg or more are considered immunocompromised by the CDC.

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. The emergence of variants with a higher transmission rate (higher R naught) will cause the percentage of the population who need to have immunity to increase.

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 everyone age 12 or older get a COVID 19 vaccination as soon as possible.

The College recognizes that COVID 19 vaccines are safe and effective at preventing COVID 19 disease, especially severe illness, hospitalizations, and death. And that COVID 19 vaccines reduce the risk of people spreading the SARS-CoV-2 virus. The efficacy of the vaccines clearly outweighs any risk associated with receiving the vaccines.

 

COVID-19 Vaccine FAQs

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