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How effective are COVID-19 vaccines?


vaccine effectiveness

FDA COVID-19 Vaccine Approval Considerations

On June 30, 2020 the U.S. Food and Drug Administration (FDA) stated that a COVID-19 vaccine would only receive approval if it were at least 50 percent more effective than a placebo at either preventing infection or reducing illness severity.1

The FDA released its guidance for industry regarding Emergency Use Authorization (EUA) approval for COVID-19 vaccines on October 6, 2020, and stated that it would be requiring that at least half of all Phase 3 clinical trial participants be followed for at least two months following administration of the second vaccine dose. The FDA also requested that vaccine manufacturers submit information on a minimum of five cases of severe COVID-19 disease among individuals who received the placebo.2

However, vaccine trial designs have faced criticism and in October of 2020 the British Medical Journal (BMJ) noted that Phase 3 trials for Moderna, Pfizer, AstraZeneca COVID-19 vaccines will not answer basic questions around preventing infection and reducing the likelihood of severe illness.3

A September 2020 article in Forbes by noted biologist William Haseltine, PhD4 revealed that COVID-19 vaccine studies by Moderna, Pfizer, AstraZeneca and Johnson & Johnson intend “to complete interim and primary analyses that at most include 164 participants.” 5

According to Dr. Haseltine, with an efficacy success requirement of 70 percent, this equates to interim analysis based on the results of infection ranging from 32 (Moderna) vaccine to 77 (Johnson & Johnson) vaccine recipients. Dr. Haseltine concluded by saying that COVID-19 vaccine trials were in essence designed to succeed. The article also contained many of the same concerns noted in the October 2020 BMJ article and added that “vaccines currently under trial will not be the silver bullet” ending the pandemic.6

As of February 27, 2021, there have been three COVID-19 vaccines authorized for use by the U.S. Food and Drug Administration (FDA) under Emergency Use Authorization (EUA).

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Durability of Vaccine Acquired Immunity

In February 2021, the CDC stated that currently available mRNA COVID-19 vaccines are believed to offer fully vaccinated individuals at least three months of vaccine-acquired immunity. In their quarantine guidance released on February 11, 2021, the CDC stated that fully vaccinated people (those who have received two doses of COVID-19 vaccine) who are exposed to SARS-CoV-2 through close contact are not required to quarantine as long as vaccination has occurred within three months and they remain asymptomatic.7

However, in March 2021 the CDC’s website stated that it is unknown how effective, or for what length of time experimental COVID-19 vaccines would provide immunity against COVID 19 illness. The website also reported that it is also unknown how effective the vaccine will be in mediating the severity of illness, should the vaccine fail to prevent COVID-19.8  

On April 27, 2021, fully vaccinated individuals were still being told that they must stay at least 6 feet apart from others; wear masks in certain outdoor crowded public settings and indoor public settings; and when in gatherings with unvaccinated individuals. Vaccinated individuals were also being told to take precautions when visiting unvaccinated individuals who are at an increased risk for severe COVID-19 disease and to be vigilant about symptoms and get tested when they occur. The CDC, however, stated that vaccinated individuals could travel domestically and internationally without quarantining, and that pre- and post- travel testing was not required, unless the international destination required it. Persons entering the U.S., however, were still required to show a negative COVID-19 test result before boarding a flight and testing was still advised 3-5 days following international travel.9

In May 2021, the CDC announced that fully vaccinated individuals could resume activities without masking or physically distancing, except where required by law, workplace or local requirements. Additionally, they could travel domestically without testing or self-quarantine, and travel internationally without testing unless their destination required it, and would not be required to self-quarantine on return. Vaccinated persons exposed to someone with SARS-CoV-2 were also advised that they would not need to self-quarantine or test unless symptomatic.10

Since emergency use of the experimental COVID-19 vaccines was authorized by the FDA in December 2020, there have been reports of fully vaccinated individuals testing positive for SARS-CoV-2. In late January 2021, Congressman Stephen Lynch of Massachusetts tested positive for the virus despite receiving the two recommended vaccine doses earlier in the month.11 Four individuals from Oregon also tested positive for the virus two weeks after receiving the second vaccine dose. Health officials reported their symptoms to range from none to mild.12

In early April 2021, Michigan health officials reported that between Jan 1 and March 31, 2021, at least 246 Michigan residents considered fully vaccinated against COVID-19 had tested positive for the virus, and three individuals had died.13

As of April 30, 2021, 10,262 cases of COVID-19 had been reported in fully vaccinated individuals, and included 995 hospitalizations, and 160 deaths. The CDC has acknowledged that the number of breakthrough cases is likely much higher since the reporting system is passive and voluntary, and relies on local and state health departments to provide this information.14

In late April 2021, the CDC announced that it was only going to be reporting the number of breakthrough cases that resulted in hospitalization and death “to help maximize the quality of the data collected on cases of greatest clinical and public health importance.”15 As a result, the public will not be made aware of the actual number of reported breakthrough cases occurring fully vaccinated individuals.

As of July 12, 2021, there have been 5,189 hospitalizations and 1,063 deaths in SARS-CoV-2 positive individuals who are reported to be fully vaccinated. The CDC reports that 1,456 (28 percent) of hospitalizations and 272 (26 percent) of deaths were not directly attributed to COVID-19.16

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Pfizer-BioNTech COVID-19 Vaccine

On December 11, 2020, the FDA issued an EUA for Pfizer-BioNTech’s messenger RNA (mRNA) COVID-19 Vaccine for use in persons 16 years of age and older.17

According to a press release issued by Pfizer-BioNTech on November 9, 2020, the efficacy rate of their COVID-19 vaccine was over 90 percent “at 7 days after the second dose” in trial participants who had no prior history of SARS-CoV-2 infection.18 It is not yet known how long vaccine-acquired immunity from the Pfizer-BioNTech vaccine will persist.19

In data submitted to the FDA, Pfizer-BioNTech reported that 170 cases of laboratory confirmed SARS-CoV-2 infections had occurred in clinical trial participants, with eight reported in the vaccine group, and 162 in the placebo group. However, clinical data also reported a category of disease referred to as “suspected COVID-19” illness. This category involved persons who had symptoms of COVID-19 but were not laboratory confirmed. In the Pfizer study, 3410 cases of suspected COVID-19 were reported, with 1,594 occurring in the vaccine group, and 1,816 in the placebo arm.20

In a published editorial, associate editor of the British Medical Journal (BMJ), Dr. Peter Doshi, questioned Pfizer-BioNTech’s efficacy data:21

“With 20 times more suspected than confirmed cases, this category of disease cannot be ignored simply because there was no positive PCR test result. Indeed this makes it all the more urgent to understand. A rough estimate of vaccine efficacy against developing covid-19 symptoms, with or without a positive PCR test result, would be a relative risk reduction of 19% (see footnote)—far below the 50% effectiveness threshold for authorization set by regulators. Even after removing cases occurring within 7 days of vaccination (409 on Pfizer’s vaccine vs. 287 on placebo), which should include the majority of symptoms due to short-term vaccine reactogenicity, vaccine efficacy remains low: 29% (see footnote).”

(Footnote - Calculations in this article are as follows:  19% = 1 – (8+1594)/(162+1816); 29% = 1 – (8 + 1594 – 409)/(162 + 1816 – 287). I ignored denominators as they are similar between groups.)22

Doshi also noted that clinical trials were not designed to determine whether the COVID-19 vaccine could stop transmission of the SARS-CoV-2 virus, and that evaluation of the impact of the vaccine on the reduction of hospitalizations and deaths should be performed. Clinical trial data also revealed that eight people who previously tested positive for SARS-CoV-2 were found to have confirmed, symptomatic COVID-19 illness post-vaccination. This included one person in the vaccine arm, and seven in the placebo group. These results may indicate that COVID-19 vaccines might not prevent reinfection in previously infected individuals. In addition, Doshi stated that false negative PCR test results would significantly decrease the vaccine’s efficacy, as well as that “suspected” COVID-19 cases may be due to other viruses.23

There is also insufficient data to support the use of Pfizer-BioNTech’s COVID-19 vaccine in persons who are positive for SARS-CoV-2 at the time of vaccination. In clinical trials, there was one case of COVID-19 illness in both the vaccine group and the placebo group in persons who were found to be positive for SARS-CoV-2 at baseline. Based on the limited data of this sub-population provided to the FDA by Pfizer-BioNTech, the vaccine efficacy in this population was reported at -7.1 percent (Confidence Ratio -8309.9, 98.6).24

While the FDA approved use of the experimental vaccine in 16 and 17-year-old individuals, in clinical trials, only 153 adolescents were enrolled, with 77 receiving the vaccine, and 76 receiving the placebo.25 In the spring of 2021, Pfizer-BioNTech began testing their product for use in children 12 to 15 years of age.26 According to a press release issued by Pfizer on March 31, 2021, the vaccine was reported to be 100 percent effective in this population, based on a study of 2,260 adolescents 12 to 15 years of age.27 On April 9, 2021, company officials announced that they had submitted a request to the FDA for approval of the vaccine for use in this population.28

On May 10, 2021, the FDA expanded the EUA granted Pfizer/BioNTech to distribute its experimental mRNA vaccine in the U.S. to include administration to children as young as 12 years old29 and the CDC’s ACIP voted to approve its use in this population on May 12, 2021.30

The approval for use in adolescents 12 to 15 years was based on a small clinical trial involving 2,260 teens, of which 1,131 received the vaccine and 1,129 received a saline placebo.31 According to data provided by the vaccine manufacturer, the vaccine was reported to be 100 percent effective at preventing COVID-19. In the clinical trial, there were no cases of COVID-19 in the vaccine arm and 18 cases in the placebo arm. There were no cases of severe COVID-19 illness or death reported among clinical trial participants.32

In late March 2021, phase 1/2/3 clinical trials of the Pfizer-BioNTech vaccine in infants and children 6 months to 11 years of age were initiated. According to the press release issued on March 31, 2021, “the study is evaluating the safety, tolerability, and immunogenicity of the Pfizer-BioNTech COVID-19 vaccine on a two-dose schedule (approximately 21 days apart) in three age groups: children aged 5 to 11 years, 2 to 5 years, and 6 months to 2 years.” 33    

Complete study data from the clinical trials are not currently available for review. Officials from Pfizer-BioNTech have stated that they will only begin to make the data public two years following completion of the study, though the experimental vaccine is in use within the general population.34

The Pfizer-BioNTech COVID-19 vaccine must be shipped and stored between -80ºC to -60ºC (-112ºF to -76ºF) and protected from light until ready to use.35 However, on February 25, 2021, the FDA announced that frozen undiluted vials of the Pfizer-BioNTech COVID-19 could also be transported and stored at temperatures typically found  in pharmaceutical freezers for up to 14 days.36 Mishandling of the vaccine during any step of the distribution process may result in an ineffective vaccine product.37 Temperature storage and shipping guidelines were updated again on May 19, 2021, which permitted undiluted, thawed vaccines to be stored at refrigerator temperatures, 2°C to 8°C (35°F to 46°F), for up to 1 month.38

Pfizer-BioNTech also reports its COVID-19 vaccine to be just as effective against the U.K.’s B.1.1.7(Alpha) variant of SARS-CoV-2 virus.39 However, preliminary data from a study conducted by the University of Cambridge has found the vaccine to be less effective against the South African B.1.351 (Beta) SARS-CoV-2 virus variant.40 In April 2021, researchers from Tel Aviv University reported findings of a small study on the effectiveness of the Pfizer-BioNTech vaccine against the B.1.351 (Beta) variant. The study, which was released prior to peer review, found that vaccinated people were eight times more likely to become infected with this SARS-CoV-2 variant than unvaccinated individuals.41 42

On February 25, 2021, company officials announced that they had begun evaluating the safety and effectiveness of a third dose of their COVID-19 vaccine. The study is aimed at learning more on the effects of a booster dose for currently circulating and newly emerging SARS-CoV-2 variants. Specifically, Phase 1 clinical trial participants would be offered a 30µg booster dose of the current vaccine 6 to 12 months after completing the two-dose vaccine series.43

Additionally, Pfizer-BioNTech reported that they were in discussions with the FDA and the European Medicines Agency regarding plans for a clinical study of variant specific vaccines, including a vaccine targeting the South African B.1.351 (Beta) variant.44

In early March 2021, a small exploratory study out of New York University’s Grossman School of Medicine found that persons already recovered from SARS-CoV-2 virus infection receiving one dose of the vaccine produced more neutralizing antibodies to defend against future SARS-CoV-2 infection in comparison to persons who have not been infected with the SARS-CoV-2 virus and who had received two doses of the vaccine. The exploratory study may indicate that vaccination of persons who have already experienced SARS-CoV-2 infection may only need one dose of the Pfizer-BioNTech experimental COVID-19 vaccine. The study’s author added that these findings needed to be confirmed in larger studies.45

In April 2021, Pfizer CEO Albert Bourla reported that a third vaccine dose would likely be needed within 12 months, and annual shots might also be necessary. Pfizer has also reported that studies have reported the vaccine to be 93.1 percent effective six months after the second dose is administered.46

Israeli health officials report the Pfizer-BioNTech COVID-19 vaccine to be 64 percent effective against the SARS-CoV-2 variant B.1.617 (Delta). Pfizer company officials have acknowledged waning effectiveness of two doses of the vaccine against this variant.47 In response, they have announced plans to submit data to the FDA by August 2021 for a booster dose to target the Delta variant. 48 As of July 8, 2021, federal health officials have stated that booster doses are not needed but that they plan to continue to monitor the data and advise the public as needed.49

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Moderna’s COVID-19 Vaccine

On December 18, 2020, the FDA issued an EUA for Moderna’s mRNA COVID-19 vaccine for use in persons 18 years of age and older.50

In a press release issued on November 16, 2020, Moderna announced that its experimental mRNA vaccine candidate showed a 94.5 percent efficacy against COVID-19. Company officials reported their first interim results found a total of 95 COVID-19 cases among trial participants, with 90 cases in the placebo group and five in the vaccine group. According to Moderna, no severe cases of COVID-19 occurred among the vaccine recipients while 11 severe cases occurred in the placebo group.51 52

There is insufficient data on the use of Moderna’s COVID-19 vaccine in persons who are positive for SARS-CoV-2 at baseline. In clinical trials, there were no cases of COVID-19 illness in persons who were determined to be positive for SARS-CoV-2 at baseline in the vaccine group, and only one case among the SARS-CoV-2 positive individuals at baseline who were part of the placebo group.53

Like the Pfizer-BioNTech COVID-19 vaccine trials, Moderna’s Phase 3 clinical trials were not designed to determine whether their vaccine could reduce the impact of COVID-19 illness by decreasing hospitalizations, intensive care stays, or death. Additionally, the vaccines were not studied to assess their ability to halt SARS-CoV-2 virus transmission. The durability of vaccine-acquired immunity is not known and there is limited data on its use in persons who are immunocompromised as well as in children and adolescents.54

Phase 2/3 clinical trials of the vaccine have begun in children and adolescents 12 through 18 years of age. Company officials must enroll a minimum of 3,000 adolescent trial participants to provide efficacy and safety data, and receive FDA approval for use in this population. Moderna’s goal is to ensure that the vaccine will be available for use in adolescents prior to the start of the 2021 school year.55

On March 16, 2021, Moderna announced that Phase 2/3 clinical trials had begun in infants and children ages 6 months to 12 years of age. According to company officials, clinical trials would “evaluate the safety, tolerability, reactogenicity and effectiveness of two doses of mRNA-1273 given 28 days apart” and involve approximately 6,750 U.S. and Canadian children between 6 months and less than 12 years of age.56

Moderna’s experimental COVID-19 vaccine must remain frozen between -25°C and -15°C (-13°F and 5°F) and thawed vaccines can’t be refrozen.57 Temperature control issues during product shipment have occurred, resulting in spoiled vaccines.58 59

Moderna reports that its COVID-19 vaccine appears to offer vaccine-acquired protection against the U.K’s B.1.1.7 (Alpha) variant. The vaccine, however, had a six-fold reduction against the South African B.1.351(Beta) variant when compared to the initial SARS-CoV-2 virus.60

On February 24, 2021, company officials announced that it had completed manufacturing of materials for a variant-specific vaccine targeting the South African B.1.351 variant. Additionally, Moderna stated that they were planning to move forward with two unique study strategies. 61

First, Moderna reported plans to evaluate three approaches to boosters. These include: clinical trials of a booster dose of a vaccine targeting the South African B.1.351 (Beta) variant; clinical trials of a multi-variant vaccine dose targeting the original SARS-CoV-2 virus and the South African B.1.351 variant; and clinical trials of a 50µg booster dose of the current vaccine. Second, company officials report plans to begin studies on the use of the vaccine candidate targeting the South African B.1.351 (Beta) variant dose and the experimental multi-variant vaccine dose as a primary vaccination series in individuals who are seronegative for SARS-CoV-2.62 Moderna announced on March 10, 2021 that booster dose administration had begun in participants as an amendment to the ongoing Phase 2 clinical study.63

In early April 2021, Moderna CEO Stéphane Bancel reported that a third vaccine dose would be needed within one year. In an interview with Business Insider, Bancel stated that "I hope this summer to get the vaccine authorized for a boost so that we can help people getting boosted before the fall, so that we all have a normal fall and not a fall and winter like we just saw in the last 6 months." Moderna officials have reported that the vaccine is 90 percent effective six months after the second vaccine dose.64

The CDC and FDA, however, issued a joint statement on July 8, 2021, reporting that a booster dose was not required at this time. Federal health official stated that they were monitoring the data and would inform the public on the use of booster doses as needed.65

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Efficacy of COVID-19 mRNA Vaccines

In Feb 2021, a study questioning the efficacy of COVID-19 vaccines expressed concerns regarding the absence of data on absolute risk reduction in the Pfizer-BioNTECH and Moderna COVID-19 vaccine clinical trials.66

According to this study, the Pfizer-BioNTech COVID-19 vaccine showed an absolute risk reduction of 0.7 percent (95% CI 0.59% to 0.83%) and the study author, Ronald Brown, reported that 142 people (95% CI 122 to 170) would need to be vaccinated to prevent one case of COVID-19. The Moderna COVID-19 vaccine showed an absolute risk reduction of 1.1 percent (95% CI 0.97% to 1.32%) and 88 individuals (95% CI 76 to 104) would need to be vaccinated to prevent one COVID-19 case.

Brown concluded by noting that:

“A critical appraisal of phase III clinical trial data for the Pfizer/BioNTech vaccine BNT162b2 and Moderna vaccine mRNA-1273 shows that absolute risk reduction measures are very much lower than the reported relative risk reduction measures. Yet, the manufacturers failed to report absolute risk reduction measures in publicly released documents. As well, the U.S FDA Advisory Committee (VRBPAC) did not follow FDA published guidelines for communicating risks and benefits to the public, and the committee failed to report absolute risk reduction measures in authorizing the BNT162b2 and mRNA-1273 vaccines for emergency use. Such examples of outcome reporting bias mislead and distort the public’s interpretation of COVID-19 mRNA vaccine efficacy and violate the ethical and legal obligations of informed consent.”

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Janssen/Johnson & Johnson Pharmaceutical COVID-19 Vaccine

On February 27, 2021, the FDA issued an EUA for Janssen/Johnson & Johnson’s experimental vaccine for use in persons 18 years of age and older.67

In clinical trials, the vaccine was 67 percent effective in preventing moderate to severe COVID-19 occurring at least 14 days after vaccination and 66 percent effective in preventing moderate to severe COVID-19 occurring at least 28 days after vaccination.68 The vaccine, however, was reported to be only 42 percent effective in persons over the age of 60 who have underlying health conditions.69

Janssen/Johnson & Johnson’s experimental vaccine, Ad26.COV2.S (or JNJ-78436725), is also a non-replicating viral vector vaccine that uses AdVac® and PER.C6® technologies.70 AdVac technology uses an adaptation of human Adenovirus 26 to transport the genetic code of the SARS-CoV-2 spike protein into the body to trigger an immune response.71 72 PER.C6 are proprietary cells owned by Janssen Pharmaceutical that were developed in 1985 from retinal cells of an 18-week-old aborted fetus.73

According to a press release issued on January 29, 2021 by the National Institutes of Health:74

“The investigational vaccine was reportedly 66% effective at preventing the study’s combined endpoints of moderate and severe COVID-19 at 28 days post-vaccination among all volunteers, including those infected with an emerging viral variant. Moderate COVID-19 was defined as laboratory-confirmed SARS-CoV-2 plus either one of the following: evidence of pneumonia; deep vein thrombosis; difficulty breathing; abnormal oxygen saturation or a respiratory rate equal to or greater than 20; or two or more signs or symptoms suggestive of COVID-19, such as cough, sore throat, fever or chills. Severe COVID-19 was defined as laboratory-confirmed SARS-CoV-2 plus evidence of clinical signs at rest indicative of severe systemic illness, respiratory failure, shock, significant organ dysfunction, hospital intensive care unit admission or death.

“Geographically, the level of protection for the combined endpoints of moderate and severe disease varied: 72% in the United States; 66% in Latin American countries; and 57% in South Africa, 28 days post-vaccination. The investigational vaccine was reportedly 85% effective in preventing severe/critical COVID-19 across all geographical regions. No deaths related to COVID-19 were reported in the vaccine group, while 5 deaths in the placebo group were related to COVID-19. Overall, there were 16 deaths in the placebo group, and 3 deaths in the vaccine group.”

Data is currently not available to determine how long the Janssen/Johnson & Johnson vaccine will provide protection, and there is no evidence that the vaccine prevents transmission of SARS-CoV-2 from person to person. 75

In February 2021, company officials reported that annual vaccine doses will likely be needed for several years.76 As of July 8, 2021, federal health officials have declined to recommend booster doses.77

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University of Oxford and AstraZeneca’s Viral Vector COVID-19 vaccine

Viral vectored vaccines genetically engineer live viruses, such as adenoviruses, to include the SARS-CoV-2 spike protein code. The engineered viruses are then used as a vector (delivery method) to get the altered genetic code inside the cell.  This stimulates the cell’s ribosome to produce SARS-CoV-2 protein antigen that is recognized by the immune system and triggers an immune response.78

The University of Oxford and AstraZeneca’s have developed a non-replicating viral vector vaccine that uses a chimpanzee adenovirus to express the SARS-CoV-2 protein.79

On January 29, 2021, the European Union approved the vaccine for use in individuals 18 years and older despite limited data to support its effectiveness in adults over the age 55 years. The University of Oxford and AstraZeneca’s COVID-19 vaccine is estimated to have an efficacy of about 60 percent.80 Health officials in Germany, however, are not recommending use of the vaccine in adults 65 years of age and older after concluding that there is not enough data to determine whether the vaccine is effective in this population.81

Health officials in South Africa halted use of the experimental AstraZeneca COVID-19 vaccine after it was found to be less than 25 percent effective against the B.1.351 variant, which is most common SARS-CoV-2 virus variant circulating in South Africa.82

On March 22, 2021, it was reported that the experimental vaccine was 79 percent effective. However, on March 23, 2021, Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases (NIAID) stated that AstraZeneca’s press release on their COVID-19 vaccine was misleading and contained outdated information. AstraZeneca was urged by NIAID to work with the Data and Safety Monitoring Board “to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible."83  

IMPORTANT NOTE: NVIC encourages you to become fully informed about covid-19 and the covid-19 vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

« Return to Vaccines & Diseases Table of Contents

Updated July 27, 2021

References

1 Weise E. FDA says a coronavirus vaccine would have to be at least 50% effective to be approved. USA Today July 1, 2020.

2 U.S. Food and Drug Administration. Emergency Use Authorization for Vaccines to Prevent COVID-19. May 25, 2021.

3 Doshi P. Will covid-19 vaccines safe lives? Current trials aren’t designed to tell us. BMJ October 2020; 371:m4037.

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6 Haseltine WA. Covid-19 Vaccine Protocols Reveal That Trials Are Designed To Succeed. Forbes Sept. 23, 2020.

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21 Doshi P. Peter Doshi: Pfizer and Moderna’s “95% effective” vaccines—we need more details and the raw data. The BMJ Opinion Jan. 4, 2021.

22 Doshi P. Peter Doshi: Pfizer and Moderna’s “95% effective” vaccines—we need more details and the raw data. The BMJ Opinion. Jan. 4, 2021.

23 Doshi P. Peter Doshi: Pfizer and Moderna’s “95% effective” vaccines—we need more details and the raw data. The BMJ Opinion Jan. 4, 2021.

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25 U.S. Food and Drug Administration. Vaccines and Related Biological Products Advisory Committee December 10, 2020 Meeting Briefing Document- FDA. Dec. 10, 2020.

26 Cáceres B. Moderna, Pfizer Test mRNA Experimental Biologics on Children. The Vaccine Reaction Feb. 7, 2021.

27 BusinessWire. Pfizer-BioNTech Announce Positive Topline Results of Pivotal COVID-19 Vaccine Study in Adolescents. Mar. 31, 2021.

28 Morrow B. Pfizer requests expansion of vaccine to adolescents, looks to start vaccinations before next school year. Yahoo News Apr. 9, 2021.

29 U.S. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Authorizes Pfizer-BioNTech COVID-19 Vaccine for Emergency Use in Adolescents in Another Important Action in Fight Against Pandemic. May 10, 2021.

30 Soucheray S. CDC advisers green-light COVID vaccine in young teens. CIDRAP News May 12, 2021.

31 U.S. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Authorizes Pfizer-BioNTech COVID-19 Vaccine for Emergency Use in Adolescents in Another Important Action in Fight Against Pandemic. May 10, 2021.

32 Perez J. Safety, immunogenicity and efficacy of BNT162b2 in persons aged 12-15 years. U.S. Centers for Disease Control and Prevention May 12, 2021.

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37 Cáceres B. Pfizer’s Experimental COVID-19 Vaccine 90 Percent Effective? The Vaccine Reaction Nov. 17, 2020.

38 U.S. Food and Drug Administration. FDA In Brief: FDA Authorizes Longer Time for Refrigerator Storage of Thawed Pfizer-BioNTech COVID-19 Vaccine Prior to Dilution, Making Vaccine More Widely Available. May 19, 2021.

39 Joseph A. Pfizer-BioNTech Covid-19 vaccine works just as well against variant first detected in U.K., study indicates. STAT News Jan. 20, 2021.

40 Kelland K. Study Suggests Pfizer's COVID-19 Vaccine Less Effective Against South African Variant. Medscape Feb. 4, 2021.

41 Attkisson S. STUDY: Vaccinated people more likely to be infected with Covid-19 variant. Apr. 16, 2021.

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44 Pfizer Pfizer And Biontech Initiate A Study As Part Of Broad Development Plan To Evaluate Covid-19 Booster And New Vaccine Variants. Feb 25, 2021.

45 NYU Langone Health News Hub. Patients Recovered from COVID-19 May Require Just One Dose of mRNA Vaccine. Mar. 9, 2021.

46 Ellis R. Pfizer, Moderna Say Booster Shots Probably Needed. WebMD News Brief Apr. 16, 2021.

47 McNamara D. Pfizer to Seek OK for COVID Vaccine Booster Targeting Delta. WebMD July 8, 2021.

48 McNamara D. Pfizer to Seek OK for COVID Vaccine Booster Targeting Delta. WebMD July 8, 2021.

49 U.S. Food and Drug Administration. Joint CDC and FDA Statement on Vaccine Boosters. July 8, 2021.

50 U.S. Food and Drug Administration. FDA Takes Additional Action in Fight Against COVID-19 By Issuing Emergency Use Authorization for Second COVID-19 Vaccine. Dec. 18, 2020.

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52 Dall C. Early data show Moderna's COVID vaccine 94.5% effective. CIDRAP News Nov. 16, 2020.

53 U.S Food and Drug Administration. Vaccines and Related Biological Products Advisory Committee December 17, 2020 Meeting Presentation- FDA Review of Efficacy and Safety of Moderna COVID-19 Vaccine EUA. Dec. 17, 2020.

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