Vaccine Safety Research and Safety Studies

The United States’ long-standing vaccine safety system ensures vaccines are as safe as possible. As science advances and new information becomes available, this system will continue to improve.

Vaccine safety research:

  • Ensures the benefits of vaccines approved in the U.S. outweigh the risks.
  • Defines which groups should not receive certain vaccines.
  • Describes side effects and adverse events reported after vaccination.
  • Evaluates whether reported side effects and adverse events can be directly linked to a vaccine.

Vaccine Safety Publications

Access vaccine safety research conducted by CDC’s Immunization Safety Office (ISO) .

The Health and Medicine Division of the National Academies Reports on Vaccine Safety

Read summaries of vaccine safety reports by the Institute of Medicine.

Archive: The Immunization Safety Office Scientific Agenda

Learn about the development of ISO’s scientific and research agenda.

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Is the COVID-19 Vaccine Safe?

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Yes. The two mRNA vaccines, Pfizer and Moderna, authorized by the U.S. Food and Drug Administration (FDA) and recommended by the Centers for Disease Control and Prevention (CDC), are very safe and very good at preventing serious or fatal cases of COVID-19. The risk of serious side effects associated with these vaccines is very small.

Lisa Maragakis, M.D., M.P.H. , senior director of infection prevention, and Gabor Kelen, M.D. , director of the Johns Hopkins Office of Critical Event Preparedness and Response, answer questions about the safety of the COVID-19 vaccines.

COVID-19 Vaccine Safety — What We Know

Are there risks or safety concerns regarding the COVID vaccines?

To help catch risks or safety concerns, the CDC and FDA monitor possible safety issues with the COVID-19 vaccines. This ongoing work has led to revised recommendations for the Johnson & Johnson vaccine and information about rare side effects tied to the Pfizer and Moderna vaccines.

At Johns Hopkins Medicine, we offer Pfizer and Moderna vaccines throughout our vaccine clinics.

This review process continues to monitor vaccine safety. Potential risks of COVID-19 vaccines are reviewed and weighed against the benefits of protection that the vaccines offer as well as the known, serious risk of harm due to COVID-19.

What if I got a J&J vaccine? Should I worry about blood clots?

If you received a Johnson & Johnson vaccine more than three weeks ago, you do not need to watch for side effects related to blood clots.

If you received the J&J vaccine within the last three weeks, you should watch for possible symptoms of TTS and get medical help immediately if you have any of the following:

Is there a risk of an allergic reaction to a COVID vaccine?

According to the CDC, anyone who has a severe allergy (e.g., anaphylaxis) to any of the mRNA vaccine ingredients should not receive this vaccine . The CDC says people with allergies to certain foods, insects, latex and other common allergens can safely receive the COVID-19 vaccine. Those with a history of severe allergic reaction (anaphylaxis) to injectables or other vaccines should discuss the vaccination with their doctor, who can evaluate and assess their risk.

The COVID-19 Vaccines: What you need to know | Las vacunas anticovid-19: información imprescindible

How was the COVID-19 vaccine developed so quickly?

The relatively quick development of these vaccines does not mean safety measures were skipped. There are several reasons why the COVID-19 vaccines were developed faster than other vaccines:

What steps are taken to help make sure the COVID-19 vaccines are safe?

Safety is always a top priority as federal agencies work with vaccine manufacturers and independent scientific organizations to develop, study, authorize and approve new vaccines. Here are some of the steps taken for COVID-19 vaccines, as well as other vaccines:

Learn more from the CDC about the safety steps for the COVID-19 vaccine .

Demographics of the COVID-19 Vaccine Trials

Do I still have to wear a mask if I get a vaccine?

The CDC continues to monitor the spread of COVID-19 and makes recommendations for wearing face masks, both for those who are fully vaccinated as well as people who are not fully vaccinated.

The CDC also recommends that masks and physical distancing be required when going to a doctor’s office, hospital or long-term care facility, including all Johns Hopkins hospitals, care centers and offices.

Johns Hopkins Medicine’s mask safety guidelines have not changed, and we still require everyone to wear masks inside all of our facilities.

Can I get COVID-19 from the vaccine?

You cannot and will not get COVID-19 from any of the vaccines. The COVID-19 vaccines do not have any virus or other infectious material in them.

What about the safety of COVID-19 vaccination for diverse groups of people?

The FDA and other reviewers closely consider diverse populations and include them in the trials. The clinical trials for the first two COVID-19 vaccines included members of underrepresented minorities and older age groups, and people with conditions such as obesity, diabetes, and heart and respiratory conditions.

Does Johns Hopkins Medicine recommend that I get a COVID-19 vaccine?

Yes, we recommend that everyone who is eligible get vaccinated with one of the currently authorized mRNA COVID-19 vaccines: Pfizer or Moderna. We view both as highly effective in preventing serious disease, hospitalization and death from COVID-19 (including disease caused by the very contagious delta and omicron variants of the coronavirus), and we believe that their benefits outweigh their risks.

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COVID Omicron Variant: What You Need to Know

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Booster Shots and Third Doses for COVID-19 Vaccines

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COVID Natural Immunity: What You Need to Know

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COVID vaccines and safety: what the research says

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As people around the world receive COVID-19 vaccines, reports of temporary side effects such as headaches and fevers are rolling in. Much of this was expected — clinical-trial data for the vaccines authorized so far suggested as much. But now that millions of people are vaccinated, compared with the thousands enrolled in early studies, reports of some rare, allergic reactions are surfacing, and questions are arising about whether any deaths are linked to the shots.

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Nature 590 , 538-540 (2021)


With reporting from Smriti Mallapaty and Amy Maxmen.

Logunov, D. Y. et al. Lancet (2021).

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McNeil, M. M. et al. J. Allergy Clin. Immunol . 2 , T37–T52 (2016).

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News & Research

Covid-19 vaccine safety, study affirms overall safety of covid vaccine, dangers of infection.

Image of gloved hands administering a vaccine shot to an arm

Image: Chaz Bharj. iStock/Getty Images Plus 

Over the past year, results from a series of clinical trials have demonstrated the efficacy and safety of COVID-19 vaccines in preventing serious illness, hospitalizations, and deaths.

Yet, with sporadic reports of rare adverse events, one question has remained unanswered: Just how safe are COVID-19 vaccines in the real world, outside of clinical trials?

Get more HMS news here

Now, a study published Aug. 25 in The New England Journal of Medicine by researchers from Clalit Research Institute in Israel, Harvard Medical School, and the Harvard T.H. Chan School of Public Health answers that question.

The research, which assessed the safety of the Pfizer/BioNTech BNT162b2 mRNA vaccine, is based on analysis of data from nearly 2 million individuals in Israel and represents one of the largest real-world assessments of COVID-19 vaccine safety to date.

The findings, the researchers said, affirm the overall safety of the vaccine and underscore that the risk of adverse consequences from actual infection with SARS-CoV-2 far outweighs potential vaccine risks.

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The study involved two analyses: A comparison of adverse events between vaccinated and unvaccinated individuals, and between unvaccinated people infected with SARS-CoV-2 and unvaccinated noninfected people.

The study showed that few adverse events were associated with the vaccine. Myocarditis, or inflammation of the heart muscle, the most serious of them, was rare, with a rate of 2.7 excess cases per 100,000 vaccinated people. This means that for every 100,000 individuals, 2.7 more cases of myocarditis occurred than would be expected, the researchers said.

By contrast, the risk of myocarditis was notably higher among infected but unvaccinated individuals, occurring at a rate of 11 excess cases per 100,000 people.

Coronavirus infection—but not vaccination—was also associated with greatly increased risk of pericarditis (an inflammation of the area around the heart), heart arrhythmias, heart attacks, strokes, pulmonary embolism, deep-vein thrombosis, acute kidney damage, among others.

Vaccine hesitancy

“ To date, one of the main drivers of vaccine hesitancy has been a lack of information regarding potential side effects of the vaccine,” said study co-author Ben Reis, HMS assistant professor of pediatrics at Boston Children’s Hospital and director of the predictive medicine group in the Computational Health Informatics Program at Boston Children’s .

“This careful epidemiological study provides reliable information on vaccine safety, which we hope will be helpful to those who have not yet decided about vaccination, ” Reis said. 

“ Those who have hesitated until now to get vaccinated due to concerns about very rare side effects, such as myocarditis, should be aware that the risks for this very same side effect are actually higher among unvaccinated infected individuals,” Reis said.

The results are based on records from Clalit Health Services in Israel, one of the world’s largest integrated health record databases. The analysis is the largest peer-reviewed evaluation of the safety of a COVID-19 vaccine in a nationwide mass-vaccination setting.            

“The extensive nationwide rollout of Israel’s COVID-19 vaccination campaign provided the Clalit Research Institute with a unique opportunity to assess, through its rich and comprehensive digital datasets, the safety of the vaccine in a real-world setting, without needing to rely on individual-driven active reporting of side effects” said study senior author Ran Balicer, director of the Clalit Research Institute and Chief Innovation Officer for Clalit.

“These results show convincingly that this mRNA vaccine is very safe and that the alternative of ‘natural’ morbidity caused by the coronavirus puts a person at significant, higher, and much more common risk of serious adverse events,” Balicer said.

The results of this real-world study confirm, complement, and build on the previously reported findings of the Pfizer/BioNTech phase 3 randomized clinical trial, which involved 21,720 individuals, the researchers noted.

The comprehensive nature of this new analysis and the sheer volume of data involved offer a more detailed assessment of the vaccine’s safety across a wider range of adverse events.

“These data should facilitate informed individual risk-benefit decision-making, and, in our view, make a strong argument in favor of opting in to get vaccinated, especially in countries where the virus is currently widespread,” added Balicer, who also serves as chairman of Israel’s National Expert Advisory Team on COVID-19 response.

Previous efforts to characterize vaccine safety have relied on voluntary active reporting by vaccinated individuals, known to be incomplete. The new study relies on the analysis of millions of anonymized electronic medical records, which are far more comprehensive.

Parallel analyses

In an effort to provide the proper context that is critical for interpreting vaccine safety findings, the researchers also examine a wide range of adverse events both among vaccinated individuals and among unvaccinated individuals who were infected with the coronavirus, conducting two parallel analyses, assessing the occurrence of 25 adverse events in each of these groups.

In the vaccinated subgroup, the researchers compared the outcomes of 884,828 vaccinated individuals 16 years and older with those of 884,828 unvaccinated individuals based on an extensive set of sociodemographic, geographic, and health-related characteristics.

This analysis took place from Dec. 20, 2020, the launch of Israel’s national vaccination campaign, through May 24, 2021.

Some individuals switched groups based on their changing vaccination status, with 235,541 people moving from the unvaccinated group into the vaccinated group during the study.

To provide context for the vaccine safety findings above, a separate analysis was conducted among unvaccinated individuals. This analysis estimated rates of the same 25 potential adverse events among 173,106 unvaccinated individuals who were infected with SARS-CoV-2, compared with 173,106 carefully matched controls not infected with SARS-CoV-2.

This analysis took place from March 1, 2020, the beginning of the COVID-19 pandemic in Israel, through May 24, 2021.

The vaccine was found to be safe: Out of 25 potential side effects examined. four were found to have a link with the vaccine.

Myocarditis, an inflammation of the heart muscle associated with the vaccine was rare—2.7 excess cases per 100,000 vaccinated individuals. These events were observed mainly among males between the ages of 20 and 34.

In contrast, myocarditis was far more common among unvaccinated individuals infected with SARS-CoV-2. The analysis showed 11 excess cases of myocarditis per 100,000 infected individuals.

Other adverse events moderately associated with vaccination were swelling of the lymph nodes, a mild side effect that is part of a standard immune response to vaccination, with 78 excess cases per 100,000, appendicitis with 5 excess cases per 100,000, likely as a result of swelling of lymph nodes around the appendix.

Reactivation of dormant herpes zoster (chickenpox virus) infection occurred in 16 cases per 100,000.

Unvaccinated risks

These small numbers of adverse events among vaccinated individuals stood in stark contrast with the high rate of multiple and more serious adverse events among unvaccinated individuals infected with SARS-CoV-2.

These included cardiac arrhythmias (a 3.8-fold increase above baseline risk with 166 cases per 100,000 infected patients); kidney damage (14.8-fold increase with 125 excess cases per 100,000); pericarditis (5.4-fold increase with 11 excess cases per 100,000); pulmonary embolism (12.1-fold increase with 62 excess cases per 100,000); deep-vein thrombosis, or a blood clot in the veins (3.8-fold increase with 43 excess cases per 100,000); myocardial infarction, or heart attack (4.5-fold increase with 25 excess cases per 100,000); and stroke (2.1-fold increase with 14 excess cases per 100,000).

Additional investigators on the study included Noam Barda, Noa Dagan, Yair Ben-Shlomo, Eldad Kepten, Jacob Waxman, Reut Ohana, all of the Clalit Research Institute; Doron Netzer of Clalit Health Services; Miguel Hernán and Marc Lipsitch of the Harvard T.H. Chan School of Public Health; and Isaac Kohane of Harvard Medical School.

The research was funded in part by the newly announced Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.

Relevant disclosures: Marc Lipsitch receives support from the Morris-Singer Fund.

Disclosure forms  provided by the authors are available with the full text of this article at

Adapted from a Clalit Research Institute news release

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Vaccine Research & Development

How can covid-19 vaccine development be done quickly and safely, typical vaccine development timeline.

Accelerated timeline in a pandemic

Typical Timeline

A typical vaccine development timeline takes 5 to 10 years, and sometimes longer, to assess whether the vaccine is safe and efficacious in clinical trials, complete the regulatory approval processes, and manufacture sufficient quantity of vaccine doses for widespread distribution.

to the Accelerated Timeline

Preclinical Trials

Preclinical testing of vaccine candidates typically starts in animal models, first in small mammals such as mice or rats and then non-human primates such as monkeys. Preclinical studies are important for eliminating potential vaccines that are either toxic or do not induce protective immune responses. But many vaccines that appear to be safe and induce protective immune responses in animals fail in human studies. Only vaccine candidates that are very promising in preclinical testing move forward into phase I clinical trials.

Phase I Clinical Trials to Assess Safety, Dosing, and Immune Responses

Phase I clinical trials are the first step in assessing vaccines in people. Typically involving one to several dozen healthy volunteers, phase I trials assess short-term safety (e.g., soreness at the site of injection, fever, muscle aches) and immune responses, often with different vaccine dosages. Only if a vaccine candidate is shown to be safe in phase I trials will it move to larger phase II trials.

Phase 1 trials can be completed in two to three months, allowing for two doses of a vaccine three to four weeks apart

Phase II Clinical Trials to Assess Safety and Immune Responses

Phase II clinical trials continue to assess safety and immune responses but in a larger number and more diverse group of volunteers, typically one to several hundred people. Phase II trials may include target populations of a specific age or sex, or those with underlying medical conditions. Vaccines for children start with adult volunteers and move to progressively younger groups of children. Different types of immune responses are often measured, including antibodies and cell-mediated immunity, but phase II trials do not assess how well a vaccine actually works. Only in phase III trials is vaccine efficacy assessed.

Phase 2 trials can be completed in three to four months, allowing for longer follow-up to better assess safety and immunogenicity. This timeline is shortened when phase 1 and phase 2 trials are combined.

Phase III Clinical Trials to Assess Safety and Efficacy

Phase III clinical trials are critical to understanding whether vaccines are safe and effective. Phase III trials often include tens of thousands of volunteers. Participants are chosen at random to receive the vaccine or a placebo. In Phase III, participants and most of the study investigators do not know who has received the vaccine and who received the placebo. Participants are then followed to see how many in each group get the disease. Assessing short- and long-term safety is also a major goal of phase 3 trials.

Phase 3 trials may take six to nine months to allow early assessment of safety and efficacy, particularly if conducted in areas with a high risk of infection, but with follow-up continuing for two years or more to assess long-term safety and efficacy.

Regulatory Approval Process

Each country has a regulatory approval process for vaccines. In the United States, the Food and Drug Administration (FDA) is responsible for regulating vaccines. In situations when there is good scientific reason to believe that a vaccine is safe and is likely to prevent disease, the FDA may authorize its use through an Emergency Use Authorization (EAU) even if definitive proof of the efficacy of the vaccine is not known, especially for diseases that cause high mortality.

Scaling Up Vaccine Manufacturing

Scaling up vaccine manufacturing is typically done near the end of the regulatory process because of the huge financial investment needed. In the United States, the FDA will inspect the manufacturing facilities. The cost of developing a new vaccine can be several billion U.S. dollars prior to the scale up of manufacturing facilities.

Post-Licensure Vaccine Safety Monitoring

After a vaccine is approved and in widespread use, it is critically important to continue to monitor vaccine safety. Some very rare side effects may only be detectable when large numbers of people have been vaccinated. Safety concerns that are discovered at this late stage could lead a licensed vaccine to be withdrawn from use, although this is very rare.

research on vaccine safety

Article misleads on safety of Pfizer vaccine ingredient

An article and social media posts claim an ingredient in pfizer's covid-19 vaccine is not safe for humans, citing a data sheet from a us chemical corporation. this is misleading; the company says it does not manufacture the compound in the shot -- and the document pertains to research-grade chemicals, which health experts say do not undergo the same strict regulatory approval process..

"The package insert for Pfizer Inc's mRNA vaccine reveals the drug contains an ingredient listed as '[n]ot for human or veterinary diagnostic or therapeutic use in a technical data sheet referencing the US Occupational Safety and Health Administration (OSHA),'" says a February 7, 2023 article .

The article goes on to conflate the vaccine ingredient with a compound that Cayman Chemical , an American biotechnology company, produces for health research.

research on vaccine safety

Screenshot of an article taken February 15, 2023

The report comes from American Faith, a website founded by Phil Hotsenpiller , a pastor in the US state of California. His site has previously promoted debunked claims about Covid-19 treatments and vaccines .

The article's claim, examples of which date back to at least 2022, spread quickly on social media platforms such as Instagram and Twitter . But the Pfizer vaccine ingredient is not the same as Cayman Chemical's compound.

"We do not make ALC-0315 for pharmaceutical use," said Ryan Foster, a Cayman Chemical spokesperson, in a February 15 email.

What is the ingredient?

ALC-0315 is part of a lipid nanoparticle that helps shield the fragile messenger RNA (mRNA) molecules that Pfizer's Covid-19 vaccine delivers to cells.

"The RNA vaccine can't just be injected into the body, then it would break down immediately. It must be protected with a cover," Annette Beck-Sickinger , professor of biochemistry and bioorganic chemistry at the University of Leipzig in Germany, previously told AFP. "This shell is a mixture of different lipids (fat molecules), which then form small globules like a kind of 'soap bubble.'"

Fact sheets from the US Food and Drug Administration (FDA), the Public Health Agency of Canada and the European Medicines Agency (EMA) list ALC-0315 as a component of the Pfizer-BioNTech Comirnaty vaccine .

research on vaccine safety

This screenshot taken February 24, 2023 shows the Pfizer Covid-19 vaccine ingredient list on the FDA's website

"The manufacturing process and controls for Comirnaty have been well characterized and qualified," the FDA told AFP in a February 21 email. "The analytical procedures include tests to ensure vaccine safety, identity, purity, quality and potency."

A Pfizer spokeswoman told AFP she would not comment on non-Pfizer documents, instead pointing to the EMA fact sheet when asked about the safety of specific ingredients.

Cayman Chemical's compound

A safety data sheet from Cayman Chemical does say its ALC-0315 product is "for research use" and "not for human or veterinary diagnostic or therapeutic use."

research on vaccine safety

Screenshot of a Cayman Chemical safety data sheet taken February 16, 2023

But Raymond Tellier , a microbiologist at the McGill University Health Center in Canada, said it is important to note the other ingredients listed in the compound.

In addition to ALC-0315, the document shows the Cayman Chemical product is comprised of 95 percent ethanol , a volatile, flammable and toxic compound.

research on vaccine safety

Screenshot of a Cayman Chemical safety data sheet taken February 23, 2023

Tellier said that because lipids may not be water soluble, companies "dissolve them in an organic solvent."

"In the case of Cayman Chemical, they choose ethanol," he said in a February 16 email. "But in the final formulation of the vaccine, there is no ethanol."

In 2021, Cayman Chemical addressed similar misinformation about another compound that academics and scientists use to research health therapies.

"Chemicals under the same name can have differing designations such as grade or formulation that are defined by their manufacturing protocols and intended use," the company said in a press release.

Tellier said that is an important distinction.

"What they say is that their product 'is not for human or veterinary diagnostic or therapeutic use,'" he said. "The reason is simply that Cayman Chemical manufactures reagents for research labs and sells only to research labs; if you want to sell for other uses such as diagnostic or therapeutic uses there are many more regulatory and safety procedures to go through."

Companies that manufacture active pharmaceutical ingredients in the US must adhere to strict federal guidelines to ensure their safety for human and veterinary use. The Paul-Ehrlich-Institut , which regulates vaccines in Germany, has also addressed the difference between laboratory and pharmaceutical ingredients on its website.

All of AFP's reporting on vaccine misinformation is available here .

research on vaccine safety

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SMRT files police report after boy allegedly caused train delay by jamming screen door

SMRT filed a police report on a boy after he allegedly caused a train delay by jamming platform screen doors at Jurong East MRT station.

Wagner chief calls on Zelenskiy to abandon ‘encircled’ Bakhmut

Yevgeny Prigozhin says his troops are fighting against old men and children in besieged eastern Ukraine town

3 Singapore Blue-Chip Stocks Doubling Their Dividends in 2023

News of a dividend increase is always music to an investor’s ears. Here are three stocks that doubled their dividend payments. The post <strong>3 Singapore Blue-Chip Stocks Doubling Their Dividends in 2023</strong> appeared first on The Smart Investor.


  1. Coronavirus: How vaccines are developed and tested

    research on vaccine safety

  2. Vaccine Safety

    research on vaccine safety

  3. How to ensure that vaccines are safe

    research on vaccine safety

  4. Graphic Series on Vaccine Safety Questions

    research on vaccine safety

  5. » Immunizations

    research on vaccine safety

  6. The ethics of conducting clinical trials in the search for treatments and vaccines against COVID

    research on vaccine safety


  1. Way to second dose covid vaccine / Security Forces Medical Complex

  2. Fact check: Covid vaccines work, they are safe and are stopping transmission


  4. 'Censored': Dr. Kerryn Phelps reveals severe COVID-19 vaccine injuries

  5. Covid Vaccines: SAFE & effective... right?

  6. CDC's Tom Shimabukuro on COVID Vaccines


  1. Vaccine Safety Research and Safety Studies

    Vaccine Safety Research and Safety Studies The United States’ long-standing vaccine safety system ensures vaccines are as safe as possible. As science advances and new information becomes available, this system will continue to improve. Vaccine safety research: Ensures the benefits of vaccines approved in the U.S. outweigh the risks.

  2. Is the COVID-19 Vaccine Safe?

    From December 2020 to December 2021, about 470 million doses of COVID-19 vaccine have been given in the U.S. Roughly 12 months of data, including data from tens of thousands of participants in clinical trials, show that the vaccines are safe and effective at preventing serious disease or death due to COVID-19.

  3. COVID vaccines and safety: what the research says

    It is clear that coronavirus vaccines are safe and effective, but as more are rolled out, researchers are learning about the extent and nature of side effects. Ariana Remmel Older people have...

  4. COVID-19 Vaccine Safety

    The research, which assessed the safety of the Pfizer/BioNTech BNT162b2 mRNA vaccine, is based on analysis of data from nearly 2 million individuals in Israel and represents one of the largest real-world assessments of COVID-19 vaccine safety to date.

  5. Vaccine Research & Development

    Phase I clinical trials are the first step in assessing vaccines in people. Typically involving one to several dozen healthy volunteers, phase I trials assess short-term safety (e.g., soreness at the site of injection, fever, muscle aches) and immune responses, often with different vaccine dosages.

  6. Article misleads on safety of Pfizer vaccine ingredient

    An article and social media posts claim an ingredient in Pfizer's Covid-19 vaccine is not safe for humans, citing a data sheet from a US chemical corporation. This is misleading; the company says it does not manufacture the compound in the shot -- and the document pertains to research-grade chemicals, which health experts say do not undergo the same strict regulatory approval process."The ...