Covid-19 vaccines are safe. It does not mean any side effects

youPrevious collaborative efforts in vaccine development have culminated in several vaccines being tested in advanced clinical trials, all in less than a year, since global leaders realized we were in the middle of a global pandemic. One is now being given to healthcare professionals and another is coming soon.

As the first Covid-19 vaccines are being distributed in the United States and other countries around the world, the main question now in many minds is: “Are these vaccines safe? “

The answer is yes.


Vaccines are one of the great modern triumphs of public health. They have helped to add several decades to human life expectancy and are one of the best tools for preventing disease, debilitation and death. Immunizations with childhood vaccines prevent 2 to 3 million deaths each year. They are also one of the most tested and safest products in history.

We know from recent clinical trials of the Pfizer / BioNTech and Moderna vaccines for Covid-19 that serious reactions are rare. And as these vaccines are distributed to millions, we will gain even more confidence in their safety and effectiveness through post-marketing studies.


However, it is important to make it clear what “insurance” means. No vaccine – in fact, no medical treatment – is completely free of side effects. And it is the responsibility of medical professionals to be honest about them, so that people are prepared and are more likely to trust science.

Skepticism about vaccines has existed since Edward Jenner first immunized an 8-year-old boy against smallpox in 1796.

The reasons range from religious beliefs to centuries of medical exploitation inflicted to communities of color and rampant misinformation on social media. In addition, Covid-19 vaccines are being developed, tested and approved at record speed.

Before a vaccine is approved for use by the general public, it must undergo a careful process in which it is tested on tens of thousands of volunteers. This system is configured to detect all but the most rare side effects. Even after a vaccine is licensed, it is subject to rigorous safety assessments to detect problems that arise when a vaccine is given to millions of people.

All of this complicates the ability of public health leaders to communicate that side effects and adverse reactions to the vaccine are normal, especially when those reactions become headlines, are amplified on social media and become food for conspiracy theories.

In 2009, for example, the H1N1 vaccine, also known as the swine flu vaccine, was associated with an extremely small risk of Guillain-Barré syndrome, a rare autoimmune disease that causes nerve damage. The researchers calculated that there were 1.6 extra cases of this syndrome among every 1 million people vaccinated. At the time, the CDC made clear communication a priority, holding almost daily briefings on the country’s vaccination campaign as a way to alleviate public concerns about the safety of the vaccine. The US learned the lesson the hard way: in 1976, an over-the-top response to a small, contained swine flu outbreak led to many false stories about the side effects of a newly developed swine flu vaccine.

In other cases, experts determined that the risks of a particular vaccine were too expensive to bear. Take RotaShield, the first vaccine developed to prevent rotavirus, a serious gastrointestinal disease in children. The vaccine was licensed in the United States in 1998. A year later, an investigation showed that the vaccine increased the risk of a rare intestinal obstruction in one to two cases per 10,000 vaccinated babies. Vaccination was suspended and the manufacturer withdrew the vaccine from the market.

This experience demonstrates the rigor of America’s vaccine surveillance and safety processes and the speed with which authorities act if there is a problem. Second-generation rotavirus vaccines were subsequently licensed and implanted, and post-marketing safety assessments found no increase in the risk of intestinal obstruction.

To be sure, experimenting any adverse effect or develop a disease from a vaccine – something that should prevents disease – can be devastating to individuals and families and should never be taken lightly, even in the midst of a global pandemic. But the huge benefits of vaccines for individuals and society significantly outweigh the risks of adverse reactions.

Thanks to vaccines that pass the rigorous testing and approval system, infectious diseases that previously affected hundreds of thousands of people each year in the United States are now extremely rare or, in cases like smallpox, polio and rubella, are completely eradicated. The disadvantage is that, once a disease is kept under control through vaccination, we tend to let our guard down and lose sight of how vaccines are essential to keep them that way.

Covid-19 is another case in which the risk of not being vaccinated is much greater than the risk of side effects caused by the vaccine itself. Of the tens of thousands of people who have already been vaccinated, some have reported short-term symptoms, such as fever or pain, and some have reported allergic reactions. Compare that to the virus itself, which infected more than 70 million people worldwide and killed approximately 1.6 million – including more than 300,000 in the United States. Not to mention the devastation caused to economies and health systems worldwide.

As the old saying goes, vaccines do not save lives, vaccines do. The only way to end this ongoing tragedy and return to some normal appearance is to have widespread vaccination campaigns. This starts by helping people to understand – through regular public briefings and mass media campaigns – that Covid-19 vaccines are safe and, at the same time, are clear about possible side effects. It also requires complete and continuous transparency by national, state and local government and public health officials as more data on these vaccines accumulate.

Only then will we begin to rebuild trust, obtain broad immunization and ensure that this virus survives only in our history books.

Wayne C. Koff is the president and CEO of the Human Vaccines Project and an adjunct professor in the Department of Epidemiology at Harvard TH Chan School of Public Health. Michelle A. Williams is dean of the Harvard School of Public Health TH Chan. Both are members of the Human Immunomics Initiative.