Opinion: Covid-19 vaccines are safe. But let’s be clear about what ‘safe’ means

Unprecedented collaborative efforts in vaccine development have culminated in multiple vaccines being tested in advanced clinical trials all in less than one year since global leaders understood we were in the midst of a global pandemic. One is now being given to health care workers, and another will soon follow.

As the first Covid-19 vaccines are being distributed in the United States and in other countries around the world, the main question now on 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 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 every year. They are also one of the most thoroughly tested and safest products in history.

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


However, it’s important to be clear about what “safe” means. No vaccine — indeed, no medical treatment — is completely free from side effects. And it is the responsibility of medical professionals to be honest about them so people are prepared and more likely to trust the science.

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

The reasons vary from religious beliefs to centuries of medical exploitation inflicted on communities of color and to rampant misinformation on social media. On top of these, 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 go through a careful process in which it is tested in tens of thousands of volunteers. This system is set up to catch all but the rarest of side effects. Even after a vaccine is licensed, it is subject to stringent safety assessments to detect problems that arise when a vaccine is given to millions of people.

All of that complicates the ability of public health leaders to communicate that side effects and adverse reactions to the vaccine are normal, especially when such reactions become headlines, are amplified on social media, and become fodder 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 disorder that causes nerve damage. 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 near-daily briefings about the country’s vaccination campaign as a way to ease public concerns about the vaccine’s safety. The U.S. had learned its lesson the hard way: In 1976, an overwrought response to a small, contained swine flu outbreak led to many false stories about the side effects of a then newly developed swine flu vaccine.

In other cases, experts have determined that the risks of a particular vaccine were too costly to bear. Take RotaShield, the first vaccine developed to prevent rotavirus, a serious gastrointestinal disease in children. The vaccine was licensed in the U.S. in 1998. A year later, an investigation showed that the vaccine increased the risk of a rare intestinal obstruction by one to two cases per 10,000 infants vaccinated. Vaccinations were halted, and the manufacturer pulled the vaccine from the market.

This experience demonstrates the rigor of America’s vaccine safety and oversight processes and how quickly authorities act if there is a problem. Second-generation rotavirus vaccines were later licensed and deployed, and post-marketing safety evaluations found no increases in risk of intestinal obstruction.

To be sure, experiencing any adverse effect or developing a disease from a vaccine — something that is supposed to prevent disease — can be devastating for individuals and families and should never be taken lightly, even amid a global pandemic. But the overwhelming benefits of vaccines to individuals and society significantly outweigh the risks for adverse reactions.

Thanks to vaccines that make it through the stringent system of testing and approval, infectious diseases that once affected hundreds of thousands of people per year in the U.S. are now exceedingly rare or, in cases, like smallpox, polio, and rubella, are fully eradicated. The downside is that, once a disease is kept at bay by vaccination, we tend to let our guard down and lose sight of how critical vaccines are to keeping them that way.

Covid-19 is yet another instance in which the risk of not being vaccinated is far greater than the risk of side effects posed by the vaccine itself. Of the tens of thousands of people who have already been vaccinated, some have reported short-term symptoms like fever or aches, and a few have reported allergic reactions. Compare that to the virus itself, which has infected more than 70 million people globally and killed approximately 1.6 million — including more than 300,000 in the United States. That’s to say nothing of the devastation caused to economies and health systems around the world.

As the old adage goes, vaccines don’t save lives, vaccinations do. The only way to put a stop to this ongoing tragedy and get back to some semblance of normal is to have widespread vaccination campaigns. That starts with helping people understand — through regular public briefings and mass-media campaigns — that the Covid-19 vaccines are safe while being clear about potential side effects. It also requires complete, ongoing 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, achieve widespread 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 adjunct professor, in the Department of Epidemiology at the Harvard T.H. Chan School of Public Health. Michelle A. Williams is the dean of the Harvard T.H. Chan School of Public Health. Both are members of the Human Immunomics Initiative.

Source: STAT