For more than a year, most of the world has been outmatched by Covid. Now we have a powerful tool that’s the only way out of the pandemic: vaccines.

Covid vaccines were a true breakthrough, the result of dazzling scientific progress, substantial investment, and some plain old good luck. The vaccines are safe and more effective than many public health professionals dared to hope early in the pandemic. Covid vaccines were ready quickly, but they weren’t rushed — no corners were cut on safety in the development of these vaccines. Massive investment and more than 20 years of research on mRNA technology got us to where we are now.

Although vaccination can help us gain the upper hand against the virus, we still face some big challenges. First and foremost is lack of access — there’s simply not enough vaccine to meet global demands, and, tragically, we’re facing a dry patch in the coming months, just as the disease is roaring back in many parts of the world.

Supply has been concentrated in a small number of wealthy countries, leaving low- and middle-income countries behind. We must urgently step up global production of vaccines⁠ — especially mRNA vaccines⁠ — because uncontrolled spread anywhere in the world is a risk everywhere.

In the U.S., we have plenty of supply and most (63%) adults have now been vaccinated with at least one dose, but there’s still a lot of work to do to reach those still unvaccinated. Covid case counts are falling — and the more people we vaccinate, the fewer clusters and outbreaks we will see in the coming months.

Expanding access to vaccination will go a long way toward reaching the unvaccinated, but we also have to address the questions and concerns that are holding some people back. It’s normal to have questions, and we should treat everyone who has questions with respect. That means meeting people where they are, listening to their concerns, and doing our best to respond to them. These five facts about Covid vaccines could (hopefully) make the choice to get vaccinated easier for you or a loved one, friend, or acquaintance.

1. The risks of infection are vastly higher than the risks of vaccination. Even healthy young people can become severely ill, die, or suffer long-term harm from Covid infection. Many people are struggling with “long Covid” symptoms such as fatigue, brain fog, headaches, loss of taste and smell, shortness of breath, joint or muscle pain, depression and anxiety, and more. Our team just published a deep dive into what we know about long Covid.
2. Covid vaccines don’t stay in your body. The vaccines prime your system to fight the virus and then disappear. In contrast, if you get Covid, the virus will spread throughout your entire body, make billions of copies, and stay there for at least a week.
3. Nearly every doctor who has been offered a Covid vaccine got it as soon as they could. Doctors and health care providers have a solid understanding of the science behind the vaccines, and many were deeply impacted by caring for Covid patients who became very ill or died.
4. The more of us who get vaccinated, the faster we can get back our jobs and our economy. Places with less vaccine coverage face a higher risk of Covid clusters and possibly outbreaks — especially with the spread of more contagious variants — which will result in continued disruption to society.
5. Vaccinations can save the lives of at least 100,000 Americans in the coming months who would otherwise be killed by Covid-19. They’ve already saved the lives of tens of thousands of people, many of them in nursing homes. We’ve tragically lost so many people already; we must do whatever we can to prevent even more deaths.

The vast majority of Americans who are hospitalized or dying from Covid right now are unvaccinated. Sadly, the virus reached them before the vaccine could. With the reduced spread of disease in almost every state and community in recent weeks, now is the time to get as many more people vaccinated as quickly as we can — before the virus has a chance to catch back up.

5 Facts About Covid Vaccines was originally published in Medium Coronavirus Blog on Medium, where people are continuing the conversation by highlighting and responding to this story.

After receiving a Covid-19 vaccine, many people may experience minor adverse effects such as fatigue or headaches, which generally last around 24 to 48 hours. These reactions can be a sign that the immune system is working and responding to the vaccine. But what does this say about (or to) people who do not experience any side effects? Does an absence of adverse effects mean the vaccine did not work?

Because adverse reactions to the vaccine are more likely to be reported, some people who have not experienced side effects may be worried that they are not as protected as those who did.

Epidemiologist and associate professor at the Johns Hopkins Bloomberg School of Public Health Dr. David Dowdy explained that “Some people are going to feel that pain much more strongly than others, but it doesn’t mean that those who didn’t feel the pain didn’t get the effect… It’s much more about how people’s bodies are attuned to what their immune system is doing.”

In short, “The people who don’t have those reactions are still very protected,” Dowdy said.

Scientists distinguish two types of adverse effects after vaccines: local reactions that occur at the site of injection — pain, swelling, or redness — and systemic reactions or symptoms felt throughout the rest of the body, such as fatigue, fever, or nausea. Both types may be caused by activation of the inflammatory immune system and typically go away within one to three days after vaccination.

Not everyone who receives a Covid-19 vaccine experiences side effects. In fact, during clinical trials, just over 50% of participants didn’t experience any side effects at all.

The U.S. Centers for Disease Control and Prevention (CDC) summarized the proportion of people who reported local and systemic side effects during the trials for the Moderna, Pfizer, and Johnson & Johnson/Janssen vaccines in adults. The most commonly reported systemic side effects were fatigue and headache, which were reported by as many as 50%–60% of mRNA vaccine recipients and 30%–45% of Janssen vaccine recipients.

Fever was less commonly reported. Among older age groups in the vaccine trials, only 3% of Janssen vaccine recipients and 10%–11% of mRNA vaccine recipients reported having a fever. Among younger age groups, the percentage was slightly higher for all three vaccines — at about 15%–18% of vaccine recipients.

During clinical trials, systemic side effects were more likely to be reported by younger people. Overall, about 80% of younger trial participants and 70% of older participants who received mRNA vaccines reported at least one systemic side effect. For the Janssen vaccine, 62% of younger and 45% of older participants w reported at least one systemic side effect.

For the mRNA vaccines, systemic side effects were more likely to be reported after the second dose than the first.

The immune system is complex and has many components. Some parts cause the short-term side effects that many people experience after vaccination, while other parts, collectively known as the “adaptive immune response,” provide the long-term protection against Covid-19.

The adaptive immune response takes time to develop — which is why people are not considered fully vaccinated until two weeks after the second dose of an mRNA vaccine or the single Janssen vaccine dose. This system includes antibodies and memory immune cells (memory B cells) that kick into action when they recognize a specific pathogen such as the SARS-CoV-2 virus.

According to Chris Thompson, PhD, an immunologist and associate professor of biology at Loyola University Maryland’s department of biology, a person’s reaction to vaccination “really boils down to the innate differences in each person’s biochemical makeup, environment, and personal history.”

For those who do experience side effects after the vaccine, the CDC has provided recommendations to minimize discomfort, as well as guidelines on how to tell when they might be more serious.

The bottom line? Most people who get vaccinated don’t have severe side effects, and they are well protected against Covid. Even if you feel just fine after the vaccine, you’re likely to be well protected. In this case, the dictum, “No pain, no gain” simply doesn’t apply.

Did Your Covid-19 Vaccine Work if You Didn’t Have Side Effects? was originally published in Medium Coronavirus Blog on Medium, where people are continuing the conversation by highlighting and responding to this story.