It’s been a few years since the first COVID-19 vaccines rolled out, and with the benefit of hindsight—and mountains of data—we can now answer one of the biggest questions of the pandemic: Were the mRNA COVID-19 vaccines safe and effective?
The short answer: Yes. Emphatically yes.
Let’s break it down.
A Major Scientific Breakthrough
The COVID-19 vaccines from Pfizer-BioNTech and Moderna used mRNA technology—a method that had been in development for decades but had never been used in an approved vaccine before. When COVID-19 hit, researchers were able to adapt this platform rapidly to target the virus, delivering vaccines that offered over 90% protection against symptomatic COVID-19 in early trials.
- Pfizer’s trial showed 95% effectiveness at preventing symptomatic infection (Polack et al., NEJM, 2020).
- Moderna’s results were similar, showing 94.1% effectiveness (Baden et al., NEJM, 2021).
These numbers held strong in the early months and, although they dropped somewhat with the arrival of new variants like Delta and Omicron, the vaccines remained highly effective at preventing severe illness and death—especially with booster doses (Thompson et al., MMWR, 2022).
What About Safety?
Safety was a top concern—and rightly so. Vaccinating billions of people requires high confidence. These vaccines went through large-scale clinical trials and were followed by some of the most intense safety monitoring in medical history.
Most people experienced only mild side effects—sore arms, tiredness, maybe a headache. A small number of cases of myocarditis (heart inflammation) occurred, mainly in young men after the second dose. But these cases were usually mild and far less common than heart complications caused by COVID-19 itself.
- Studies from the CDC and global health agencies showed the benefits far outweighed the risks (Rosenblum et al., JAMA, 2021; Mevorach et al., NEJM, 2021).
What’s mRNA and Is It Safe?
A lot of misinformation swirled around mRNA technology. But here’s the truth: mRNA doesn’t change your DNA. It’s like a text message that tells your cells how to build a harmless piece of the virus so your immune system learns to recognize it. Then it’s gone.
Scientists had been developing mRNA treatments for cancer and other infectious diseases long before COVID-19. The pandemic just fast-tracked its successful debut.
(Pardi et al., Nature Reviews Drug Discovery, 2018)
Pregnancy and Fertility: What the Research Found
There were early fears that COVID-19 vaccines might affect fertility or harm pregnancies. Those fears turned out to be unfounded.
- A study in the New England Journal of Medicine found no increase in miscarriage or other problems among vaccinated pregnant women (Shimabukuro et al., 2021).
- Other studies showed that vaccinated mothers passed protective antibodies to their babies, providing a double benefit (Gray et al., AJOG, 2021).
The Bottom Line: A Global Lifesaver
Billions of doses later, we can say with confidence that COVID-19 vaccines, especially the mRNA versions, were one of the most important scientific breakthroughs of our time.
- A 2022 study in The Lancet Infectious Diseases estimated that vaccines saved over 14 million lives in their first year alone (Watson et al., 2022).
These vaccines helped turn the tide of a once-in-a-century pandemic. They were not perfect. No vaccine is. But they were—and are—an extraordinary tool for saving lives and reducing suffering.
If you’re interested in how mRNA vaccines might help tackle diseases like cancer, flu, or RSV next, stay tuned. The future of medicine may be built on the same foundation that helped us through COVID-19.
