COVID-19 vaccinated individuals can and do get ill. Vaccines are not 100% effective at preventing infection, and breakthrough cases (infections in vaccinated people) have been common, especially with evolving variants like Omicron and its descendants. However, strong evidence shows vaccination significantly reduces the risk of severe illness, hospitalization, and death. Some rare side effects also occur, which can cause illness in a small subset of recipients.
Breakthrough Infections and Reduced Severity
No vaccine eliminates infection risk entirely. Early mRNA vaccines (Pfizer, Moderna) showed high initial efficacy (~95% against ancestral strains in trials), but real-world effectiveness against infection dropped with variants and time. Breakthrough cases became widespread by 2021–2022.
Data from states and countries illustrate this:
- In New York, over 2.8 million breakthrough cases occurred among fully vaccinated people (about 19% of the vaccinated population 5+), with hospitalizations at ~0.81%.
- Early reports (e.g., 2021) showed breakthrough hospitalizations and deaths were rare (<1% in many states), and mostly in those with comorbidities.
Vaccination still provides strong protection against severe outcomes. Recent 2024–2025 vaccines showed ~40% effectiveness against hospitalization and up to 79% against invasive mechanical ventilation or death in one case-control study. Updated vaccines continue to reduce hospitalizations by 46–72% in various analyses.
Why breakthroughs happen: Waning immunity over months, variant immune escape (e.g., Omicron sublineages), and individual factors like age, comorbidities, or immunosuppression. Vaccinated people can shed and transmit the virus during infection, though often for shorter durations with lower infectious virus loads in some studies.
Vaccine Side Effects Causing Illness
Vaccines can cause temporary side effects (sore arm, fatigue, fever, headache) in many people—these are normal immune responses and usually resolve quickly.
Rare serious adverse events:
- Myocarditis/pericarditis: Confirmed rare link, especially with mRNA vaccines (Pfizer/Moderna). Highest risk in males aged 12–24 after the second dose (roughly 1 in ~30,000–100,000 depending on age/sex/dose). Most cases are mild and resolve with treatment. Risk from actual COVID-19 infection is substantially higher (up to 40+ times in some comparisons).
- Other signals (e.g., Guillain-Barré with certain vaccines, thrombosis with viral vector types like Janssen/AstraZeneca) are rare. Updated formulations often show improved profiles.
VAERS (Vaccine Adverse Event Reporting System) logs many reports, but it is a passive system—anyone can report anything, and reports do not prove causation. Most are mild; serious events are investigated further. Large studies (e.g., 99 million people) confirm known rare risks without widespread new safety signals.
Claims of widespread “vaccine shedding” causing illness in others lack support. COVID vaccines (mRNA or viral vector) do not contain live replicating virus, so classic shedding does not occur. Infected vaccinated people can transmit the actual virus, like anyone else.
Long COVID and Other Outcomes
Vaccination generally lowers long COVID risk by reducing infection severity. Meta-analyses show vaccinated people have ~20–25% lower odds of long COVID symptoms compared to unvaccinated. Boosters provide additional benefit. Some studies show stronger effects in adolescents/children or specific eras. However, not all data are consistent, and long COVID can still occur post-breakthrough.
On excess mortality: Large studies (e.g., 30 million in France) found no increase linked to mRNA vaccines; vaccinated groups often had lower all-cause mortality. Some analyses note excess deaths in 2022–2023 coinciding with waves and other factors (aging populations, healthcare disruptions, lingering COVID effects), but vaccination campaigns correlated with reduced excess mortality in many models. Claims of vaccines driving mass excess deaths are not supported by the majority of epidemiological data.
Bottom Line: Benefits vs. Risks
- Most vaccinated people who get COVID experience milder illness than unvaccinated counterparts.
- Rare harms exist (e.g., myocarditis), but for most demographics, especially older or high-risk groups, benefits far outweigh risks. Young healthy males have the highest relative myocarditis risk but still very low absolute risk.
- Individual decisions should consider personal health, age, risk factors, and current variant prevalence. Staying up-to-date with recommended boosters helps maintain protection against severe disease
