Soon after their arrival in late December 2020, Covid-19 vaccines turned the pandemic around and paved the way for a return to normality. According to one estimate, they have prevented around 14.4 million deaths worldwide.
In a small percentage of people they also produced side effects.
Over the course of more than a year, The New York Times spoke to 30 people who said they had been harmed by Covid vaccines. Their symptoms may turn out to be unrelated to the injections. But they — along with more than a dozen experts — believe federal officials aren't doing enough to investigate their complaints.
All vaccines carry some risk of side effects. More than 270 million Americans have received about 677 million doses of Covid vaccines, and even rare side effects — occurring in, say, only 0.001% of patients — could mean thousands of recipients have been affected.
In fact, more than 13,000 have submitted claims to a government fund that compensates people for injuries caused by the Covid vaccine. So far, however, only a dozen people have been compensated, almost all for heart problems caused by vaccines.
Here are four highlights from our investigation.
For most people, the benefits of Covid vaccines outweigh any risks.
Even the best vaccines and medications have some side effects. This does not negate their benefits, nor does it suggest that people should stop taking them.
The rotavirus vaccine, for example, is an unqualified success, but it can lead to intussusception – a life-threatening condition in which the intestine folds in on itself – in about 0.02% of vaccinated children.
Some side effects caused by Covid vaccines may be equally rare. Researchers in Hong Kong analyzed health data from that country and found that about seven in a million doses of the Pfizer-BioNTech vaccine triggered a shingles attack severe enough to require hospitalization.
Other side effects are slightly more common. Covid vaccines can lead to myocarditis, or inflammation of the heart, in one in 10,000 adolescent males. (Myocarditis is one of four serious side effects recognized by federal health officials.)
Deaths caused by vaccines are extremely rare, despite claims by some conspiracy theorists that vaccines have led to a spike in death rates.
Deeper analysis may indicate that in some groups, such as young people, the benefits of Covid shots may not outweigh the risks. But for most Americans, vaccines continue to be much safer than contracting Covid itself.
Federal surveillance has found some side effects but may miss others.
To detect problems with vaccines, federal agencies rely on multiple databases. The largest, the Vaccine Adverse Event Reporting System, is useful for generating hypotheses, but contains unverified reports of harm. Other databases combine electronic health records and insurance claims.
These systems have identified blood clotting problems associated with the Johnson & Johnson vaccine and a potential risk of stroke after immunizations with mRNA, which is still being studied. But federal researchers followed Israeli scientists in identifying myocarditis as a problem among young people.
The American healthcare system is fragmented, with medical records stored by multiple companies that don't collaborate. Electronic health records do not describe all symptoms the same way, making comparisons difficult. Insurance claims databases may not contain records of shots administered at mass vaccination sites.
Federal systems may also miss symptoms that defy easy description or diagnosis.
Proving that vaccination led to a disease is complicated.
Among the hundreds of millions of Americans immunized against Covid there have been deaths, heart attacks, strokes, miscarriages and autoimmune diseases. How to distinguish diseases caused by the vaccine from those that would have occurred anyway?
The rarer the condition, the more difficult it is to answer this question.
Judging simply by timing – that is, the appearance of a particular problem after vaccination – can be misleading. Most famously, childhood vaccines were mistakenly linked to autism because the first noticeable characteristics often coincided with the immunization schedule.
Serious side effects may appear for the first time in animal vaccine studies. But few such studies were possible given the nation's desperate timing in 2020. Clinical trials of the vaccines were intended to test their effectiveness, but were far from large enough to detect side effects that may occur in only a few people per million doses.
Most independent studies of side effects have not been large enough to detect rare events, nor to rule out their possibility; others searched only for a preset list of symptoms and may have missed rare outliers.
An expert panel convened by the National Academies concluded in April that, for most side effects, there was insufficient data to accept or reject a link to Covid vaccination.
Understanding the full range of side effects can take years.
Federal health officials recognize four major side effects of Covid vaccines, not including temporary pain at the injection site, fever and malaise that can accompany the shots.
But in federal databases, thousands of Americans have reported that Covid vaccines have caused ringing in the ears, dizziness, brain fog, sharp fluctuations in blood pressure and heart rate, new or recurring autoimmune conditions, hives, vision problems, kidney problems, tingling, numbness. and a loss of motor skills.
Some studies looked at reports of side effects and largely concluded that there was no link. Closer examination may reveal that many, perhaps most, of the other reported side effects are unrelated to immunization. Most of them are also associated with Covid and could be the result of undiagnosed infections. But without extensive studies it's impossible to be sure, experts say.