The immune system has two main arms, and the first kicks in as soon as the body detects a foreign intruder. White blood cells swarm to the site, prompting inflammation that's responsible for chills, soreness, fatigue and other side effects.

The latest guidance from the U.S. Centers for Disease Control and Prevention says you don't need to be tested or to quarantine if you're fully vaccinated, even if you've been exposed to someone who was sick — but there is an exception.

One doctor says "waves and waves" of "long-haul" covid patients remain sick long after retesting negative for the virus. A significant percentage are suffering from syndromes that few doctors understand or treat.

Production of another potential vaccine against COVID-19 will begin within weeks, its developers Sanofi and GlaxoSmithKline said Thursday as they launched a large trial enrolling 35,000 adult volunteers in the United States, Asia, Africa and Latin America

Keen to avoid losing another summer of holiday revenue to the coronavirus pandemic, the European Union, some Asian governments and the airline industry are scrambling to develop so-called COVID-19 vaccine passports to help kickstart international travel.

Experts worry that blind spots in the power of a federal warning system for vaccine safety issues, could hamper detection of other unexpected side effects.

While the symptoms show your immune system is responding to the vaccine in a way that will protect against disease, evidence from clinical trials showed that people with few or no symptoms were also protected. Don't feel bad if you don't feel bad.

A new study in Nature found alarmingly high rates of opioid use among covid survivors with lingering symptoms at Veterans Health Administration facilities.

Just as other industries are rolling back some consumer-friendly changes made early in the pandemic — think empty middle seats on airplanes — so, too, are health insurers.

"We only have information for as long as the vaccines have been studied," said Deborah Fuller, a vaccine researcher at the University of Washington.