| Just about all of us have had multiple bouts of cold and flu. But what about Covid-19? Sometimes, as in colds, an illness isn't serious enough for the body to develop a "memory" that helps raise immune defenses the next time they're challenged. In the case of flu, the immune system often fails to repel repeat infections because the virus constantly evolves to avoid recognition, which is why new vaccines are needed annually. Like some common colds, Covid-19 is caused by a coronavirus, so perhaps it shouldn't be surprising that some reinfections have been reported. Yet it's troubling because the virus is so dangerous, especially in older people and those with health conditions such as obesity or diabetes. Reinfections currently appear to be very rare – just five out of more than 41 million Covid-19 cases reported worldwide. But they may be seen more frequently as time goes on. This could happen if the virus begins mutating, but that seems unlikely because its genome is known to have a self-correcting mechanism that minimizes changes.  Still, it's possible that our immune systems won't consistently mount a strong or durable reaction to the virus. And we know that the pathogen is very good at evading the human immune system through multiple mechanisms. So avoiding reinfections will likely depend on arrival of an effective vaccine. Most of those in development target the spike protein, a part of the virus that has shown little change over time. And some types of shots could be quickly adapted to fight new, mutated versions of the virus if they occur. The vaccines don't have to work perfectly in the most susceptible people such as the elderly, because a good campaign in younger individuals will create the "herd immunity" that we all keep hearing about. If they work poorly or not at all, we'll be in a tough spot. But I remain optimistic that we'll get one or more vaccines that can help us manage this disease, including reinfections. That's why I say don't worry … just yet. – Sam Fazeli | 
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