COVID-19 variant

With older adults vaccinated, doctors say a growing share of their COVID-19 patients are in their 20s, 30s, 40s and 50s, as more contagious variants circulate among people who are still unvaccinated.

COVID-19 vaccines appear to work against the new coronavirus strains, though scientists are warily watching a variant first seen in South Africa. Vaccines may need updates to keep pace with the virus.

At least 70% of people will need to be immune from the coronavirus before COVID-19 can recede through a process known as herd immunity. Vaccines can play a role. But reaching the goal won't be easy.