CNN News:美国新冠感染人数超2800万 死亡病例突破50万

Bad news and good news related to coronavirus cases in America. First the number of deaths in which COVID-19 was cited as a factor has reached 500,000 since last winter. The number of positive tests reported in the U.S. has surpassed 28 million but that's not a record of all cases since many people who catch coronavirus have no symptoms and may not get tested.
The good news is that the number of new infections continues to drop in all but a few states. It's the first time since last fall that the average number of new cases has been less than 65,000 per day. Health officials don't know exactly why there's been such a decline. Theories include the changing seasons. Flu cases have historically decreased after February.

In some places experts believe enough people have recovered from coronavirus and developed natural immunities to it. Others say increased social distancing, mask wearing and vaccinations are having an impact though not every health official agrees with that. One thing they are warning about is that new variants or mutated versions of coronavirus could still increase its spread. Virus' mutate naturally and officials say coronavirus vaccines may not protect as well against variants.