The US must vaccinate most of the country against Covid-19 by winter to avoid more variants, expert says

With the odds stacked against the US reaching the target of 70% of adults at least partially vaccinated by July 4 — a goal set by President Joe Biden — a vaccine expert said time is running out to get ahead of the potential spread of Covid-19 variants.With the odds stacked against the US reaching the target of 70% of adults at least partially vaccinated by July 4 — a goal set by President Joe Biden — a vaccine expert said time is running out to get ahead of the potential spread of Covid-19 variants.