It’s possible to reach herd immunity, then lose it. Here’s how to prevent that from happening.

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If you think herd immunity is the finish line to this pandemic, it’s time for a reality check.

Herd immunity with COVID-19 could come and go, scientists say. Or we might never reach it at all.

“There’s a lot of things that have to go our way to actually get to herd immunity,” said Dr. Christopher Murray, director of the University of Washington’s Institute for Health Metrics and Evaluation.

But don’t panic. Here’s why it’s possible to dip in and out of herd immunity, and what you can do now to maximize the chances of snuffing out COVID-19 for good.

In other developments:

  • President Joe Biden’s pleas for states to stick with mask mandates to slow the spread of the coronavirus were being largely ignored Tuesday as several Republican governors stayed on track to drop the requirement in their states.
  • An international team that drew up a long-awaited study of the possible origins of COVID-19 with Chinese colleagues on Tuesday called it a start, appealing for patience and noting all hypotheses — including a possible laboratory leak — cannot be fully ruled out.
  • Fearing a wave of evictions, states last year announced plans to get tens of millions of dollars into the hands of cash-strapped tenants. But nearly a year later, the efforts have had mixed results.
  • German health officials agreed Tuesday to restrict the use of AstraZeneca’s coronavirus vaccine in people under 60, amid fresh concern over unusual blood clots reported in a tiny number of those who received the shots.
  • The White House coronavirus briefings these days have a more restrained and predictable rhythm to them than the tumultuous sessions of the last administration.
  • More than 20 heads of government and global agencies called in a commentary published Tuesday for an international treaty for pandemic preparedness that they say will protect future generations in the wake of COVID-19. But there were few details to explain how such an agreement might actually compel countries to act more cooperatively.

For more summaries and full reports, select from the articles below. Scroll further for trending questions and the latest virus numbers.