Residents clean the roof of their home covered in mud and ash from the nearby Taal volcano. Photo: Ted Aljibe/AFP via Getty Images
The Taal volcano eruption has turned parts of the Philippines gray with ash, as ensuing earthquakes continue and the threat of a bigger explosion remains.
What's happening: The threat level of an imminent hazardous eruption remained at 4 out of 5 Thursday, per the Philippine Institute of Volcanology and Seismology, which urged people to "guard against the effects of heavy and prolonged ashfall." The Philippine Seismic Network has recorded over 500 quakes since the first eruption Sunday.
The sought-after state of herd immunity — in which widespread outbreaks are prevented because enough people in a community are immune to a disease — is complicated by open questions about the effectiveness of a future vaccine and how COVID-19 spreads.
Why it matters: Unless a sufficient level of immunity is achieved in the population, the coronavirus could circulate indefinitely and potentially flare up as future outbreaks.