COVID-19 summer surge his the Bay Area again

The annual summer surge of COVID-19 infections has begun in San Francisco.

Why it matters: In addition to the spread of new variants, people congregating indoors to avoid extreme heat and an extremely busy July 4 travel period are expected to drive up infections.

Threat level: While experts expect this summer wave to remain mild, it's a reminder to remain vigilant, particularly among those who are medically vulnerable.

By the numbers: Cases are growing or likely growing in 39 states, according to the latest CDC data — including California, which has seen a surge in the levels of COVID discovered in human sewage.

• Hospitalizations and deaths remain low.
• The KP.3 and KP.2 strains, descendants of the highly contagious JN.1 variant and among the so-called FLiRT variants , account for more than half of infections, according to the CDC .

Zoom in: San Francisco's 7-day average test positivity rate , which dropped from nearly 9% to around 1% in April, has steadily increased in recent weeks and now sits at over 5%.

• Wastewater surveillance in the city also reflects that surge.

What to watch: The CDC recommended last week that everyone ages 6 months and older get an updated COVID vaccine , regardless of whether they've been vaccinated before.

• The FDA has recommended that drugmakers target the KP.2 strain .