BOSTON (CBS) — The Delta variant now accounts for 1 in 4 COVID infections in the United States and concerns have prompted Los Angeles health officials to recommend indoor mask use for everyone, including those who are vaccinated.

So if the vaccines are working against the variants, why the need to mask up again?

READ MORE: CDC Expected To Recommend Face Masks For Fully Vaccinated Americans Again In Some Indoor Settings

In large part it’s because this particular variant spreads so easily. Studies have shown that the vaccines provide good protection against serious illness caused by the variants, including the delta variant.

But there are reports of people who are fully vaccinated still getting infected and it’s still not clear if they can then easily transmit this highly-contagious variant on to others who are vulnerable. So while the CDC broadly says that vaccinated people do not have to wear masks, it is leaving it up to local officials to determine whether masks should be worn in areas with low vaccination rates or rising cases.

READ MORE: Crash Caught On Camera Amid Uptick In Complaints About Off-Road Vehicles In Pelham, NH

As for Massachusetts, we have a high vaccination rate here and cases continue to fall, so I don’t think it’s necessary right now, but I will always advise you to err on the side of caution.

So if you’re vaccinated but you’re more comfortable wearing a mask, then by all means do so. Not because you’re likely to get sick from COVID-19 but because you could inadvertently pass this delta variant on to someone who is not protected.

MORE NEWS: Mass. Traffic Is Back To Pre-Pandemic Levels, But At Different Times And Routes

There are situations in which I feel more comfortable wearing a mask, like when I’m tightly packed with others indoors or near unvaccinated children.

Dr. Mallika Marshall