Updated at 12 p.m.

With slight upticks in positive testing rates linked, in some cases, to larger social events, Gov. Charlie Baker said Thursday that his administration is reviewing the state's guidance on gathering sizes, but blamed the behavior of people at some of the parties in question for the clusters of infections that have sprung up.

A large party in Chatham was linked to a cluster of new infections, and Nantucket officials are considering scaling back restaurant hours due to small increases in their infection numbers as people have been gathering on beaches close to one another without masks.

"I think that's one of the things we're talking about," Baker said at a press conference when asked about the state's gathering size limits. "But the bigger issue is not so much the nature of the size of some of these gatherings, especially the private ones that are going on in backyards and place like that. The bigger issue is honestly the behavior generally at those, which is not socially distant, no masks and in some respects a lack of respect for how this virus works and how it moves form person to person."

The state's guidance instructs people to limit indoor gatherings to 25 people, and a maximum of 100 people outdoors depending on the size of the venue. The state's positive test rate is at 2 percent currently, which is still low, but has been ticking up slightly over the past week or so.

"To all our residents I can't express this enough. Don't be careless or complacent," Baker said.

Baker was at Pfizer's facilities in Andover where the pharmaceutical giant is entering third-phase clinical trials for a vaccine for COVID-19 that is expected to involved up to 30,000 test patients. Pfizer is one of several Massachusetts companies chasing a vaccine, and officials hope to be able to file for regulatory approvals for emergency use by October.

The company said it expects to produce 100 million doses of the vaccine by the end of the year, and have the capability to make 1.3 billion doses by the end of 2021. It's mRNA vaccine requires two doses per patient.

"Until we have a treatment or a vaccine, and I know you're working on that one, we have to learn how to continue to live with this virus," Baker said.