Several smaller and midsize firms such as Greenberg Glusker Fields Claman & Machtinger; Sanford Heisler Sharp; and Kline & Specter have also said more than 90% of their employees are vaccinated.

And many firms say 90% or more of their personnel are vaccinated or intend to be vaccinated by their return-to-office deadline, including Sheppard, Mullin, Richter & Hampton; Saul Ewing Arnstein & Lehr; and Ballard Spahr.

Of these firms, at least nine have mandated vaccines as a condition for returning to the office. But many of these firms have been able to achieve high figures without leaning on a mandate.

Duane Morris employment partner Jonathan Segal, who works with clients to craft vaccination policies, said that any rate "upward of 75%" is considered a good number. Herd immunity is reached when roughly 70% of a group is vaccinated or otherwise immune, experts have said, though the delta variant has created uncertainty because it can be carried by vaccinated people.

"Ninety percent is a wonderful vaccination rate," Segal said. "I think anywhere north of 75% is positive. Obviously the higher the better."

It's worth noting that the 23 firms that volunteered their vaccination rates make up just a fraction of the overall Am Law 200, which as a whole may skew lower than the firms mentioned.

Other firms are either approaching the 75% threshold, or have slightly exceeded it.

A Holland & Knight spokesperson told The American Lawyer that the firm's vaccination rate is roughly 77%, though that figure is from the firm's last study six weeks ago. Davis Wright Tremaine, which was the first Am Law 200 firm to mandate a vaccine, has about 80% of its attorneys vaccinated and 60% of its staff vaccinated.

Cozen O'Connor CEO Michael Heller said that 97% of attorneys and 80% of staff are vaccinated, a figure that is "moving up daily." Overall as a firm, Cozen O'Connor's vaccination rate is 88%.

Baker & Hostetler said it is 85% vaccinated—although the firm did not specify whether that includes the whole firm or just attorneys. Adams and Reese managing partner Gif Thornton said that, as of July 30, 90% of the firm's attorneys were vaccinated. Cleveland-based firm Thompson Hine said via a spokesperson that 75% of employees have indicated they are vaccinated. However, the spokesperson said the firm's voluntary reporting system, "necessarily involves some underreporting."

A Kobre & Kim spokesperson said the firm's vaccination rate "exceeds the local averages." McGuireWoods managing partner Tracy Walker said in an interview in late July that roughly 60% of firm personnel are vaccinated. A spokesperson for the Texas-based Winstead said the "overwhelming majority" of personnel are vaccinated.

Segal noted that a high vaccination rate isn't the end-all-be-all figure. Law firms in particular need to pay attention to ventilation in their offices, and aggregate numbers can be deceiving, especially if a company or law firm has a sprawling collection of offices. He recalls on client of his who reported a vaccination rate upward of 80% in one office while another office had just 30% of its employees vaccinated.

Even as vaccination rates increase, many law firms have opted to delay their return to office dates—with many substituting no alternative timeframe. According to a COVID-19 tracker by the New York Times, the U.S. reported 118,067 cases Tuesday—an 86% increase over the past two weeks.

Many firms are also following recent Centers for Disease Control and Prevention guidance in still requiring vaccinated employees to wear masks, regardless of vaccination status. Perkins Coie, which announced Wednesday it will require a vaccine, also noted that it is reinstituting a mask mandate in its offices.

"The CDC's July 27 guidance has necessitated a return to mask-wearing in indoor settings," a Perkins Coie spokesperson said. "Consistent with that guidance, all personnel, visitors and clients—whether vaccinated or unvaccinated—will again be required to wear masks in our offices in any common areas, including hallways, conference rooms, bathrooms or cafeterias."

Dan Packel, Dan Roe, Justin Henry, Andrew Maloney, Jessie Yount, Bruce Love and Patrick Smith contributed to this report.