America’s booster shots have been booming. An NBC News analysis of Centers for Disease Control and Prevention data has shown that people who have received booster shots are outpacing those who had their initial doses. This is contributing to a slight increase in Covid vaccines in October.

Of the 6.7 million shots administered from Sept. 30 to Oct. 6, nearly 2.7 million were booster shots. This is compared to the almost 2 million first doses, and nearly 2,000,000 second doses during the same time period.

And of the approximately 6.4 million boosters administered in all, 4 million have gone to seniors, while the remaining 2.2 million have gone to adults from 18 to 64 years old.

In the two weeks since the Food and Drug Administration authorized a Pfizer-BioNTech booster shot for seniors and high-risk individuals, roughly 4.9 million boosters have been administered in total, according to CDC data.

The Biden administration announced the booster shot plan to most adults in August to fight the delta variant. However, the plan was cut down when it was discovered that the Moderna vaccine had not been included in the booster rollout due to the need to review its data.

Last month, a CDC advisory panel voted to approve the Pfizer boost only for seniors and people with chronic conditions. CDC Director Dr. Rochelle Walensky sidestepped that decision by adding eligibility for those at high risk of being exposed to the virus at work, including health care workers and teachers.

Additionally, many were still able to receive booster shots due to an authorization in August for those with compromised immune systems. Moderna was included in this authorization. According to CDC data, 1.4 Million people received Moderna booster shots.

Johnson & Johnson filed for booster authorization Tuesday.

Elliott Ramos is a data journalist for NBCNews.com.