More than 17,800 people in Puerto Rico have received the COVID-19 vaccine since the first dose was administered earlier this week, with the U.S. territory expecting tens of thousands of additional vaccines to arrive in upcoming weeks, officials said Friday.

Dr. Iris Cardona, sub-secretary of Puerto Rico’s Health Department, said some 21,400 Pfizer vaccines will be delivered weekly for the next four to six weeks. If the Moderna vaccine is approved, she said the island will receive the first 47,500 doses next week of a total of 60,400 requested.

So far, officials have delivered nearly 30,000 Pfizer vaccine doses to hospitals across the island this week, with only a couple of hundred doses withheld because they didn’t come with the solution required to dilute them. Cardona said the problem resulted from a distribution chain error. She also blamed miscommunication for 13 of 65 hospitals not receiving the doses on Tuesday as scheduled, saying that some filled out an application stating they didn’t have the proper equipment to store the doses at sub-zero temperatures when in fact they did have it.

The government has said it hopes to vaccinate 70% of Puerto Rico’s 3.2 million inhabitants by August at the latest.

First in line to be vaccinated are health workers, emergency responders, hospital employees and those who live or work in shelters or nursing homes. Next will be police officers, employees of the island’s Department of Education and other workers considered essential, followed by people with compromised immune systems, cardiac problems or chronic health conditions including diabetes.

Given that Puerto Rico is an island, many worry that the delivery of the second required Pfizer vaccine dose could be delayed. Cardona addressed those concerns, saying there’s no problem in administering the second dose later than the recommended date. Officials added that if there’s a significant delay in the arrival of the second dose, they’ll withhold vaccinations of the first dose until the others arrive.

Puerto Rico has reported more than 112,000 confirmed and probable cases and more than 1,300 deaths.