MEXICO CITY — Mexico began vaccinating senior citizens in more than 300 municipalities across the country Monday after receiving some 870,000 doses of the AstraZeneca COVID-19 vaccine.

Most of the effort was concentrated in remote rural communities, but in a few far-flung corners of the sprawling capital, hundreds of Mexicans over the age of 60 lined up before dawn for the chance to get vaccinated.

The government has designated 1,000 vaccination sites, including schools and health centers, mostly in the country’s poorest communities.

President Andrés Manuel López Obrador conceded Monday that bad weather and snow had kept the vaccine from arriving to some isolated areas in Mexico’s northwest. He said the armed forces, which are in charge of logistics for the vaccination campaign, were working to access those areas.

Mexico started vaccinating health workers in mid-December with 726,000 doses of the Pfizer vaccine.