Routine vaccination of children in the United States appeared to have declined dramatically in March and April, in the weeks after Covid-19 was declared a pandemic and the United States government declared a national emergency, a new study published Friday shows. The authors, from the Centers for Disease Control and Prevention and other institutions, used vaccine ordering data from pediatricians who administer vaccines through the Vaccines for Children Program, which provides government-purchased vaccines to about half of the children in the United States. The study, published by the CDC in its Morbidity and Mortality Weekly Report, compared orders for the period from Jan. 7 through April 21 this year to the same period last year. The findings suggest childhood vaccination efforts nearly ground to a halt between March 13 — when the national emergency was declared — and April 19. There was a 2.5 million-dose decline in orders of regular childhood vaccines — not counting influenza vaccines — and a 250,000-dose decline in vaccines containing measles protection in that period, the authors reported.