United States manufacturing activity grew at a slower pace in April, likely constrained by shortages of inputs amid pent-up demand unleashed by rising vaccinations and massive relief packages.

The Institute for Supply Management (ISM) said on Monday its index of national factory activity fell to a reading of 60.7 last month after surging to 64.7 in March, which was the highest level since December 1983.

A reading above 50 indicates expansion in manufacturing, which accounts for 11.9% of the U.S. economy. Economists polled by Reuters had forecast the index edging up to 65 in April.

The White House’s massive $1.9 trillion pandemic relief package and the expansion of the COVID-19 vaccination program to all adult Americans has led to a boom in demand. But the pent-up demand is pushing against supply constraints as the pandemic, now in its second year, has disrupted labor supply, leading to shortages that are boosting prices of inputs.

That has been most evident in the automobile industry, where a global semiconductor chip shortage has forced cuts in production. Ford Motor Co said last week the scarcity of chips slashed production in half in its second quarter.

Technology companies are also feeling the heat. Apple warned last week that the chip shortage could dent iPads and Mac sales by several billion dollars.

Demand for goods like motor vehicles and electronics has surged during the pandemic as Americans shunned public transportation and millions worked from home and took classes remotely. Robust consumer spending helped to lift gross domestic product growth at a 6.4% annualized rate in the first quarter.

Most economists expect double-digit GDP growth this quarter, which would position the economy to achieve growth of at least 7%, which would be the fastest since 1984. The economy contracted 3.5% in 2020, its worst performance in 74 years.