WASHINGTON — Tens of millions of Social Security recipients and other retirees will get a 2.8 percent boost in benefits next year as inflation edges higher. It’s the biggest increase most retired baby boomers have gotten.Following a stretch of low inflation, the cost-of-living adjustment, or COLA, for 2019 is the highest in seven years. It amounts to $39 a month for the average retired worker, according to estimates released Thursday by the Social Security Administration.The COLA affects household budgets for about one in five Americans, including Social Security beneficiaries, disabled veterans and federal retirees. That’s about 70 million people, enough to send ripples through the economy.Unlike most private pensions, Social Security has featured inflation protection since 1975. Beneficiaries also gain from compounding since COLAs become part of their underlying benefit, the base for future cost-of-living increases.Nonetheless many retirees and their advocates say the annual adjustment is too meager and doesn’t reflect higher health care costs for older people. Federal budget hawks take the opposite view, arguing that increases should be smaller to reflect consumers’ penny-pinching responses when costs go up.