Between February 15-21, such homes counted just 215 Covid-19 infections compared with 4,439 cases between January 18-24, representing a 95 percent drop, said the Institute for the Elderly and Social Services (Imserso) in a report published late Tuesday.
The number of deaths also fell from 673 to 157 — representing a 77 percent drop.
Spain began its vaccination drive on December 27 at care homes, and by mid-January residents and staff started getting their second jab.
The report also said 29,408 nursing home residents had died from the virus since the start of the pandemic in the first-ever estimate by a government agency of the overall toll.
The figure includes confirmed cases as well as deaths from suspected cases of the virus.
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Spain has so far recorded nearly 70,000 deaths since the pandemic began and more than 3.1 million cases.
Some regional governments, which are responsible for health care, have provided a figure for care home deaths but the national government has still not given a national number.
In early December, another government agency estimated that between 47 and 50 percent of deaths in the first wave of the pandemic occurred in elderly care homes.
Amnesty International has said the “vast majority” of seniors in Spanish retirement homes were not properly cared for in the first weeks of the pandemic.
Troops brought in to fight the outbreak found elderly people abandoned in care homes and in some extreme cases dead in their beds, with bereaved family members launching legal action against a string of residences.
Over 1.2 million people have been vaccinated in Spain since the start of its immunisation campaign.
The government aims to have 70 percent of Spain’s population of around 47 million vaccinated by the end of August.