The COVID-19 pandemic has sent home prices soaring across Massachusetts as demand exploded, inventory shrank and time-on-market dropped below one month in many markets.

But a new study by First American has found that Greater Boston’s price jumps in October were the third worst in the nation on a year-over-year basis.

The median single-family home sale price in October jumped between 12 and 17 percent across the five counties that traditionally make up Greater Boston – Essex, Middlesex, Norfolk, Plymouth and Suffolk – according to The Warren Group, publisher of Banker & Tradesman, with Norfolk (15 percent), Middlesex (16 percent) and Plymouth (17 percent) counties seeing the biggest surges.

Price increases in the condominium market that month were more uneven across the metro, according to The Warren Group: 1 percent in Suffolk County, 4 percent in Essex County, 9 percent in Middlesex County, 18 percent in Plymouth County and 23 percent in Norfolk County.

First American said its Real House Price Index dropped 11.6 percent for Greater Boston, putting it just behind tech hub San Jose, California (13.6 percent decline) and its infamously unaffordable neighbor to the north, San Francisco (16.9 percent drop).

The index measures the price changes of single-family properties throughout the U.S. adjusted for the impact of income and interest rate changes on consumer house-buying power over time at national, state and metropolitan area levels. Because the index adjusts for house-buying power, it also serves as a measure of housing affordability.

The October median single-family sale price sat at $520,000 in Essex County, $$620,550 in Middlesex County, $570,000 in Norfolk County, $449,500 in Plymouth County and $642,500 in Suffolk County, The Warren Group reported. The October median condo sale price was $350,000 in Essex County, $475,000 in Middlesex County, $480,000 in Norfolk County, $375,000 in Plymouth County and $610,000 in Suffolk County.

“Mortgage rates are fairly consistent across the country, so when mortgage rates fall, they boost house-buying power and increase affordability in every city. However, the other components of the RHPI, household income levels and nominal house prices, vary market by market, so they do not have a uniform impact on affordability. During the initial months of the recession, from March through June, affordability improved because falling rates and rising incomes were enough to offset house price appreciation gains,” First American Chief Economist Mark Fleming said in a statement. “However, as potential homebuyers emerged from the stay-at-home orders implemented early in the pandemic, the housing market began to heat up once more. Comparing the RHPI levels in October relative to the resurgence of home buyer interest in June, affordability declined in 24 of the top 50 markets we track.”

Massachusetts as a whole came in fourth in First American’s rankings of states with worsening affordability year-over-year. The Real House Price Index for the state dropped 7.6 percent, tying it for second-worst drop with New Hampshire, whose southeastern quarter is closely tied to the Greater Boston economy, and geographically constrained Hawaii. California saw the worst decrease in affordability in First American’s data, with its Real House Price Index falling 9 percent.

“The [national] housing market prior to the pandemic could have been characterized as a sellers’ market, with a shortage of supply relative to demand. With the current supply of homes for sale even tighter relative to demand, it can only be characterized as a super-sellers’ market today. The pandemic has intensified a sense of home as refuge and falling mortgage rates have made financing a home purchase historically inexpensive,” Flemming said. “As a result, demand for homes has surged while the supply of homes for sale has fallen to near record lows, resulting in rapid house price appreciation. Nominal house price appreciation was 7.9 percent higher in October than in March of this year, a precipitous rise in just seven months that has pushed back against the 10.7 percent increase in house-buying power over the same period.”

Not all communities saw decreases in their affordability on a year-over-year basis. Cleveland and Pittsburgh both saw their Real House Price Index figures grow by 4.8 percent and 4 percent respectively, with Kansas City, Missouri (2 percent growth), New Orleans (1.8 percent growth) and Nashville, Tennessee (0.8 percent growth) rounding out the top five.

“In 2021, mortgage rates are anticipated to remain near historic lows and the economy should improve as vaccinations become more widespread. Both of these conditions will keep house-buying power strong in 2021,” Fleming said. “Yet, housing supply constraints will likely remain and continue to fuel a sellers’ market. The question is, will robust house-buying power be enough to offset strong nominal house price appreciation, or will the trend of declining affordability continue?”