Market Interest Rates: Higher interest rates generally make bonds less attractive, lowering the price of FNFSSX.US, while lower rates can boost prices.

Credit Quality of Holdings: Downgrades in the credit ratings of the fund's underlying bonds can lead to price declines. Conversely, upgrades can increase value.

Inflation Expectations: Rising inflation erodes the real value of fixed-income investments, often pushing bond prices down and thus affecting FNFSSX.US negatively.

Economic Growth: Strong economic growth may lead to higher interest rates, negatively impacting bond prices in the fund. Weaker growth could support bond prices.

Fund Management Expertise: Skillful management in security selection and duration management can enhance returns and offer some protection during market volatility.

Supply and Demand Dynamics: Increased demand for the fund drives prices up, while higher supply could cause prices to fall. This depends on the fund's popularity.

Fund Expense Ratio: Higher fees and expenses can negatively impact the fund's net asset value and overall return, potentially reducing its relative attractiveness.

Maturity Profile: The average maturity of the bonds held in the fund affects sensitivity to interest rate changes; longer maturities mean more price volatility.