TOKYO, July 21 (Reuters) - Japanese stocks rose on Tuesday as signs of progress in developing a COVID-19 vaccine boosted investor confidence about a recovery in the global economy.

The Nikkei index ended up 0.73% at 22,884.22, with the healthcare and technology sectors leading the advance.

Initial findings from trials of three potential COVID-19 vaccines have shown encouraging results, raising hopes for a medical solution to a global pandemic that has triggered a sharp recession and caused more than half a million deaths.

"This is certainly a positive development for stocks, but the upside is limited because we still don't know how long it will take for a vaccine to be completed or how it will be distributed," said Kiyoshi Ishigane, chief fund manager at Mitsubishi UFJ Kokusai Asset Management Co.

"At this point, it's better to buy on dips instead of aggressively chasing the upside."

There were 72 advancers on the Nikkei index against 148 decliners.

The largest percentage gainers in the index were pharmaceutical firm Daiichi Sankyo Co Ltd, up 5.63%, followed by Z Internet services firm Holdings Corp, gaining 5.39%, and silicon wafer maker Sumco Corp, up by 4.24%.

The largest percentage losers in the index were Taiheiyo Cement Corp, down 4.01%, followed by Nippon Steel Corp , losing 3.33%, and auto maker Isuzu Motors Ltd , down by 3.13%.

Shares of mobile phone network operators NTT Docomo Inc , KDDI Corp, and Softbank Corp dropped following a report that the Japanese government was considering preventing wireless carriers from charging customers fees when they switch providers.

The broader Topix rose 0.36% to 1,582.74.

The volume of shares traded on the Tokyo Stock Exchange's main board was 1.15 billion, compared with the average of 1.25 billion in the past 30 days. (Editing by Sherry Jacob-Phillips and Subhranshu Sahu)