Tournaments in London, Paris, Singapore and Hong Kong were cancelled on the men's tour, while the women's circuit lost rounds in the United States, Paris and Hong Kong.
"While it is very disappointing for players, fans, organisers and everyone involved ... the health and wellbeing of the rugby community and wider society remains the number one priority," World Rugby chairman Bill Beaumont said in a statement.
"These difficult decisions have been taken following detailed consultation with our union partners and in line with advice from the various government and public health agencies around the world."
The All Blacks men's team claim a 13th title after winning three of the six rounds that were completed before the spread of Covid-19 forced the suspension of all major sport around the world.
South Africa finished 11 points back in second place with 2019 champions and Olympic gold medallists Fiji third.
The Black Ferns women's team had looked well on their way to a second successive title, and a sixth in eight years of the circuit, with four tournament triumphs in five rounds before the coronavirus shutdown.
Australia, which will defend its Olympic title in Tokyo next year, was second and Canada third.
New Zealand Rugby chief executive Mark Robinson congratulated the teams on their achievement.
"While this probably isn't the way the teams would have liked to claim the Series titles, it is a reflection of the impressive form they were in and their consistent performances throughout the season.
"It is a real credit to all players and the wider management for the work they were doing in the build up to the Tokyo Olympics, and I'm sure they will pick up where they left off when they reassemble later in the year," said Robinson.
There will be no finals for the new second-tier Challenger series this year, World Rugby said, and therefore no promotion to, or relegation from, the top tiers.
"As a result of these amendments, seedings for the Tokyo Olympic Games will be adapted to include results from the 2021 Series to ensure they provide the most robust and accurate representation of current form," World Rugby said.