Cambridge continues to offer free Covid testing by appointment in Kendall Square. (Photo: Marc Levy)

Covid-19 testing has dropped sharply in Cambridge even as a new, more contagious form of the virus becomes more prevalent, especially in New England. Next month the city will cut its walk-in testing program from two days to one day a week after offering free tests as often as five days weekly earlier in the pandemic. And the Massachusetts Institute of Technology has eliminated mandatory testing for students and staff.

Yet despite optional testing at MIT, cases have begun rising there after initially falling. And infections among Cambridge residents are seesawing after plunging quickly from the omicron peak in early January. The weekly average case rate in Cambridge on Friday was higher than at any other point in the pandemic except during the surge caused by the highly contagious omicron variant.

Cambridge is still offering free testing – only by appointment – seven days a week in partnership with the private company CIC Health in Kendall Square.

At MIT, new weekly cases fell to 82 from 142 after mandatory testing for students ended March 14, according to the school’s Covid-19 dashboard. (The weekly periods were March 6-12 and March 13-19).

Asked how MIT knew that fewer tests had not led to lower case counts, spokesperson Sarah McDonnell said Tuesday: “Positive test numbers at MIT have been dropping steadily since January, so at this point we expect to see fewer cases from week to week regardless of our testing requirements.”

Within a few days of that pattern, though, weekly case numbers began rising at MIT, and they have continued to climb. At Harvard University, a surge among undergraduates led officials to require undergrads to test more often starting in early March. New cases are down among undergraduates, but on March 21 total infections at Harvard spiked at 106, with 65 graduate students testing positive.

McDonnell said MIT is urging students and staff members – employees’ testing mandate ended on Feb. 21 – to get tested if they have Covid-19 symptoms, have been exposed to the virus or think they face increased risk. Whatever their situation, anyone can get tested on demand, she said. “We continue to monitor the data, and remain prepared to adjust our policies as needed to address any kind of surge or issue we notice in our positive cases,” McDonnell said.

MIT is no longer publishing one measure of testing adequacy, though: the percentage of tests that are positive. Earlier in the pandemic, experts said high test positivity could indicate that more testing was needed because it meant that only people with heightened symptoms were being tested, while many people who could spread Covid had mild or no signs of illness.

The school stopped disclosing the percentage of positive tests when it made testing optional because “displaying percentage-based positives would provide an incomplete view of Covid-19 rates on campus, because those choosing to test are more likely to be positive and because fewer community members are testing,” its Covid-19 dashboard says.

Testing in Cambridge fell steeply in the two weeks before March 19, according to the most recent report by the state Department of Public Health. The department publishes two-week testing figures for cities and towns every Thursday.

There were 40,098 Covid-19 PCR tests performed in the city between March 6-19, according to the report from Thursday. That compared with two-week test figures ranging from more than 56,000 to more than 60,000 in three previous Thursday reports. The city still has one of the highest testing rates in Massachusetts.

The state figures include all tests performed within Cambridge, not just those provided by the city. An update from the city on Friday said officials cut back walk-in tests because of lower demand and the continued option of appointment-only tests at CIC.

The average number of new cases has wavered but remains relatively high. City health officials say they are keeping an eye on the new omicron subvariant called BA.2, which has caused surges in Britain, Hong Kong and some European countries. The most recent estimate from the Centers for Disease Control and Prevention puts BA.2 at about 55 percent of cases in New England. Scientists say it is more contagious than omicron, which caused record-breaking numbers of new infections in Cambridge in December and January.