The group, which included a seven-year-old boy, was picked up when the vehicle travelled through a checkpoint in the southerly coastal province of Binh Thuan, local media reported.
Vietnam’s government has imposed strict lockdown restrictions which bar people travelling from their homes in many areas across the country as the nation battles the latest wave of the pandemic.
According to reports in local Vietnamese newspapers, the group had travelled dozens of miles inside the sealed refrigerated truck from southern Dong Nai province, an industrial area that has recorded more than 35,000 Covid-19 cases and 320 deaths.
That province has been in total lockdown since July with the virus surging to such an extent that makeshift field hospitals have been constructed to care for those infected.
"We knew it is a huge risk and very dangerous to stay in a closed frozen truck, but we faced a higher risk if we were infected with the virus," one of the Covid refugees, who was with his seven-year-old son, told a Ho Chi Minh City news website.
The lorry was pulled over at a checkpoint which was enforcing the lockdown restrictions after the vehicle aroused the suspicion of police officers.
"Police were so surprised to see 15 people at the back of the truck... Some of them were sweating and showed symptoms of breath shortness," the report added, stating the passengers were also carrying negative Covid test certificates.
The passengers reportedly had asked the driver to turn off the refrigeration in the back of his vehicle because it had got too cold. They told the police they were attempting to flee the badly-hit Dong Nai region and get back to their homes in central Vietnam.
After being praised for its initial handling of the pandemic and effectively crushing daily cases and deaths to zero throughout 2020, in recent months Vietnam has suffered a sudden spike.
Since the latest wave began in July, daily deaths have been averaging more than 300 a day. All road and air links from the south of the country, which has been the epicentre of the surge, have been shut down as the authorities attempt to bring the outbreak under control.
Only 5.2% of its 98 million people living in Vietnam have been vaccinated.
Ho Chi Minh City – the centre of the Covid surge – has extended its local lockdown restrictions even as the capital Hanoi and other provinces have begun to ease the curbs and domestic flights will shortly resume.
The city of nine million said extending its own lockdown for the rest of the month was necessary to continue isolating outbreaks and prevent its health services from being overwhelmed.