"Control measures in Ho Chi Minh City have helped reduce the number of deaths and cut the chain of transmission," Phan Trong Lan, head of the HCMC Pasteur Institute, said Tuesday.

The effective reproduction number, known as Rt, is defined as the average number of secondary cases per primary infection cases, within a population of both susceptible and non-susceptible hosts.

The Rt number has been used to indicate how fast Covid-19 is spreading in numerous countries like Germany, the U.K. and Japan, and also by the HCMC Steering Committee for Covid-19 Prevention and Control.

Extended social distancing periods and mass testing have helped the city detect cases in several areas, including areas deemed low-risk, said Lan. That has helped with risk assessment, which would spur better measures to contain outbreaks, he added.

By allowing coronavirus cases to be isolated and treated at home, the burdens on the medical system has been reduced. Quicker transport of severe coronavirus cases between different hospitals has also helped reduce death rates. Vaccination rates in the city have also been high, Lan added.

As shown in scientific models, such coronavirus control measures between May and September have helped drive down the Rt number in HCMC from five to below 1.03, said Lan. It means around 7.4 million cases, 740,000 hospitalized cases and 55,000 deaths have been prevented thanks to the measures, he added.

As the pandemic progresses, coronavirus control measures would need to be adjusted too.

"However, if all restrictions are lifted starting Sept. 16, outbreaks would explode at a more devastating scale even compared to the current peak, and even if full vaccination rates reach 33 percent in September and 70 percent in mid-October. In such a scenario, the Rt number could hit 1.85," Lan stressed.

Restrictions need to be lifted gradually and carefully based on scientific evidence, he said, adding that relaxing restrictions starting October may slightly increase the Rt number to 1.08 before it decreases again. If restrictions are kept up until November, the Rt number may drop to below 0.91, which would sustainably reduce infection cases, he added.

Long way up

Phan Huu Phuoc, a doctor from the Medical Department of Vietnam National University in HCMC, said the Rt number can change as a population's immunity to the virus and control measures are changed. If the Rt number is larger than one, cases would increase, and vice versa. While the number of cases in HCMC remains high, there has been a marked decrease in its Rt number, he said.

"When it comes to the Delta variant, it's hard for the Rt number to be below one, no matter how many coronavirus control measures are in place and even when the population has been fully vaccinated," he said, citing Singapore, which has a current Covid-19 Rt number of 1.5, and is already considering lifting restrictions and adapting to a life with the coronavirus, while still boosting vaccination rates and protecting the most vulnerable communities from Covid-19.

While HCMC’s current Rt number is below 1.5 and its full vaccination rate only at over 20 percent, the city could still consider Covid-19 as an endemic disease and learn to co-exist with it safely once 95 percent of the population has been vaccinated with at least one shot, regular Covid-19 tests for certain populations are available, good coronavirus management measures are imposed and the economy transitions into a contactless, cashless, said Phuoc.

"The current advantage for HCMC is a Rt number lower than 1.5, so upon reopening, the economy may recover without letting outbreaks spiral out of control," said Phuoc, adding the aforementioned conditions would need to be applied in the long run until at least 80 percent of the population has been fully vaccinated, or an effective antiviral is available orally.

Therefore, the southern metropolis could reopen its economy starting October, but regular tests must be done among certain high-risk populations to detect cases quickly and readjust the Rt number, he added.

In the meantime, HCMC would need to focus on dealing with high-risk areas while keeping low-risk ones safe from the coronavirus, said Lan. A good monitoring system would be necessary to keep track of data points like infections, their severity, deaths, testing rates and others, which would help with risk assessment, he added.

"The monitoring of infection cases need to be tightly linked with quick contact tracing processes. It is one of the essential coronavirus control capabilities the WHO said to be required when it comes to Covid-19 scenarios," Lan said.

In addition, HCMC would also need to fully vaccinate everyone at risk, including the elderly and those with underlying conditions.

The southern city, epicenter of the fourth coronavirus wave, has recorded 341,699 local Covid-19 cases so far in the new wave.

It has undergone over 100 days of social distancing orders, but has now begun to shift its coronavirus fighting strategy to ease into a "new normal", including by the possible introduction of "green passes" for the vaccinated and recovered, and lifting certain coronavirus restrictions.