While Covid-19 is More Deadly and Contagious, its Vaccine is Likely to Give Long-Term Immunity

On Monday morning, district health officials in Lucknow made a frantic phone call to residents already under a two-week compulsory observation for Covid-19 post their international travel.

The caller had just one customized message for all: extend your isolation by another week as a woman in the city had tested positive 20 days after coming in close contact with a confirmed Covid-19 case.

The public health workers world over are at their wits end in combating the virus which has shown extreme virility and ability to spread at an exponential rate.

Covid-19, epidemiologist concur, is more contagious than some of the other novel-viruses which triggered health outbreaks in the last two decades.

Studies on SARS-2003 showed patients transmitted less virus at the onset of the disease. Viral shedding - defined as the period during which virus can be detected in a patient - peaked after five days and coincided with extreme clinical symptoms.

This forced patient to seek medical help followed by his complete isolation. The cycle helped in isolating an infected patient before he could transmit virus to healthy contacts.

A Covid-19 patient, on the other hand, is highly infections right from the time symptoms develop or may be a day before that.

“Even worse, one can detect a high amount of virus right before the onset of the disease. This explains why it is difficult to stop transmission by these patients”; says Dr Leo Poon of the School of Public Health Hong Kong in an online workshop with journalists earlier this week.

In fact, in the first nine days since getting exposed, a Covid-19 patient may show mild symptoms and is mobile to transmit the disease to others.

What makes the virus more contagious is its ability to survive on surfaces outside human body for a long period of time. Some tests have shown it can survive on outer surface of the mask between 4 and 7 days.

“It is difficult to control Covid-19 because patients may be transmitting from the time they are visibly symptomatic,” says Prof Malik Peiris who is credited with the isolation of SARS-2003.

The Covid-19 virus, however, is believed to be more stable than other pathogens in the category. Its mutation rate is comparatively much lower.

For the same reason, it is likely the vaccine for the disease once developed would be more effective in the long term. Flu shots are to be taken every year because the virus changes and mutates. The Covid-19 vaccine may work for longer period. But most experts believe that vaccine could take more than 12 months to develop.

“The second thing (for the likely stability of the vaccine) is that we can see the protective immunity of the virus is targeted exactly at the site at which virus binds to the cell which the virus cannot afford to mutate the site,” says Prof. Peiris.