The reproduction rate, or R value, of Covid-19 in India has inched up from 0.96 to 1 over the past few days and it is a matter of concern, All India Institute of Medical Sciences chief Randeep Guleria told NDTV on Saturday.

“Simply put, this means that the chances of infection spreading from a person, who has Covid, to others have gone up,” he said in an interview to the news channel.

The R value measures how many people are being infected by one Covid-positive person on an average. For instance, a value between 0.7 and 0.9 means that every 10 Covid-positive people will pass on the infection to seven to nine others.

The number of infections keeps rising if the R value is more than 1. If the value declines, the infection will eventually stop spreading because there will not be enough new cases for the outbreak to continue.

India on Saturday reported 41,831 new coronavirus cases in the previous 24 hours, taking the overall tally to 3,16,55,824 since the pandemic broke out in January last year. However, health experts believe the actual figure could be much higher.

Kerala, currently the top contributor to India’s daily new infections, has an R value of around 1.11, an analysis by the Institute of Mathematical Sciences showed. This raises the risk of an even faster spread of the virus. Meanwhile, in the North East, Tripura is the only state with an R-value much lower than one. The number in Manipur is marginally below one.

During Saturday’s interview, the AIIMS chief also mentioned a report by the United States’ Centers for Disease Control stating that the Delta variant of virus, first detected in India and now dominant across the globe, to be as contagious as chickenpox.

“Measles or chicken pox have R factor of 8 or more, which means one person could infect eight others,” the he said, explaining the CDC report. “That suggests that coronavirus is highly infectious. We saw that during the second wave in India, because entire families were getting infected. This happens with chicken pox also.”

Guleria reiterated the importance of getting vaccinated against the disease, adding that the initial eagerness among citizens to get inoculated had “waned a little bit”. He stressed that the decline in number of daily cases and reports of seroprevalence among a large section of the population should not be perceived as a reason not to get vaccinated.

“Sero surveys give you a rough idea, but they are not something that say that an area has [developed] herd immunity,” Guleria said. “...Irrespective of sero survey results, opt for vaccinations.”

Results of the fourth serological survey released by the Centre showed last month that 67.6% Indians, or more than two-thirds of the country’s population, above the age of six had antibodies against Covid-19.

State-wise data of the survey conducted by the Indian Council of Medical Research showed that Madhya Pradesh has the highest Covid-19 seroprevalence at 79%, while Kerala has the lowest at 44.4%.

Serological surveys reveal how many people may have been infected with the novel coronavirus in an area. However, it still isn’t clear how long antibodies last in infected persons and what level of antibodies is needed to protect a person from reinfection.