Unvaxxed could get Covid every 16 months

Relying on herd immunity without widespread vaccination jeopardises millions of lives, entailing high rates of re-infection, morbidity, and death. Yale School of Public Health

study

Unvaccinated individuals could expect to get re-infected with Covid-19 roughly every 16 months due to waning immunity, a study has found.

Yale School of Public Health analysed data for coronaviruses similar to Covid-19 including Sars-CoV-1 and Middle East respiratory syndrome (Mers-CoV), to estimate the likely re-infection rate for Covid-19.

Despite mounting reports of reinfection for Covid-19, the numbers are still not high enough for a Covid study, so scientists analysed data from similar diseases. The research published in the Lancet Microbe estimated immunity in those who got Covid-19 weakened fairly quickly.

Yale research associate Hayley Hassler, one of the study’s co-authors, said the risk of re-infection was about 5 per cent at three months after infection, and 50 per cent after 17 months. People could get re-infected anywhere between three months to five years — with a median of 16 months.

The figures assume that Covid is circulating in the community and restrictions such as masks and social distancing are not observed.

The study also noted immunity could vary significantly among individuals, this could depend for example, on whether the person was asymptomatic, which could produce a weaker immune response than if they did get symptoms.

“Individuals may experience longer or shorter durations of immunity depending on immune status, cross-immunity, age and multiple other factors,” Hassler said.

As the pandemic continues, scientists believe re-infection is likely to become increasingly common. The study notes that maintaining social distancing measures, even for those who have already been infected, and speeding up vaccinations would be critical to preventing deaths.

“We need to be very aware of the fact that this disease is likely to be circulating over the long term and that we don’t have this long term immunity that many people seem to be hoping to rely on in order to protect them from disease,” Yale professor of biostatistics and the study’s lead author, Jeffrey Townsend, said.

The findings are also significant for reaching herd immunity. The study “argues strongly” against trying to achieve this without vaccination.

“Relying on herd immunity without widespread vaccination jeopardises millions of lives, entailing high rates of re-infection, morbidity, and death,” the study stated.