COVID-19 reinfections are likely much worse than we know

In October, Victorian Premier Daniel Andrews announced that a Melbourne resident who tested positive in July had tested positive again.

An expert panel had reviewed the case and concluded there was not enough evidence to say his positive test presented viral shedding from the original infection.

This is where the boundaries get fuzzy because people with the virus can continue to test positive for several months without being sick or infectious.

The register only confirms a reinfection when testing shows the genetic makeup of each viral infection is different to a degree which cannot be explained through natural evolution.

Today, a spokeswoman from Victoria’s Department of Health and Human Services said this case was managed and classified as possible reinfection to ensure there was no possibility of community transmission.

It was not possible to use genomic data to reach a firm conclusion and she said there had been no onward transmission from the case.

Second reinfection death

The latest case to land on the A register is from Israel where a man became the second person, worldwide, to die from a confirmed case of reinfection.

Aged 74, he became ill with COVID-19 in August, recovered and had three follow-up negative tests. Then he fell ill a second time and died in late November.

The first death was a woman, 89, from the Netherlands, who was undergoing chemotherapy. There have been 24 deaths on the B register.

So far, the tracker shows the average interval between confirmed infections is 80 days.

“The numbers of reported reinfections are clearly an underestimation," says Professor Ivo Mueller, joint head of population health and immunity at the Walter and Eliza Hall Institute of Medical Research (WEHI).

“Confirming reinfection requires sequencing to determine the two infections have a different viral genome and for most suspected cases, that data is not available.

“In areas with very little transmission, like Australia, where we sequence all viruses, reinfection is very uncommon. The case number is low so the probability of someone getting exposed twice is minuscule.

“In other areas where the numbers are very high, like the US or the UK, only a very small proportion of the viruses actually get sequenced. So, very often, of the two potential infections, the sequence may not be available for the first. It is then not possible to confirm if the second was a recurrence or a new infection.”

He says in areas of high transmission many reinfections may go undetected because they are asymptomatic. They may only be detected as part of contact tracing which, unlike in Australia, is less complete in many countries abroad, simply because they can’t keep up.

Reinfection occurs when a person’s immune system is no longer able to completely suppress the virus. Professor Mueller says it is not known how long the period of complete suppression following natural infection with this virus will last.

“We expect there is a first phase where there is a complete suppression. There may be a period after that, where reinfection is possible but people do not get sick.

“Whether they may transmit the virus is not yet clear. Then there will be a period of a couple of years, where immunity may be completely lost.”

He is working on a study at WEHI trying to understand the timing of these stages of immunity and says the same understanding is needed for immunity conferred by vaccines.