This is shown by an analysis of about 500 donors from the Sanquin blood bank, who became infected with an early variant of the virus in the first months of 2020. “The main question we wanted to answer was how long immunity lasts after that early infection,” says Hans Zaaijer, medical microbiologist and principal investigator at the Sanquin blood bank. “That answer is: fairly short-lived.”
Another question was whether vaccination matters after that early infection. The answer to that is also unequivocal: yes. Without vaccination, 98 percent became reinfected, mainly due to omikron. In the group that was vaccinated after a previous infection, 62 percent experienced a reinfection before the end of 2022.
Harmless viruses
In the other 38 percent, it is only a matter of time before a reinfection occurs, says Zaaijer. “This Sars-CoV-2 virus is already starting to resemble the other four coronaviruses that are just circulating. We know from previous research that people regularly get those harmless coronaviruses. Sometimes they don’t even notice. Otherwise they will get a runny nose or a sore throat.”
However, Sars-CoV-2 is not yet an innocent coronavirus, says Zaaijer. For the elderly and people with a weakened immune system, it can remain dangerous. At the moment, about 400 Dutch corona patients are in hospital.
Milder
Sanquin’s findings were made in a relatively small group, but they are in line with other studies. A review article in the scientific journal The Lancet concludes that the early variant with which the Sanquin group became infected even protected considerably better against reinfection than later variants, such as omikron and its subvariants.
Omikron turns out milder than previous variants such as alpha or delta. But that may also be due to the immunity that has now been built up in the population, says Zaaijer. “In China, omikron has spread in recent months in a population with no appreciable immunity. By comparing mortality rates of different variants in a so-called naive population, you can conclude to what extent omikron is milder in itself. Unfortunately, the Chinese do not give those figures.”
