Vaccinations, prior infection provide strongest protection against COVID

A combination of a prior COVID-19 infection together with coronavirus vaccines provides the strongest and most long-term protection against severe coronavirus disease, according to an analysis of the Finnish Institute for Health and Welfare (THL).

The newly published meta-analysis said that that the protection provided by this so-called hybrid immunity is maintained at over 95 per cent for at least 12 months, said the THL in a press release on Monday.

“It is likely that the protective effectiveness against a serious disease caused by the Omicron variant will not decrease significantly even after that time. Of course, it is worth remembering that good and long-term protection can be achieved in various ways. The recommended coronavirus vaccine doses alone provide excellent protection against developing severe coronavirus disease. The protection provided by a prior coronavirus infection is also very good and even better if combined with two vaccine doses. In other words, healthy working-age people are currently at very low risk of being hospitalised because of the virus”, said Hanna Nohynek, Chief Physician at THL.

“This further information about the protection provided by hybrid immunity and its duration is relevant to our vaccination recommendations, as the Finnish population also has antibodies that indicate a previous coronavirus infection. A large proportion of children aged 12 or over and working-aged adults have developed hybrid immunity resulting from a combination of a coronavirus infection and vaccination”, Nohynek added.

The meta-analysis is a comprehensive systematic review of 26 scientific publications examining the protection against an infection caused by the Omicron variant and severe coronavirus disease from January 2020 to June 2022.

The meta-analysis indicated that, on its own, a prior coronavirus infection provided approximately 65–70 per cent protection against an Omicron infection in the first 2–3 months, but the protection had dropped to around 25 per cent in 12 months.

Meanwhile, for those who received the vaccine and had a prior COVID-19 infection, the protection against a new Omicron infection amounted to approximately 70–80 per cent during the first three months since the most recent vaccination or coronavirus infection.

No difference was found in the protection and its duration in those who had received two or three vaccines and had a prior COVID-19 infection.

“If you have had a coronavirus infection and received two vaccines, your protection against a new infection will decrease steadily over six months. After the third dose, you will achieve short-term protection against reinfection. From the perspective of protection against the infection, even those who have had the disease will get short-term benefits from the vaccinations, but additional doses do not bring significant benefits, as protection against reinfections always decreases to a lower level after a short period of time. This would require us to keep vaccinating people again and again, which is not a smart way to use resources. New variants that evade the protection may also emerge, which could make the protection against infections lower in practice. The safety of vaccinations must also be examined alongside the benefits gained”, said Eero Poukka, Medical Specialist at THL.

A prior COVID-19 infection provides protection in the body similar to vaccination. Based on the current vaccination recommendations, this means that for those aged 18–59 and 60–64 who have no diseases that weaken the protection provided by the vaccine, a prior COVID-19 infection is considered to correspond to one vaccine dose in practice.