The second phase of the national serologic inquiry has sounded the alert to the reduction of antibodies against SARS-CoV-2 just three months after infection.
Says INSA (the national health institute Dr Ricardo Jorge) this is why people who have been previously infected need to be vaccinated.
DGS health authorities have already said that people infected naturally with the virus should sign up for vaccines using the self-scheduling platform from June.
INSA’s study involved 8,463 people, aged from very young infants to those up to the age of 79.
The document however does concede that an absence of antibodies may not mean that people are vulnerable to the virus.
“The hypothesis of antibody decay justifies the current option of vaccinating people previously infected with SARS-CoV-2, although the decay of antibodies over time – and even the absence of detectable antibodies – may not correspond to a total absence of immune memory and the maintenance of cellular immunity mechanisms”, says the document.
The ‘hedging of bets’ comes as INSA concedes that a lot more needs to be understood about the length of immunity post-infection – just as it has to be clarified how long immunity continues post-vaccination.
What does seem clear, however, is that people infected by the virus (naturally) have a lower level of antibodies present than those who have been vaccinated.
It’s not even possible from this information however to gauge ‘differences in levels of protection’.
According to INSA “whatever the case, these results support the option to vaccinate people previously infected with SARS-CoV-2”.
The preliminary results of this study were released last month, with the news that 15.5% of Portuguese were showing antibodies to the virus (click here). This will have changed markedly by now, as the vaccine roll-out has been moving swiftly through the various cohorts.
UPDATE: new text uploaded suggesting INSA’s findings may not point directly to need of people naturally infected taking up the offer of vaccination (click here)