Natural immunity in Portugal

Rise of natural acquired immunityShow more

Risk of BA.5 Infection among Persons Exposed to Previous SARS-CoV-2 Variants

https://www.nejm.org/doi/full/10.1056/NEJMc2209479?query=TOC&cid=NEJM%20eToc,%20September%201,%202022%20DM1402792_NEJM_Non_Subscriber&bid=1141953912

https://www.nejm.org/doi/suppl/10.1056/NEJMc2209479/suppl_file/nejmc2209479_appendix.pdf

Omicron subvariants, BA.1 and BA.2, displaced by BA.5 in many countries

Greater transmissibility

Partial evasion of BA.1- and BA.2-induced immunity

Portugal, one of the first countries affected by a BA.5 predominance

N = 9,307,996

All Portuguese residents aged 12 years and older, (National Census 2021)

Uninfected people in June 1st 2022 was 5, 328, 287, (57% of the Portuguese population over 12)

(PCR tests and rapid antigen tests to diagnose cases)

Presence of undocumented infections among the “uninfected” group of individuals

29.2% of infections were not notified

(based on the seroprevalence of SARS-CoV-2 anti-N IgG in the population)

National coronavirus disease 2019 registry (SINAVE)

(all reported cases in the country, regardless of clinical presentation)

To calculate the risk of BA.5 infection after documented infection with past variants,

including BA.1 and BA.2

Times when different variants represented more than 90% of the isolates

To calculate their infection risk during the period of BA.5 dominance

Pooled BA.1 and BA.2 (slow transition between the two subvariants)

Comparator group

Population that did not have any documented infection before BA.5 dominance (June 1, 2022)

Results

Wuhan-Hu-1 55.7%

Alpha 58.8%

Delta 64.5%

BA.1 / BA.2 7 76.8%

We found that previous SARS-CoV-2 infection had a protective effect against BA.5 infection

Protection was maximal for previous infection with BA.1 or BA.2 (not surprising)

Context

Portugal more than 98% of the study population completed the primary vaccination series before 2022

There is a perception that the protection afforded by previous BA.1 or BA.2 infection is very low, given the high number of BA.5 infections among persons with previous BA.1 or BA.2 infection.

Our data indicate that this perception is probably a consequence of the larger pool of persons with BA.1 or BA.2 infection than with infection by other subvariants, and it is not supported by the data.

Breakthrough infections with the BA.5 subvariant were less likely among persons with a previous SARS-CoV-2 infection history … especially for previous BA.1 or BA.2 infection, than among uninfected persons.