Protection against COVID-19 after vaccination, previous infection

Editor's Note

This study from the UK finds that two doses of the Pfizer-BioNTech vaccine were associated with high short-term protection, but this protection waned considerably after 6 months; whereas, infection-acquired immunity boosted with vaccination remained high more than 1 year after COVID-19 infection.

Of 35,768 participants analyzed, 9,488 (27%) had a previous COVID-19 infection, and 95% had received two vaccine doses of Pfizer-BioNTech or AstraZeneca vaccines.

Between December 7, 2020, and September 21, 2021, there were 2,747 primary infections and 210 reinfections.

Among previously uninfected participants who received Pfizer-BioNTech vaccinations with a long interval between doses, vaccine effectiveness fell from 85% at 14 to 73 days after the second dose to 51% at a median of 201 days. Effectiveness was similar in those who received vaccinations with a short interval between doses.

Among those who received AstraZeneca vaccinations, vaccine effectiveness dropped to 58% at 14 to 73 days after the second dose.

Infection-acquired immunity waned after 1 year in unvaccinated participants but remained high in 90% of those who were subsequently vaccinated, even in those infected more than 18 months previously.

The researchers concluded that the highest and most durable protection was seen in those who received one or two doses of the Pfizer-BioNTech vaccine after being infected with COVID-19.