Does double vaccination against influenza and COVID-19 provide additional protection against COVID-19?

The results of a study suggest that the double vaccination against influenza/COVID-19 increases protection against the severe form of COVID-19.

To remember

• Double vaccination against influenza and COVID-19 increases protection against SARS-CoV-2 infections, compared to no vaccination.

Why is this important?

• Encourage series of primary and booster vaccinations against seasonal influenza and COVID-19, highlighting the potential boost in protection against serious SARS-CoV-2 infections.

Principle results

• 21,387 adults, ages 18 and older, made up the unweighted sample selected to represent 185,251,310 adults in the United States, the weighted sample.
• Overall, 42.5% of the weighted population received both vaccines, while nearly a quarter of the population (22.4%) was unvaccinated.
• 6% of the population received the flu vaccination only; about 30% of the population received the vaccination against COVID-19 only.
• People who received both vaccines were mostly women aged 65 or older, reported good/poor health and at least 2 comorbidities.
• Double-vaccinated people had the lowest rate of SARS-CoV-2 infection (11.4%), as multivariate analysis showed that respondents who received the COVID-19 vaccination only or the double vaccination were less likely to report SARS-CoV-2 infection than unvaccinated people.
• 8.0% of people who reported SARS-CoV-2 infections were asymptomatic, about 35% to 38% had a mild to moderate form, and 19.6% had a severe form.

Methodology

• A retrospective secondary analysis investigated the association between COVID-19 and seasonal influenza double vaccination status on the one hand and the severity of SARS-CoV-2 infection/COVID-2 symptoms. 19 on the other hand, using data from the 2021 US National Health Interview Survey.
• Funding: no funding has been communicated.

Limits

• Self-report and recall bias.
• Possibility of underestimated associations between vaccination status and COVID-19 due to asymptomatic infections.