How long should you wait for a booster COVID-19 vaccine? Is it wise to get the flu vaccine and COVID booster at the same time?

These are the most common questions I received this these days, and the answers are finally becoming clear.

Many individuals have been infected with Omicron in the last nine months and therefore have an immunity boost from their infection. In fact, data now indicates that hybrid immunity generated this way is stronger than vaccines alone in preventing new infections (although the vaccines alone are still highly effective in preventing severe disease). A new article estimates that infection with Omicron is almost 80% effective in preventing new infection with the most recent strains (BA4, BA5) that the new boosters were designed to prevent.

The government will not give you a booster unless you’re two months out from an infection or prior shot. I feel that this is too short a time period in which to get a booster because the immunity from the prior infection or vaccine will neutralize the new shot before it can boost immunity. I have been telling people to wait at least four to six months for a booster shot. 

There is now better data to support my position.

Earlier work has shown that waiting longer for a second dose of COVID mRNA vaccine provides higher levels of antibodies. Also, the CDC recommends a 5-month interval for children 4-11 years because they are concerned about hyperimmune responses! But a new paper suggests immunity from COVID-19 Omicron infection peaks at 7 months and starts to wane only 16 months after infection. This protection was similar to prior reports, reducing likelihood of being infected by over 80%. 

Given this, people who were infected since about December of last year (when Omicron first arrived) have about 12 months after their infection before they require a booster. Consequently, there is no great rush to get a COVID booster, especially for those infected last spring.

Finally, many people have told me they are getting both the flu vaccine and their COVID booster at the same time because they want to get it over with and only have side effects once. While I understand this motivation there is a concern about this approach. 

With some vaccines we see a problem called “immune interference” where co-administering two vaccines reduces the immune response to one or both. You can think of this as the immune system being confused by having to address too many things at once. 

A recent editorial reviewed data that showed adverse reactions were slightly worse with the co-administration of COVID and flu vaccines and the immunity to COVID generated was less. Unfortunately, this data was from a study with the Novavax COVID vaccine, and therefore we don’t know if the same is true for the mRNA COVID vaccine boosters.

In any case, I think it’s wisest to get the flu vaccine right away, given there has been no flu immunity boost since last year’s vaccine. You should then wait at least two weeks or longer before getting the COVID vaccine booster based on your last booster or infection.