People who received the single-shot Johnson & Johnson COVID-19 vaccine are at higher risk of serious illness and hospitalization than those who received an mRNA vaccine, so they should seriously consider getting a booster dose of either Pfizer or Moderna’s shot, according to new Centers for Disease Control and Prevention (CDC) data released Tuesday.

Health officials first allowed people to mix and match booster shots last fall, but there’s been very little data on the real-world effectiveness of different strategies.

The CDC study of ten states during the height of the omicron wave found that people who received a single J&J dose combined with an mRNA booster shot had better protection against severe outcomes than those with just the J&J dose.

A single J&J dose provided only 31 percent protection against hospitalization. A booster dose of the J&J vaccine was better than a single dose, but people with three doses of mRNA vaccines had the best protection, with 90 percent effectiveness.