Recombinant Flu Vaccine FAQ: What You Need to Know

Instead of growing flu virus in eggs, RIV is made in a laboratory using insect cells. Scientists insert the gene for a key flu protein, called haemagglutinin (HA), into a carrier virus that infects insect cells, which then produce large quantities of that protein. This purified HA protein becomes the active ingredient in the vaccine.

Because no eggs are used at any stage, RIV contains absolutely no egg protein.

RIV contains three times the amount of HA protein per strain compared to a standard-dose inactivated influenza vaccine (45 micrograms per strain versus 15 micrograms). This higher dose is thought to be why it tends to produce a stronger immune response.

A large randomised trial found that adults aged 50 and over who received RIV had a 30% lower probability of developing influenza illness compared to those who received a standard-dose inactivated vaccine. For adults aged 65 and over, major international advisory bodies group RIV alongside other enhanced vaccines as the preferred choice over standard-dose inactivated vaccines.

• Adults and children aged 9 years and over
• Adults aged 65 and over (preferentially recommended by international guidelines)
• People with egg allergy, since the vaccine contains no egg protein and no special precautions are needed
• Pregnant women at any stage of pregnancy

RIV is not currently licensed for children under 9 years of age. Standard inactivated flu vaccines remain the appropriate choice for younger children from 6 months of age.

Yes. Both inactivated and recombinant flu vaccines are recommended during pregnancy, at any trimester. A large study of nearly 49,000 pregnant people found no meaningful difference in pregnancy, birth, or infant outcomes between those who received RIV and those who received a standard inactivated vaccine.

Vaccination in pregnancy also protects the baby for the first several months of life, as protective antibodies are passed through the placenta before the baby is old enough for their own flu vaccine. The only flu vaccine that must not be given in pregnancy is the live-attenuated intranasal influenza vaccine (LAIV), commonly known as the nasal spray flu vaccine.

Side effects are generally mild and short-lived. They may include:

• Pain, redness, or swelling at the injection site

• Headache

• Fatigue

• Muscle aches

• Fever or chills

Serious allergic reactions are rare. RIV should not be given to anyone with a known severe allergic reaction to any of its components.

RIV has very few clinically significant interactions with other medicines. Key points to be aware of include:

• Antiviral medicines (such as oseltamivir or zanamivir, used to treat or prevent flu): these do not reduce how well RIV works, and the vaccine can be given while taking them.

• Warfarin and theophylline: influenza vaccination can theoretically affect how the body processes these medicines, but clinical studies have not shown any harmful effects in practice.

• Anticonvulsant medicines (such as phenytoin or carbamazepine): case reports suggest drug levels may rise for up to four weeks after vaccination. Let your doctor know if you take these medicines so they can advise on any monitoring needed.

• Immunosuppressive medicines (such as those taken after organ transplant or for autoimmune conditions): these may reduce how well the vaccine works, though vaccination is still recommended.

People taking blood-thinning medicines or those with a bleeding disorder should speak to their doctor before receiving any injected vaccine.

Yes, in most cases. Receiving the flu jab at the same visit as other recommended vaccines is safe and is actively encouraged by international health organisations. Doing so reduces the number of separate appointments needed and helps ensure you are protected before the respiratory virus season begins.

The flu vaccine can be given at the same visit as:

• The COVID-19 vaccine, with no recommended waiting period between them

• The respiratory syncytial virus (RSV) vaccine, if you are eligible

• Vaccines given in pregnancy, including the whooping cough (Tdap) vaccine and the RSV vaccine

When more than one injection is given at the same visit, each one is administered at a different site, such as a different arm. You may notice slightly more redness or soreness at the injection sites when vaccines are given together compared with receiving them separately, but this is temporary and not a cause for concern.