# Presentation: 287219

## Options  for 2001-2002 Influenza Vaccine Composition

- Summary of Data
- Options with Pros and Cons

## Influenza A(H1N1) Viruses

- Little antigenic heterogeneity observed
- HA of most strains antigenically similar to A/New Caledonia/99 vaccine strain
- The NA genes of current strains are similar to the vaccine strain
- Low reactors don’t fall into one genetic group
- H1N1 viruses are generally well inhibited by ferret and  human antiserum vs. A/New Caledonia
- Current vaccine strain in vaccine for 1 year

## H1N1 Option 1: Maintain Current Vaccine Strain

- Pros
- Current vaccine strain is immunogenic and well matched to currently circulating viruses
- Manufacturing is well-defined and predictable
- No new vaccine candidates are available
- Con
- A variant strain could be identified in the next 2-3 weeks

## H1N1 Option 2: Update Current Vaccine Strain

- Pro
- Might provide closer genetic match to next year’s viruses if correct sub lineage is chosen
- Cons
- No clear advantage based on antigenic characterization or serologic results
- No superior alternate vaccine candidate

## H1N1 Option 3. Defer to Accumulate Additional Data

- Pro
- More data will be available in the next 2-3 weeks (including analyses of new Chinese  H1N1 viruses)
- Con
- Additional data may not alter the current considerations since global data consistently indicate a good vaccine match

## Summary for Influenza A(H1N1) Viruses

- Although influenza activity associated with H1N1 viruses has been low worldwide in recent years, significant H1N1 activity has occurred this season.
- The majority of current viruses are antigenically similar to the A/New Caledonia/99 vaccine strain, however, viruses similar to the A/Johannesburg/96 reference strain were also identified.
- Human serologic responses suggest that the current vaccine strain is immunogenic and provides a good antibody response against current viruses from both antigenic/genetic groups.

## Influenza A(H3N2) Viruses

- Little antigenic heterogeneity observed
- HA of most strains antigenically similar to A/Panama/99 vaccine strain
- The NA genes of many current strains fall into a different genetic group from A/Panama/99
- Low reactors (few) do not fall into any particular genetic group
- H3N2 viruses are generally well inhibited by ferret and human antiserum vs. A/Panama/99
- Current vaccine strain in vaccine for 1 year

## H3N2 Option 1: Maintain Current Vaccine Strain

- Pros
- Current vaccine strain is immunogenic and well matched to currently circulating viruses
- Manufacturing is well-defined and predictable
- No obvious new vaccine candidate
- Con
- A new variant might be identified in the next 2-3 weeks

## H3N2 Option 2: Update Current Vaccine Strain

- Pro
- May provide closer genetic match to HA and especially to NA of next year’s viruses
- Cons
- No clear advantage based on antigenic characterization or serologic results
- No clear alternate vaccine candidate

## H3N2 Option 3: Defer to Accumulate Additional Data

- Pros
- Since H3N2 viruses cause most serious morbidity and mortality, choice should be made carefully
- A few additional pieces of data will be available in the next 2-3 weeks
- Con
- Additional data may be insufficient to alter current considerations

## Summary for Influenza A(H3N2) Viruses

- In contrast to most recent years, few H3N2 viruses have been isolated globally.
- Current viruses are antigenically similar to the A/Panama/99 vaccine strain.
- Serologic responses suggest that the current vaccine strain is immunogenic and provides an equivalent antibody response against most current viruses.

## Influenza B Viruses

- Antigenic drift has been detected
- A new variant represented by B/Sichuan/379/99 has been identified as a prototype variant strain
- The NA genes of many current strains are generally similar to vaccine strain
- No evidence for circulation of B/Vic-lineage strains
- B viruses are generally less well inhibited by ferret and human antiserum vs. B/Yamanashi/98
- Current vaccine strain in vaccine for 2 years

## Influenza B Option 1: Maintain Current Vaccine Strain

**Pros**
**Current vaccine strain is immunogenic **
**Manufacturing is well defined and predictable**
**Cons**
**Current influenza B strains are not well inhibited by ferret serum to vaccine strain**
**Human serologic responses vs. recent strains reduced**
**Egg isolates with appropriate antigenic properties are being evaluated as candidate vaccine strains**

## Influenza B Option 2: Update Current Vaccine Strain

**Pros**
**Provide a better antigenic match with current B strains**
**Vaccine candidate strains (e.g., B/JHB/5/99 and B/Vic/504/2000) were used to manufacture vaccines for the Southern Hemisphere**
**Cons**
**No data available on immunogenicity of vaccines produced with recent strains**
**Many recent influenza B egg isolates grow poorly**

## Influenza B Option 3: Defer to Accumulate Additional Data

- Pros
- More data will be available in the next 2-3 weeks, including analyses of new Chinese influenza B viruses
- More data are likely to be available on growth properties of potential vaccine candidates
- Cons
- Additional data may not alter current considerations

## Summary for Influenza B Viruses

- Antigenic drift from the vaccine strain, B/Yamanashi/98, is apparent among current influenza B viruses which are antigenically and genetically similar to the prototype reference strain, B/Sichuan/379/99.
- Serologic responses suggest that the current vaccine strain is immunogenic but may provide a more limited response against current B viruses.
- A great deal of work has been done to develop alternate vaccine candidates.