HA titre measures the content in hemagglutinin. TCID50 measurees infectivity.

The two are completely different: You can havea preparation containing  inactivated virus with high HA titre . There is no correlation

There is difference between HA titres and TCID50 titres. if you have 10(8) HA titres per 1 ml of original virus does not mean you have 10(8) infectious virus titres per that ml. So, I prefer to do TCID50 titration. But you can covert TCID50 titres into plaque forming unit /ml by multiplying 0.7 x TCID50 titer (https://www.lgcstandards-atcc.org/Global/FAQs/4/8/Converting%20TCID50%20to%20plaque%20forming%20units%20PFU-124.aspx?geo_country=be)

HA titre measures the content in hemagglutinin. TCID50 measurees infectivity.

The two are completely different: You can havea preparation containing  inactivated virus with high HA titre . There is no correlation

It is a completely different measures. HA depend on the Haemagglutinin protein content in the virus. Even inactivated viruses have HA titre (Non-infectious viruses=No TCID50). TCID50 titration depend on the content of infectious virus in your stock.

So, if I have a good HA titer dose not mean I have good TCID50 titer, but the opposite is true.

HA titre and TCID50 are two completely different concepts. TCID50 would have to be performed for the new stock.

No, it is not possible to so.

there is no confirmed correlation between the antigenicity and the pathogenicity of  all influenza viruses.

I agree with the previous answers that the two assays measure different things, but if you want a very rough conversion factor to give you a ball park - in our hands, 1HAU approximates to 1E7 particles and 1E5 PFU or TCID50.  This is a very rough estimate though, and will be wildly sensitive to virus strain, cell type used for the infectivity assay, the parameters of the HA assay and ultimately, how well your virus stock has been grown up, transported and handled since.

Paul

Adding to Paul's comment, remember to aliquot the stock before you do the TCID assay so that the result applies to all the aliquots as freeze/thaw cycles will have an effect.

TCID50- completely depends on the infectious unit i.e. live virus

HA - Live as well as a simple physical particle (need not be live) will yield HA reaction.

I have published a very simple formula to calculate TCID50. The full paper can be downloaded from the following PubMed/Research gate links

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861875/

https://www.researchgate.net/publication/298789586_Determination_of_50_endpoint_titer_using_a_simple_formula?ev=prf_pub

How can I calculate the virus quantification by TCID50? - ResearchGate. Available from: https://www.researchgate.net/post/How_can_I_calculate_the_virus_quantification_by_TCID50#581348d0ed99e11ab021a501 [accessed Oct 28, 2016].

Article Determination of 50% endpoint titer using a simple formula

Provided that your virus was grown, harvested, and frozen properly (i.e. you did NOT destroy the virus infectivity during processing) you can make a reasonably good guess of TCID50/PFU titer based on the HA titer. For an influenza stock to have a titer of 1HA/50ul it must contain approximately 10^7 PARTICLES in those 50ul. The specific infectivity of influenza viruses varies under different conditions in different/labs, but 1/50 is a good estimate. So, 10^7 particles correspond to roughly 2x10^5 PFU. In other words, in a best case scenario a stock virus of 1HA/50ul would contain about 4x10^6 PFU/ml. A stock of 64HA/50ul would be about 2.56x10^8 PFU/ml, etc...

the number of particles based on HA titer will vary depending on the virus and on the growth media (eggs or cell culture):

https://www.researchgate.net/publication/292994913_Characterization_of_Human_Influenza_Viruses_Propagated_by_Madin-Darby_Canine_Kidney_Cells_or_Embryonated_Eggs

Article Characterization of Human Influenza Viruses Propagated by Ma...